Abstracts of project publications

(Molecular approaches to the diversity and history of boreal fauna)

Väinölä R, Strelkov P (2011) Mytilus trossulus in Northern Europe. Marine Biology 158: 817–833.

Abstract.   From data on allozyme, nuclear DNA and mitochondrial DNA markers, we show that the originally North Pacific/Northwest Atlantic mussel Mytilus trossulus is widespread on North European coasts, earlier thought to be inhabited only by Mytilus edulis. Several local occurrences of M. trossulus, interspersed with a dominant M. edulis, were recorded on the North Sea, Norwegian Sea and Barents Sea coasts of Norway and the Barents and White Sea coasts of Kola Peninsula in Russia. The proportion of M. trossulus genetic background observed at any one site varied from 0 to 95%. These new occurrences are not related to the previously known, introgressed M. trossulus population that occupies the Baltic Sea. The new northern occurrences retain both the F and M M. trossulus mitochondria, which have been lost from the Baltic stock. While hybridization takes place wherever M. trossulus and M. edulis meet, the extent of hybrization varies between the different contact areas. Hybrids are rare, and the hybrid zones are bimodal in the northern areas; more interbreeding has taken place further south in Norway, but even there genotypic disequilibria are higher than those in the steep transition zone between the Baltic mussel and M. edulis: there is no evidence of a collapse toward a hybrid swarm unlike in the Baltic. The Barents and White Sea M. trossulus are genetically slightly closer to the NW Atlantic than NE Pacific populations, while the Baltic mussel has unique features distinguishing it from the others. We postulate that the presence of M. trossulus in Northern Europe is a result of repeated independent inter- or transoceanic cryptic invasions of various ages, up to recent times [fulltext.pdf]

Audzijonyte A, Wittmann KJ, Ovcarenko I, Väinölä R (2009) Invasion phylogeography of the Ponto-Caspian crustacean Limnomysis benedeni dispersing across Europe. Diversity and Distributions 15: 346–355.

Abstract.   Limnomysis benedeni Czerniavsky, 1882 is a mysid crustacean native to the Ponto-Caspian rivers and estuaries of the Black and Caspian Seas, and has recently spread across Europe through intentional and unintentional introductions. We explored the structuring of genetic variation in native and non-native populations with an aim to trace the sources of the invasions, and to infer whether the spread has occurred through a single or multiple invasion waves. Material was collected from native estuaries in the Ponto-Caspian basin (Volga, Don, Dnieper, Dniester, Danube) and the recently colonized range along the Danube-Rhine river systems and Lithuania, and a fragment of the mitochondrial COI gene was sequenced to assess genetic affinities and diversity in native and recently established populations. The genetic diversity in the native regions was organized into several strongly diverged haplotype groups or lineages, partly allopatric, partly sympatric. All these lineages have also spread beyond the native range. Even the recent rapid dispersal across Europe along the Danube-Rhine system towards the North Sea basin involved several lineages from the Danube delta sector. The structuring of genetic diversity among invaded sites suggests multiple invasion events to the Danube-Rhine drainage. This contrasts with data from some other Ponto-Caspian species, where a single haplotype seems to have occupied most invaded areas. There is no evidence that intentionally stocked reservoirs in the Baltic Sea basin would have contributed to further unintentional spread of L. benedeni. We conclude that Limnomysis benedeni is spreading across Europe using the southern invasion corridor. The invasion most likely involved several waves from differentiated sources in the native Danube delta area.

Audzijonyte A, Ovcarenko I, Bastrop R, Väinölä R (2008) Two cryptic species of the Hediste diversicolor group (Polychaeta, Nereididae) in the Baltic Sea , with mitochondrial signatures of different colonization histories. Marine Biology 155:599–612.

Abstract.   A presence of two cryptic biological species of Hediste diversicolor complex polychaetes was corroborated in a geographical survey of some 30 populations from the eastern and southern coasts of the Baltic Sea, with data from four completely diagnostic allozyme characters. Species A was dominant in the northernmost part of the Baltic Hediste range (Bothnian Sea), whereas Species B alone was found in the south (Poland, Germany, Denmark). In the intervening region, comprising the majority of the sites studied in southern Finland and Estonia, the two species were usually found together, with no evidence of recent hybridisation (i.e., no heterozygote genotypes). While mitochondrial DNA also distinguished the two taxa, it was not similarly completely diagnostic, but there were rare cases (ca 5%) of lineage mismatch indicating that some introgression has occurred in the past. Comparison with published data suggests that species A also inhabits the North Sea–NE Atlantic–Mediterranean coasts, and species B is also present in the North Sea and the NW Atlantic (Canada). Within the Baltic, the two species show distinctly different patterns of mtDNA diversity, plausibly related to different colonisation histories. Species A shows a generally high haplotype and nucleotide diversity, whereas in species B we found only four deeply diverged groups of closely related haplotypes. Hypothetically this could indicate a recent expansion of species B from a small number of colonising individuals. Moreover, species B showed marked intraspecific geographical structuring, with co-incident genetic changes along the N Estonian–S Finnish coasts both in mtDNA and an allozyme marker; this pattern suggests a contact between two genetically distinct invasion waves of different origins. In all, species A and B represent good, reproductively isolated and partly sympatric species which require to be recognised in ecological work. A formal taxonomical description is needed, but awaits better, range-wide distributional and ecological characterisation and working out of morphological differences that enable a practical identification.

Nikula R, Strelkov P, Väinölä R (2008) A broad transition zone between an inner Baltic hybrid swarm and a pure North Sea subspecies of Macoma balthica (Mollusca, Bivalvia). Molecular Ecology 17: 1505-1522.

Abstract: The populations of the bivalve clam Macoma balthica in the low-salinity Northern Baltic Sea represent an admixture of two strongly diverged genomic origins, the Pacific Macoma balthica balthica (approx. 60 % genomic contribution) and Atlantic Macoma balthica rubra (40 %). Using allozyme and mtDNA characters, we describe the broad transition from this hybrid swarm to the pure M. b. rubra in the saline North Sea waters, spanning hundreds of km distance. The zone is centered in the strong salinity gradient of the narrow Öresund strait and in the adjacent Western Baltic. Yet the multilocus clines show no simple and smoothly monotonic gradation: they involve local reversals and strong differences between neighboring populations. The transitions in different characters are not strictly coincident, and the extent of introgression varies among loci. The Atlantic influence extends further into the Baltic in samples from the southern and eastern Baltic coasts than on the western coast, and further in deeper bottoms than at shallow (< 1 m) sites. This fits with the counterclockwise net circulation pattern, and with a presumably weaker salinity barrier for invading Atlantic type larvae in saline deeper water, and corresponding facilitation of outwards drift of Baltic larvae in diluted surface waters. Genotypic disequilibria were strong particularly in the shallow-water samples of the steepest transition zone. This suggests larval mixing from different sources and limited interbreeding in that area, which makes a stark contrast to the evidence of thorough amalgamation of the distinct genomic origins in the inner Baltic hybrid swarm of equilibrium structure.

Audzijonyte A, Daneliya, ME, Mugue N, Väinölä R (2008) Phylogeny of Paramysis (Crustacea: Mysida) and the origin of Ponto-Caspian endemic diversity: resolving power from nuclear protein coding genes. Molecular Phylogenetics and Evolution 46: 738-759.

Abstract: The Ponto-Caspian (Black and Caspian seas) brackish-water fauna represents a special case of the endemic diversification in world's ancient lakes; it also involves a hotspot of continental diversity in the predominantly marine mysid crustaceans. We explored the origins and history of the mysid diversification in a phylogenetic analysis of some 20 endemic Ponto-Caspian species mainly of the genus Paramysis and their marine congeners, using sequences of two nuclear protein-coding genes, two nuclear rRNA genes, the mitochondrial COI gene and morphological data. A nearly completely resolved phylogeny was recovered, with no indication of rapid diversification bursts. Deep divergences were found among the main endemic clades, attesting to a long independent faunal history in the continental Paratethys waters. The current marine Paramysis species make a monophyletic cluster secondarily derived from the continental Paratethyan (Ponto-Caspian) Paramysis ancestors. The good phylogenetic resolution was mainly due to the two nuclear protein-coding genes, opsin and EPRS, here for the first time applied to peracarid systematics. In contrast, ‘conventional' mtDNA and nuclear rRNA genes provided poor topological resolution and weak congruence of divergence rates. The two nuclear protein-coding genes had more congruent rates of evolution, and were about 10–15 times slower than the mitochondrial COI gene.

Audzijonyte A, Wittmann KJ, Väinölä R (2008) Tracing recent invasions of the Ponto-Caspian mysid shrimp Hemimysis anomala across Europe and to North America with mitochondrial DNA. Diversity and Distributions 14: 179-186.

Abstract: The mysid crustacean Hemimysis anomala (‘bloody-red shrimp') is one of the most recent participants in the invasion of European inland waters by Ponto-Caspian organisms. Recently the species also became established in England and in the Laurentian Great Lakes of North America. Using information from mitochondrial COI gene sequences we traced the invasion pathways of H. anomala ; the inferences were enabled by the observed phylogeographic subdivision among the source area populations in the estuaries of the Ponto-Caspian basin. The data distinguish two routes to northern and western Europe used by distinct lineages. One route has been to and through the Baltic Sea and further to the Rhine delta, probably from a population intentionally introduced to a Lithuanian water reservoir from the lower Dnieper River (NW Black Sea area) in 1960. The other lineage is derived from the Danube delta and has spread across the continent up the Danube River and further through the Main-Danube canal down to the Rhine River delta. Only the Danube lineage was found in England and in North America. The two lineages appear to have met secondarily and are now found intermixed at several sites in NW Europe, including the Rhine and waters linked with the man-made Mittellandkanal that now interconnects the Rhine and Baltic drainage systems.

Väinölä R, Witt JDS, Grabowski M, Bradbury JH, Jazdzewski K, Sket B (2008) Global diversity of amphipods (Amphipoda; Crustacea) in freshwater. In Balian E et al.(eds) Freshwater animal diversity assessment. Hydrobiologia 595: 241-255. (review article)

Abstract: Amphipods are brooding peracaridan crustaceans whose young undergo direct development, with no independent larval dispersal stage. Most species are epibenthic, benthic, or subterranean. There are some 1870 amphipod species and subspecies recognized from fresh or inland waters worldwide. This accounts for 20 % of the total known amphipod diversity. The actual diversity may still be several-fold. Amphipods are most abundant in cool and temperate environments; they are particularly diversified in subterranean environments and in running waters (fragmented habitats), and in temperate ancient lakes, but are notably rare in the tropics. Of the described freshwater taxa 70 % are Palearctic, 13 % Nearctic, 7 % Neotropical, 6 % Australasian and 3 % Afrotropical. Approximately 45 % of the taxa are subterranean; subterranean diversity is highest in the karst landscapes of Central and Southern Europe (e.g. Niphargidae), North America (Crangonyctidae), and Australia (Paramelitidae). The majority of Palearctic epigean amphipods are in the superfamily Gammaroidea, whereas talitroid amphipods ( Hyalella ) account for all Neotropic and much of the Nearctic epigean fauna. Major concentrations of endemic species diversity occur in Southern Europe, Lake Baikal , the Ponto-Caspian basin, Southern Australia (including Tasmania ) and the south-eastern USA . Endemic family diversity is similarly centered in the Western Palearctic and Lake Baikal . Freshwater amphipods are greatly polyphyletic, continental invasions have taken place repeatedly in different time frames and regions of the world. In the recent decades, human mediated invasions of Ponto-Caspian amphipods have had great impacts on European fluvial ecosystems.

Daneliya ME, Audzijonyte A, Väinölä R (2007) Diversity within the Ponto-Caspian Paramysis baeri Czerniavsky sensu lato revisited: P. bakuensis G.O. Sars restored (Crustacea: Mysida: Mysidae). Zootaxa 1632: 21-36.

Abstract: The Ponto-Caspian mysid crustacean Paramysis bakuensis G.O. Sars, 1895, which was previously synonymized with P. baeri Czerniavsky, 1882, is restored on the basis of new morphological and molecular characters. The Sea of Azov subspecies P. baeri bispinosa Martynov, 1924, in turn, is synonymised with P. bakuensis . The two species, P. baeri and P. bakuensis , are distinguished by the shapes of paradactylar setae of pereiopods, maxilla II exopod and antennal scale, and by the number of denticles in the telson cleft. They also are characterized by ca 7% divergence in mitochondrial COI gene sequences. P. bakuensis is shown to be a widespread species, distributed in estuaries and rivers of the Caspian, Azov and Black Sea basins and in the Caspian Sea itself. P. baeri is endemic to the Caspian Sea , where the two species overlap and are sometimes found together.

Strelkov P, Nikula R, Väinölä R (2007) Macoma balthica in the White and Barents Seas: properties of a widespread marine hybrid swarm. Molecular Ecology 16: 4110-4127.

Abstract: A main molecular subdivision in the circumpolar Macoma balthica complex has been described between Atlantic and Pacific taxa. In NE Europe the clams of the White and Barents Seas however show deviant genetic structures. Using allozyme and mtDNA data we explore the hypothesis that these deviations result from hybridisation between an Atlantic ( M. b. rubra ) and an invading Pacific ( M. b. balthica ) lineage. A practically pure Atlantic Macoma extends from France north to the Varanger Peninsula (NE Norway), whereas populations further east have genetic compositions intermediate between true Atlantic and true Pacific. Admixture estimates range from 32% to 90% Pacific contribution, with a notable deviation in a nearly pure Atlantic outpost in the Mezen Bay (NE White Sea). The pattern of variation is not one of a simple collinear mixing however. Different characters exhibit different degrees of introgression, and the relative introgression varies regionally. Yet there are practically no inter-locus genotypic disequilibria between the diverged loci, which brings out the White Sea – Barents Sea M. balthica as the best documented marine animal hybrid swarms so far, arisen through amalgamation of genomes previously isolated since pre-Pleistocene times. On top of the main admixture pattern, strong geographical structuring is also seen in characters unrelated to the principal systematic distinction. The persistence of the regional patterns indicates restricted gene flow at present time, despite the high dispersal potential of the species. The causes of this structuring could be in a complex history of colonisation events and features of local hydrography enhancing isolation and divergence of populations.

Audzijonyte A, Väinölä R (2007) Mysis nordenskioldi n.sp. (Crustacea, Mysida), a circumpolar coastal mysid separated from the NE Pacific M. litoralis (Banner, 1948). Polar Biology 30:1137-1157.

Abstract: Mysis nordenskioldi n. sp. is a circumpolar, arctic-subarctic coastal mysid crustacean, earlier considered conspecific with M. litoralis (Banner, 1948) and in the past also confused with the circumpolar M. oculata (Fabricius, 1780). M. litoralis itself seems to be restricted to the northeastern North Pacific. Formal diagnoses and descriptions of the three species are here given based on morphological and molecular characters (allozymes, mtDNA). The species are morphologically distinguished by features of the telson and by the setation of maxillae and maxillipedes. Molecular differences diagnosing M. nordenskioldi from the two others were found at 8 allozyme loci, while M. oculata and M. litoralis differed from each other at 4-5 loci. In mitochondrial DNA, M. nordenskioldi is distinguished from the others by 8% nucleotide divergence, whereas M. litoralis and M. oculata make an inseparable cluster (< 1%), suggesting post-speciation mitochondrial introgression. Initial phylogeographic data on M. nordenskioldi and M. oculata are presented. A morphological key to marine Mysis species is given.

Nikula R, Strelkov P, Väinölä R (2007) Diversity and trans-Arctic invasion history of mitochondrial lineages in the North Atlantic Macoma balthica complex (Bivalvia: Tellinidae). Evolution 61: 928-941.

Abstract: The history of repeated inter- or trans-oceanic invasions in bivalve mollusks of the circumpolar Macoma balthica complex was assessed from mtDNA COIII sequences. The data suggest that four independent trans-Arctic invasions, from the Pacific, gave rise to the current lineage diversity in the North Atlantic. Unlike in many other prominent North Atlantic littoral taxa, no evidence for (post-invasion) trans-Atlantic connections was found in the M. balthica complex. The earliest branch of the mtDNA tree is represented by the temperate-boreal North American populations (= Macoma petalum ) , separated from the M. balthica complex proper in the Early Pliocene at latest. The ensuing trans-Arctic invasions established the North European M. b. rubra, which now prevails on the North Sea and NE Atlantic coasts, about 2 Mya, and the currently NW Atlantic M. balthica lineage in the Canadian Maritimes, in the Middle Pleistocene. The final re-invasion(s) introduced a lineage that now prevails in a number of North European marginal seas and is still hardly distinguishable from North Pacific mtDNA ( M. b. balthica ). We used coalescence simulation analyses to assess the age of the latest invasion from the Pacific to the NE Atlantic . The results refute the hypothesis of recent, human-mediated reintroductions between NE Pacific and the North European marginal seas in historical times. Yet they also poorly fit the alternative hypotheses of an early post-glacial trans-Arctic invasion (< 11 kya), or an invasion during the previous Eemian interglacial (120 kya). Divergence time estimates rather fall in the Middle Weichselian before the Last Glacial Maximum, in conflict with the conventional thinking of trans-Arctic biogeographical connections; an early Holocene reinvasion may still be regarded as the most plausible scenario. Today, the most recently invaded Pacific mtDNA lineage is found admixed with the earlier established European Atlantic 'rubra' lineage in the Baltic Sea and in Barents Sea populations east of the Varanger peninsula, and it is practically exclusive in the White and Pechora seas. Yet mtDNA does not constitute an unequivocal taxonomic marker at individual level; the marginal populations represent hybrid swarms of the Atlantic and Pacific lineages in their nuclear genes.

Audzijonyte A, Daneliya ME, Väinölä R (2006) Comparative phylogeography of Ponto-Caspian mysid crustaceans: isolation and exchange among dynamic inland sea basins. Molecular Ecology 15: 2969-2984.

Abstract:  The distributions of many endemic Ponto-Caspian brackish-water taxa are subdivided among the Black, Azov and Caspian Sea basins and further among river estuaries. Of the two alternative views to explain the distributions, the relict school has claimed Tertiary fragmentation of the once contiguous range by emerging geographical and salinity barriers, whereas the immigration view has suggested recolonisation of the westerly populations from the Caspian Sea after extirpation during Late Pleistocene environmental perturbations. A study of mitochondrial (COI) phylogeography of seven mysid crustacean taxa from the genera Limnomysis and Paramysis showed that both scenarios can be valid for different species. Four taxa had distinct lineages related to the major basin subdivision, but the lineage distributions and depths of divergence were not concordant. The data do not support a hypothesis of Late Miocene (10-5 Myr) vicariance; rather, range subdivisions and dispersal from and to the Caspian Sea seem to have occurred at different times throughout the Pleistocene. For example, in P . lacustris each basin had an endemic clade 2-5% diverged from the others, whereas P . kessleri from the southern Caspian and the western Black Sea were nearly identical. Species-specific ecological characteristics such as vagility and salinity tolerance seem to have played important roles in shaping the phylogeographic patterns. The mitochondrial data also suggested recent, human-mediated cryptic invasions of P. lacustris and L. benedeni from the Caspian to the Sea of Azov basin via the Volga-Don canal. Cryptic species-level subdivisions were recorded in populations attributed to P. baeri, and possibly in P. lacustris..

Audzijonyte A, Väinölä R (2006) Phylogeographic analyses of a circumarctic coastal and a boreal lacustrine mysid crustacean, and evidence of fast post-glacial mtDNA rates. Molecular Ecology 15: 3287-3301.

Abstract: Phylogeographic structures of two weakly dispersing Mysis sibling species, one with a circumarctic coastal, the other with a boreal lacustrine-Baltic distribution, were studied from mitochondrial COI gene sequences. Mysis segerstralei showed high overall diversity and little phylogeographic structure across the Arctic, indicating late-glacial dispersal among coastal and lake populations from Alaska, Siberia and the north of Europe. A strongly divergent refugial lineage was however identified in Beringia. The boreal ‘glacial relict' Mysis salemaai in turn displayed clear structuring among post-glacially isolated Scandinavian lake populations. The inferred pattern of intra-lake mtDNA monophyly in Scandinavia suggested relatively small population sizes and a remarkably fast post-glacial mtDNA divergence rate (0.27% per 10 kyr). The broader phylogeographic pattern nevertheless did not support distinct eastern and western glacial refugia in Northern Europe, unlike in some other aquatic taxa. In all, the two species comprised three equidistant mitochondrial lineages (ca 2% divergence), corresponding to M. salemaai, to the bulk of M. segerstralei, and to the Beringian M. segerstralei lineage. The lack of reciprocal monophyly of the two species in respect to their mitochondrial genealogy could indicate post-speciation mitochondrial introgression, also exemplified by an evidently more recent capture of M. segerstralei mitochondria in a Karelian population of M. salemaai. Overall, the data suggest that the continental boreal M. salemaai has a relatively recent ancestry in arctic coastal waters, whereas two other boreal ‘glacial relict' Mysis sibling species in Europe (M. relicta) and North America (M. diluviana) have colonised inland waters much earlier (ca 8 % COI divergence).

Palo JU, Väinölä R (2006) The enigma of the landlocked Baikal and Caspian seals addressed through phylogeny of phocine mitochondrial sequences. Biological Journal of the Linnean Society 88: 61-72.

Abstract:  The endemic seals of Lake Baikal ( Phoca sibirica ) and of the Caspian Sea ( P. caspica ) inhabit ancient continental basins that have remained isolated from primary marine seal habitats for millions of years. The species have been united with the Arctic ringed seal P. hispida into (sub)genus Pusa , but the age and route of invasions to/from the continental basins remain controversial. A phylogenetic analysis of nine northern phocines based on three mitochondrial genes (Cyt b , COI, COII, total 3369 bp) provided no support for the monophyly of the Pusa group. The three species are involved in an apparent polytomy with the boreal harbour seal Phoca vitulina and grey seal Halichoerus grypus. From the average estimated interspecies divergence (4.1%), the radiation of this group plausibly took place in the Late Pliocene 2-3 Myr ago. This dating does not fit the prevailing hypotheses on the origin of the landlocked taxa in association with Middle Pleistocene glacial events, or of the Caspian seal as a direct descendant of Miocene fossil phocines of the continental Paratethyan basin. The current phocine diversity more likely results from marine radiations, and the continental seals invaded their basins through Plio-Pleistocene (marine) connections from the north. The paleohydrography that would have enabled the invasions at that time still remains an enigma.

Audzijonyte A, Damgaard J, Varvio SL, Vainio JK, Väinölä R (2005) Phylogeny of Mysis (Crustacea, Mysida): history of continental invasions inferred from molecular and morphological data. Cladistics 21: 575-596.

Abstract:  We studied the phylogenetic history of opossum shrimps of the genus Mysis Latreille, 1802 (Crustacea: Mysida) using parsimony analyses of morphological characters, of DNA sequence data from mitochondrial (16S, COI and CytB) and nuclear genes (ITS2, 18S), and of eight allozyme loci. With these data we aimed to resolve a long-debated question of the origin of the non-marine (continental) taxa in the genus, i.e., "glacial relicts" in circumpolar postglacial lakes and "arctic immigrants" in the Caspian Sea. A simultaneous analysis of the data sets gave a single tree supporting monophyly of all continental species, as well as monophyly of the taxa from circumpolar lakes and from the Caspian Sea. A clade of three circumarctic marine species was sister group to the continental taxa, whereas Atlantic species had more distant relationships to the others. Small molecular differentiation among the morphologically diverse endemic species from the Caspian Sea suggested their recent speciation, while the phenotypically more uniform "glacial relict" species from circumpolar lakes (Mysis relicta group) showed deep molecular divergences. For the length-variable ITS2 region both direct optimization and a priori alignment procedures gave similar topologies, although the former approach provided a better overall resolution. In terms of partitioned Bremer support (PBS), mitochondrial protein coding genes provided the largest contribution (83%) to the total tree resolution. This estimate however, appears to be partly spurious, due to the concerted inheritance of mitochondrial characters and probable cases of introgression or ancestral polymorphism.

Audzijonyte A, Väinölä R (2005) Diversity and distributions of circumpolar fresh- and brackish-water Mysis (Crustacea: Mysida): descriptions of M. relicta Lovén, 1862, M. salemaai n.sp., M. segerstralei n.sp. and M. diluviana n.sp., based on molecular and morphological characters. Hydrobiologia 544: 89-141.

Abstract:  Mysid crustaceans of the Mysis relicta species group are widespread throughout the northern Holarctic and play an important role in many fresh- and brackish-water ecosystems. Earlier molecular and morphometric studies already indicated that the conventionally identified Mysis relicta sensu lato comprises several distinct species. Here we present formal taxonomic diagnoses, descriptions and an account of the distributions of Mysis relicta s. str. and three new species split from it, based on comprehensive assessment of both morphological and molecular characters (allozymes, mtDNA). M. relicta Lovén s. str. is the prevalent species in lakes of Northern Europe and peripheral parts of the brackish Baltic Sea. M. salemaai n. sp. inhabits offshore habitats of the Baltic Sea and a range of lakes from the British Isles, southern Scandinavia and Karelia to coastal northern Siberia; at several sites M. relicta and M. salemaai are sympatric. M. segerstralei n. sp. has a circumpolar distribution along the Arctic coasts and islands of Eurasia and North America and also occurs in lakes of these northern regions. M. diluviana n. sp. inhabits continental freshwater lakes of the once-glaciated northern North America. The four species are characterised by unique combinations of alleles at a number of allozyme loci, and most of them by specific mitochondrial DNA lineages diverged by c. 7.5% in the COI gene sequence (cytochrome oxidase subunit I). The most important diagnostic morphological characters include the shape of the posterior emargination of carapace, length of setae on the merus of maxillipede 2, length and shape of spine-setae on maxilla endopod distal segment, number and size of lateral spine-setae on telson, and setation of thoracic endopods. A morphological key to the four species is presented.

Audzijonyte A , Pahlberg J, Väinölä R, Lindström M (2005) Spectral sensitivity differences in two Mysis sibling species (Crustacea, Mysida): Adaptation or phylogenetic constraints? Journal of Experimental Marine Biology and Ecology 325: 228-239.

Abstract:  The variation in eye spectral sensitivities of the closely related mysid species Mysis relicta Lovén, 1862 and Mysis salemaai Audzijonyte and Väinölä, 2005 was studied in sympatric and allopatric populations from the brackish Baltic Sea and from two lakes representing different light environments. In the Baltic Sea the maximum spectral sensitivity of M. relicta, measured by the electroretinogram (ERG) technique, was shifted by ca 20 nm to longer wavelengths than in M. salemaai (564 and 545 nm, respectively). The spectral sensitivity of M. salemaai was closer to that of marine mysid species, which is consistent with its broader euryhalinity and the presumed longer brackish-water history. The species-specific sensitivities in the Baltic Sea were not affected by regional differences in light environments. In two lake populations of M. relicta , the spectral sensitivity was further shifted by ca 28 nm towards the longer wavelengths compared with the conspecific Baltic Sea populations. The spectral sensitivities in the four M. relicta populations were not correlated to the current light conditions, but rather to the phylogeographic histories and fresh- vs. brackish-water environments. A framework to further explore factors affecting spectral sensitivities in Mysis is suggested.

Kontula T, Vainola R (2004) Molecular and morphological analysis of secondary contact zones of Cottus gobio in Fennoscandia: geographical discordance of character transitions. Biological  Journal of the Linnean Society 81: 531-552.

Abstract: Northern Europe was postglacially colonized from different directions by distinct phylogeographical lineages of the bullhead Cottus gobio L. (Pisces: Scorpaeniformes). These lineages have then come into contact in coastal habitats of the currently brackish Baltic Sea and in the freshwaters north of it. We studied the patterns of intergradation in the contact zones in four morphometric and six molecular characters. In the north, intergradation between the western (W) and eastern (E) bullhead lineages is found both among rivers (west-to-east) and along individual rivers (south-to-north). The locations of the transition zones probably relate to the timing of the initial contact, subsequent Baltic shoreline displacement (i.e. emergence of the lower river reaches), and dispersal barriers caused by variations of coastal salinity. The transitions (clines) in different characters are, however, not geographically coincident. Mitochondrial DNA clines are generally found upstream and to the east of the other transitions, and GPI-1 allozyme clines are mostly shifted downstream in the rivers, and west of the other transitions on the broader scale of the Baltic Sea. The location of the mtDNA clines may best reflect the initial contact between lineages, and the displacement of the other clines could result from dispersal being overall asymmetric (predominantly downstream) and sex-biased (stronger in males). Alternatively, the non-coincidence might reflect selection against deleterious cytonuclear character combinations. No clear evidence of reproductive incompatibility between the lineages was seen in local population structures; no remaining genetic correlations were observed locally among traits. In another transition area, a coastal transect in southern Finland, clinal patterns similar to those in the northern contact zone were recorded, but the population compositions could not be explained by simple in situ mixing of any of the putatively pure, invading refugial lineages. Probably, the bullhead stocks that initially came into contact in this southern study area already represented mixtures of the invading lineages.

Vainola Risto (2003) Repeated trans-Arctic invasions in littoral bivalves: molecular zoogeography of the Macoma balthica complex. Marine Biology 143: 935-946.

Abstract: From a geographical survey of allozyme variation, a history of repeated trans-Arctic invasions since the Plio-Pleistocene is suggested for circumboreal bivalves of the Macoma balthica complex. A principal genetic subdivision, involving several nearly diagnostic loci and Nei's distance D=0.6, distinguishes the clams of the NE Pacific from those of the NE Atlantic. The Pacific taxon is however also present in Europe, in disjunct isolates in the Baltic Sea and White Sea basins. Nevertheless, these populations have marked Atlantic introgressive elements in their gene pools (ca. 30%). Two further population types are recognized, one in the St. Lawrence estuary, Quebec, the other in Varangerfjorden, NE Norway; the latter appears a mixture of Pacific and Atlantic components in almost equal proportions, in local genetic equilibrium (a hybrid swarm). Populations in temperate North America fall outside the circumboreal M. balthica complex discussed here (D=1.0), and are referred to M. petalum. In a scenario of the history and evolution of the M. balthica complex and the similarly subdivided Mytilus edulis complex, the divergence between Pacific and Atlantic taxa started after an initial introduction of Pacific ancestors to the Atlantic basin, enabled by the Pliocene opening of the Bering Strait. During the Pleistocene and Holocene, the ocean basins were, for the most part, effectively isolated, but occasional re-invasions have taken place, causing secondary contacts of the diverged bivalve types on the Atlantic coasts. The recently re-invaded Pacific taxa in northern Europe now seem to thrive only in the extreme marginal environments. Exact dating of the re-invasions is not possible from current data. Apart from the divergence through isolation, hybridization and introgression have significantly molded the present affinities within the M. balthica complex. A formal taxonomic treatment of reticulate and hybridizing lineages is problematic; yet to recognize the evolutionary and systematic diversity within the M. balthica complex, a subspecies distinction between the NE Atlantic clams and those from the Pacific, Baltic and White Sea basins is suggested.

Nikula R, Vainola R (2003) Phylogeography of Cerastoderma glaucum (Bivalvia: Cardiidae) across Europe: A major break in the Eastern Mediterranean. Marine Biology 143: 339-350.

Abstract: Molecular variation of the lagoon cockle Cerastoderma glaucum (Poiret, 1789) was examined across the species range along European coasts, from the northern Baltic to the Black Sea and the Caspian Sea. A major phylogeographic break in mitochondrial COI gene sequences (divergence 6.2%) separated a group of Ponto-Caspian and Aegean Sea haplotypes from those to the west of the Peloponnese peninsula in the Mediterranean and in the Atlantic-Baltic sector. A similar subdivision, yet not entirely geographically coincident, was found at 16 allozyme loci (Nei's distance D = 0.15). The results imply a long-term isolation of populations in parts of the Eastern Mediterranean or Black Sea basins through the Pleistocene. The subdivision does not concur with previous views on the systematics of C. glaucum complex, but the pattern is notably similar to that described earlier from some fish species. Marked phylogeographic structuring was also found at lower level within the major Mediterranean-Atlantic phylogroup of C. glaucum, which was divided into six regional or local haplotype subgroups. Divergence of these groups may date back one or several major Pleistocene climatic cycles. Local mtDNA diversity was particularly high in a sample from the Ionian Sea, whose mitochondrial identity was of the Mediterranean-Atlantic type, while its nuclear characters were more strongly associated with the Ponto-Caspian type. Patterns of shallower, star-phylogeny type diversity within the Ponto-Caspian phylogroup and in the Baltic Sea area may represent more recent, post-glacial generation of variation.

Kontula T, Vainola R (2003) Relationships of Palearctic and Nearctic 'glacial relict' Myoxocephalus sculpins from mitochondrial DNA data. Molecular Ecology 12: 3179-3184.

Abstract: The relationships among Myoxocephalus quadricornis complex fish from Arctic coastal waters and from 'glacial relict' populations in Nearctic and Palearctic postglacial lakes were assessed using mtDNA sequence data (1978 bp). A principal phylogeographical split separated the North American continental deepwater sculpin (M. q. thompsonii) from a lineage of the Arctic marine and North European landlocked populations of the fourhorn sculpin (M. q. quadricornis). The North American continental invasion took place several glaciation cycles ago in the Early-to-Middle Pleistocene (0.9% sequence divergence); the divergence of the European and Arctic populations was somewhat later (0.5% divergence). The Nearctic-Palearctic freshwater vicariance in Myoxocephalus, however, appears clearly younger than in similarly distributed 'glacial relict' crustacean taxa; the phylogeographical structure is more similar to that in other northern Holarctic freshwater fish complexes.

Vainio JK, Vainola R (2003) Refugial races and postglacial colonization history of the freshwater amphipod Gammarus lacustris in Northern Europe. Biological  Journal of the Linnean Society 79: 523-542.  

Abstract: The systematic structure and postglacial population history of the freshwater amphipod Gammarus lacustris were explored in an allozyme survey of 65 populations across Northern Europe. A strong multilocus pattern of differentiation discriminated populations of the north-east (north-eastern Norway, northern Finland) from those in the west and the south (southern and central Scandinavia, Denmark, Poland). This principal division is attributed to postglacial colonization of the area by two main refugial races or lineages, one from the east (Russia), the other from the south (north-western European continent). The strongly diverged Eastern and Western races (Nei's D = 0.3, from 22 loci) now meet in a secondary contact zone across a narrow sector of northernmost Norway. Genetic population compositions in this zone vary in a mosaic pattern, and show no evidence of reproductive incompatibility. Similar contacts of eastern and western lineages, far older than the latest glaciation, are now known from a number of taxa and they constitute a general pattern in Fennoscandian phylogeography. – Within the Western Gammarus race, the populations through coastal north-western Norway are further distinguished from those in southern Scandinavia and Denmark by a set of unique alleles at high frequencies (D = 0.12). This suggests an independent early colonization of the coastal region by another distinct stock, either along an early-deglaciated coastal corridor from the south-west, or directly from the ice-free continental shelf off the Norwegian coast - a hypothesis that has also previously been presented for G. lacustris, and parallels controversial suggestions of local refugia for other taxa in Scandinavia. The coastal population type only later could come into contact with Gammarus invading over the mountains from the south; these two population types now smoothly intergrade.

Kontula T, Kirilchik SV, Vainola R (2003): Endemic diversification of the monophyletic cottoid fish species flock in Lake Baikal explored with mtDNA sequencing. Molecular Phylogenetics and Evolution 27: 143-155.

Abstract: In the ancient Lake Baikal in East Siberia, cottoid fishes have diversified into an endemic flock of 33 species. From an ancestral shallow-water, benthic life-style, Baikalian cottoids have shifted to deep-water life in environments even below 1500 m, and also colonized the pelagic habitat. We examined phylogenetic relationships among 22 Baikalian and 10 extra-Baikalian cottoid taxa using a total of 2822 bp of mitochondrial DNA sequence, from complete sequences of ATPase 8 and 6 and cytochrome b genes and the control region. Unlike in earlier studies, we found strong support for a monophyly of the whole endemic Baikalian cottoid diversity. The Baikalian clade, currently assigned to three families and 12 genera, appears to be nested within the Holarctic freshwater genus Cottus. In the molecular phylogeny, all but one of the current Baikalian genera formed well-supported monophyletic groups. However, the topology was inconsistent with the present morphology-based familial subdivision; particularly in positioning the genus Batrachocottus of Cottidae within Abyssocottidae. The branching order of the Baikalian genera could not be resolved completely, however; short basal branches indicate rapid diversification early in the history of the species flock. Using synonymous divergence rates from other fish species for calibration, the diversification of the Baikalian cottoids seems to have started in the Pliocene or early Pleistocene.

Palo JU, Hyvärinen H, Helle E, Mäkinen HS, Väinölä R (2003) Postglacial loss of microsatellite variation in the landlocked Lake Saimaa ringed seal. Conservation Genetics 4: 117-128.

Abstract: The Lake Saimaa ringed seal Phoca hispida saimensis has lived as an isolated landlocked population in eastern Finland since the early post-glacial. In the last century, the population crashed down to c. 200 individuals, and is under a constant threat of extinction. We evaluated the genetic history of the Saimaa population through a comparison with the conspecific sister populations in the Arctic Ocean and the Baltic Sea, which have retained high levels of variation since the deglaciation. At eight microsatellite loci, the current gene diversity (heterozygosity) of the Saimaa seal was 69% lower than in the reference populations. Allowing reasonable mutation rates (mu = 10(-4)), this implies a long- term post-glacial effective population size of N-e ~ 350, and a slow average rate of inbreeding DeltaF ~ 0.15% per generation during the c. 860 generations (9 500 years) of isolation. The current N-e is an order of magnitude smaller and DeltaF correspondingly larger. Whereas the additional loss of marker variation in the short term will not be high relative to that already taken place, it seems unwarranted to suppose that the past, slow inbreeding would have effectively purged the population of genetic load and reduced the genetic risks from small population size. Although the population is now clearly geographically subdivided in the complex lake system, we found little genetic differentiation between main breeding areas ( F-ST = 0.02). However, at the current low population densities, the subdivision may markedly further increase the future rate of inbreeding.

Vainola R, Audzijonyte A, Riddoch BJ (2002) Morphometric discrimination among four species of the Mysis relicta group. Archiv für Hydrobiologie 155: 493-515.

Abstract: Mysid crustaceans of the Mysis relicta group play central roles in many fresh- and brackish-water ecosystems both in northern Eurasia and North America. Yet, the recent division of the taxon into four sibling species by molecular criteria has largely remained unnoticed in ecological studies. We illustrate the morphometric differences among these species and the feasibility of their practical discrimination using multivariate analyses of 31 metric and meristic traits. The main patterns of size-independent variation identified in principal component analysis of individuals and in canonical variate analysis of populations corresponded to their assignment to the allozymically delineated species. The main variables contributing to discrimination described the spines or setae of the telson, uropods and maxillae, and the shape of the telson cleft. The subarctic sp. III was the phenetically most distinct from the others. The European stenohaline sp. I appeared intermediate between the North American freshwater sp. IV and the European euryhaline sp. II. In discriminant analyses between individual species pairs, 97-100% correct identification was obtained using 3-10 characters. The discriminant function for sp. I vs. sp. II, whose distributions overlap in northern Europe, was tested with independent material, and found to be a reliable means of species identification both at population level and at individual level in sympatric populations.

Kontula T, Vainola R (2001) Postglacial colonization of Northern Europe by distinct phylogeographic lineages of the bullhead, Cottus gobio. Molecular Ecology 10: 1983-2002.

Abstract: Three major phylogeographic lineages of the cottid fish Cottus gobio (bullhead) were identified in northern Europe from mitochondrial DNA sequences and allozyme data. The largely separate freshwater distributions of the lineages demonstrate distinct postglacial colonization histories. West of the Baltic Sea, Swedish lakes were invaded from the southwest (Germany). Another, eastern lineage has colonized the inland waters northeast and east of the Baltic, from refugia in northwest Russia; this lineage comprises a distinct subgroup found only from Estonia. The third lineage, found south and southeast of the Baltic, probably descended from rivers draining to the Black Sea from the north (e.g. Dnepr). In coastal waters of the Baltic Sea, and in near-coast inland waters, the lineages are now found intermixed in various combinations. The alternating fresh- and saltwater phases of the Baltic basin have variously enabled and disabled the use of coastal waters as colonization routes. Hypotheses on the chronology of dispersal and lineage mixing can be based on the distribution of the marker genes and the palaeohydrographical record. The diversity of the Fennoscandian bullhead thus comprises anciently diverged (probably mid-Pleistocene) refugial lineages that in their freshwater range constitute distinct evolutionarily significant units. The thorough mixing of the various genomic origins in and around the Baltic, however, refutes the controversial view of distinct species status for the western and eastern ('Cottus koshewnikowi') bullheads. The postglacial contact of the lineages has created new diversity that cannot be interpreted in a conventional hierarchical framework of taxonomic or conservation units

Vainola R, Oulasvirta P (2001) The first record of Maeotias marginata (Cnidaria, Hydrozoa) from the Baltic Sea: a Pontocaspian invader. Sarsia 86: 401-404.

Abstract: An exotic hydromedusa, Maeotias marginata (Modeer, 1791) (= M. inexpectata Ostroumoff, 1896) (Limnomedusae, Olindiidae) was observed 1999 in the Vainameri area of the northern Baltic Sea, western Estonia. The genuine brackishwater species is considered native to the Sea of Azov - Black Sea estuaries. It has earlier been found introduced also in low-salinity habitats in the Netherlands, France, and both coasts of North America. The identity of the Baltic and North American Maeotias was confirmed using molecular characters (sequence of the mitochondrial COI gene).

Vainola R, Vainio JK, Palo JU (2001) Phylogeography of "glacial relict" Gammaracanthus (Crustacea, Amphipoda) from boreal lakes and the Caspian and White Seas. Canadian Journal of Fisheries and Aquatic Sciences 58: 2247-2257.

Abstract: As with a number of "glacial relict" crustacean genera, species of Gammaracanthus are vicariously distributed in circumarctic coastal waters, in boreal freshwater lakes, and in the Caspian Sea. Various hypotheses have been invoked to explain the origins and diversity of the non-marine taxa. Data on 28 allozyme loci and 558 bp of the mitochondrial COI gene demonstrate a close affinity between G. caspius of the Caspian Sea and G. aestuariorum of the White Sea area (Nei's allozyme distance D = 0.09, COI sequence divergence d = 5%), and a threefold divergence of the two from the Fennoscandian freshwater G. lacustris (D = 0.33, d = 12%). The relative molecular affinities agree with morphological evidence but contradict the idea of a common ancestry of the non-marine taxa, rather they suggest two independent invasions of continental waters. The generally low molecular divergence refutes the recently suggested generic splitting of Gammaracanthus. Previous speculations of an affinity of Gammaracanthus to the Baikalian acanthogammarids or to the Eusiroidea are not substantiated. The interspecific phylogeographic structure of Gammaracanthus is not concordant with that of other "glacial relict" crustacean genera. Phylogeographically, Gammaracanthus seems to match with the genus Monoporeia alone, rather than with Pontoporeia sensu lato.

Palo JU, Makinen HS, Helle E, Stenman O, Vainola R (2001) Microsatellite variation in ringed seals (Phoca hispida): genetic structure and history of the Baltic Sea population. Heredity 86: 609-617.

Abstract: Genetic variability and population structure of Baltic ringed seals and an Arctic reference population were assessed using eight microsatellite loci. Ringed seals colonized the Baltic Sea basin soon after deglaciation 11 500 years ago and are supposed to have remained largely isolated from the main Arctic stock since then, approximate to 1000 generations. In the 1900s the Baltic population declined rapidly, and is now confined to three distinct breeding areas, with N < 6000 seals altogether. Microsatellite heterozygosity in ringed seals was higher than that in the closely related, boreal harbour seal and grey seal, for which the markers were initially developed. This is plausibly attributed to an overall greater population (species) size of ringed seals during the Quaternary. Allele frequency differentiation between the Baltic and Arctic ringed seals, conventionally treated as different subspecies, was weak. Assuming complete isolation, the divergence (F-ST = 0.023) would imply a notably high postglacial effective population size, 20 000 for the Baltic population. The isolation assumption however, seems unrealistic in the light of the data: a coalescent-based simulation approach to the likelihood of alternative demographic histories clearly favoured a scenario with recurrent gene flow to the Baltic, over one of complete isolation (drift only). Within the Baltic Sea, no differentiation was found between the Gulf of Finland and the Gulf of Bothnia breeding areas; the recent population decline and split have not yet affected the inbreeding levels of the disjunct breeding stocks.

Kostia S, Ruohonen-Lehto M, Vainola R, Varvio SL (2000): Phylogenetic information in inter-SINE and inter-SSR fingerprints of the Artiodactyla and evolution of the Bov-tA SINE. Heredity 84: 37-45.

Abstract: Various interspersed repeated sequences and elements (IRSs) can be utilized to generate PCR-based multilocus fingerprint profiles by amplifying the interelement segments, using primers matching the elements themselves. We assessed the utility of inter-IRS fingerprinting in phylogenetic comparisons among six artiodactyl species using several primers derived from two abundant genomic components: the Bov-tA short interspersed nuclear elements (SINEs) and simple sequence repeats or microsatellites (SSRs). Character- and distance-based analyses of the fingerprint data produced trees conforming to the established phylogenetic relationships of species. The strength of phylogenetic signal from different primers varied; combining data from different experiments resulted in robust trees. Within the Cervidae, the hierarchical relationship ((Odocoileus, Rangifer), Alces) was strongly supported. Both methods appear useful tools for systematic studies at time scales < 30 Myr. To elucidate the material basis of inter-SINE fingerprints, we obtained the first sequences of the 'bovid' Bov-tA element also from two cervids (reindeer and white-tailed deer) and analysed their relationship to a number of paralogous bovid elements. The differences among sequences, both intra- and interspecific, were relatively high (mean 18.5%); the sequences showed no clear clustering with the species from which they had been isolated. Most individual elements probably date back to the cervid-bovid ancestor > 25 Myr ago, which is in line with the observed fingerprint distributions.

Vainola R, Kamaltynov RM (1999) Species diversity and speciation in the endemic amphipods of Lake Baikal: molecular evidence. Crustaceana 72: 945-956.

Abstract: The amphipod diversity in the Siberian Lake Baikal is unique, with some 260 endemic species and 80 additional subspecies recognized so far. Three general patterns of differentiation in molecular data, however, suggest that this is still a gross underestimate of the actual number of species. Firstly, allozyme analyses regularly indicate a species-level distinction for taxa previously treated as subspecies there corroborated for Micruropus talitroides / eurypus, M. wahlii / platycercus and Eulimnogammarus verrucosus / oligacanthus). Secondly, so far unrecognized (sibling) species are detected even sympatrically (e.g., in both the Micruropus complexes above). Thirdly, 'conspecific' samples from different parts of the lake, of several Pallasea spp., regularly show diagnostic allozyme differences suggesting presence of vicariant sibling. species in the main geological subdivisions of the basin. Extrapolating the observations to the whole of the Baikalian amphipod fauna, a reasonable projection for the total number may be close to a thousand species.  –  Molecular data suggest that the conventional Baikalian lineages are remarkably old, whereas the vicariant new taxa may have arisen recently in the (early) Pleistocene. These dual levels of diversity are paradoxical in view of the lake's history and the forces supposed to underlie the diversification and speciation processes. The well defined and specialized forms originated in times when the climate and environments were grossly different from the present: not as a response to the present kind of environments. On the other hand, the divergence that has arisen within the time frame of the environmentally modern Lake Baikal (a single basin and cool climate, < 2-3 Myr) appears to be related to geography rather than to adaptive features of morphology and ecology. The patterns prompt a reconsideration of the role of geographical isolation in recent speciation within Lake Baikal.

Väinölä, Risto (1998) A sex-linked locus (Mpi) in the opossum shrimp Mysis relicta: implications for early postglacial colonization history. Heredity 81: 621-629.

Abstract: Strong and persistent associations between sex and genotype frequencies at the Mpi allozyme locus (mannose-6-phosphate isomerase) were found in three lacustrine populations of Mysis relicta sp. I in eastern Finland. Almost all females were homozygotes 100/100, whereas most males were heterozygotes 107/100. This disequilibrium suggests a complete linkage between Mpi and a sex-determining factor in a male heterogametic system and provides the first evidence for a genetic sex-determining mechanism in the crustacean order Mysida. However, no disequilibria were found in other parts of the species range. Potential mechanisms involved in generating the disequilibria are considered (sex-specific selection, recombination modifiers, hitchhiking, population bottlenecks). The restricted geographical distribution of the sex-Mpi association can be related to the early postglacial geological evolution of the lakes studied. A detailed scenario for the colonization history and genetic changes in the populations is presented. This involves initial immigration using temporary connections among ice-marginal lakes in eastern Finland approximately 10000 BP, associated population bottlenecks, and the origin and local selective spread of a nonrecombining Y-Mpi(107) chromosome in the Sotkamo area c. 9300 BP. Soon after the isolation of the three headwater lakes (c. 9100 BP), a new recombination modifier caused a breakdown of the association in populations downstream.

Vainola R, Vainio JK (1998) Distributions, life cycles and hybridization of two Mysis relicta group species (Crustacea, Mysida) in the northern Baltic Sea and Lake Båven. Hydrobiologia 368: 137-148.

Abstract: We used electrophoretically identified material to assess the geographical distributions, life cycles and interspecific hybridization of two sibling species of the Mysis relicta species group (sp. I and sp. II) in the northern Baltic region. In the Gulf of Finland, sp. I prevails in inshore waters and sp. II in the open sea; the distributions overlap in the outer archipelago zone. In the Gulf of Bothnia, only sp. II was found in the southern part (Bothnian Sea), whereas the two species coexist throughout the northerly Bothnian Bay. Both the local and large-scale distributions are salinity-related, but salinity alone does not explain the differences. The two species exhibit different patterns of geographical variation in their life histories. In strict sympatry in the north they have identical two-year life cycles with winter breeding. Further south (Gulf of Finland), sp. I exhibits a predominantly one-year winter-breeding cycle, whereas sp. II breeds throughout the year. The patterns comply with the concept of a great phenotypic flexibility and environmental control of life history characteristics in the Mysis relicta group, and make a contrast to the stable life cycle of the congeneric M. mixta. F1 hybrids between the two M. relicta group species were found at a low frequency (0.6%) in the Bothnian Bay, but not in other areas of sympatry.

Ferris C, King RA, Vainola R, Hewitt GM (1998) Chloroplast DNA recognizes three refugial sources of European oaks and suggests independent eastern and western immigrations to Finland. Heredity 80: 584-593.

Abstract: Refugial differentiation and routes of postglacial migration are major determinants of the patterns of geographical variation we see in natural populations today. We used patterns of chloroplast DNA (cpDNA) variation to investigate the postglacial colonization history of the European oak species Quercus robur and Q. petraea. By sequencing two cpDNA segments using universal primers, we revealed four polymorphic sites which identify four cytotypes with characteristic geographical distributions. Of these, the principal eastern, central and western cytotypes divide the range into three longitudinal zones, each extending from the south to the north of Europe. This corroborates the idea that the postglacial colonization started from three distinct southerly refugia. The fourth cytotype, restricted to East Anglia, was probably derived from the western type postglacially. As a special problem, we addressed the controversial origin of Q. robur at its northern limits in south-western Finland, where it currently occupies a narrow coastal zone disjunct from the remaining oak range. Using a PCR-RFLP assay that discriminates the eastern cytotype, a contact zone of two cytotypes was identified in the region of the Salpausselka ridges. This suggests that the marginal northern occurrence was independently colonized both from the east and from the west, across the Baltic Sea.

Palo J, Varvio SL, Hanski I, Vainola R (1995) Developing microsatellite markers for insect population structure: complex variation in a checkerspot butterfly. Hereditas 123: 295-300.

Abstract: We isolated and characterized two microsatellite markers from the genome of the endangered checkerspot butterfly Melitaea cinxia L. In Finland, this species only survives on the Aland islands, where it exhibits a highly fragmented metapopulation structure on small meadows. Four alleles were observed at the locus CINX1 and nine at CINX4; the total gene diversities at the two loci were H-T = 0.34 and 0.80, respectively. A pilot survey showed moderate gene frequency differentiation among meadows (local populations; F-LM = 0.1) and among metapopulations c. 30 km apart (F-MT = 0.2). Contrary to prior expectation, distinct feeding larval groups collected in the spring did not represent offspring of single females. There was a conspicuous excess of homozygotes within local populations (F-IL = 0.35), which can hardly be attributed to population structure alone; this urges caution in straightforward interpretation of microsatellite phenotype data.

Väinölä Risto (1995) Origin and recent endemic divergence of a Caspian Mysis species flock with affinities to the "glacial relict" crustaceans in boreal lakes. Evolution 49:1215-1223.

Abstract: Aspects of the evolution of intralacustrine species flocks and of the origin of the Arctic or ''glacial-relict'' zoogeographical element in Eurasian inland waters were elucidated in an allozyme study of the crustacean genus Mysis. This element, of supposedly northern marine ancestry, is represented by vicarious taxa in the deeper parts of the Caspian Sea (an enclosed ancient basin) and in young boreal lakes. The three endemic Caspian Mysis species studied are very close genetically (Nei's D = 0.06), which suggests a recent intrabasin radiation and rapid morphological divergence. This is in contrast to the pattern in postglacial Holarctic boreal lakes, where the Mysis relicta group is represented by a set of morphologically uniform but probably much older sibling species (D = 0.3-0.6). The results provide a parallel to those on the recent diversification of some fish species flocks in ancient freshwater lakes. The situation is, however, unusual in that the Caspian sympatric Mysis flock is pelagic, and conditions promoting speciation through allopatric isolation or spatial segregation by trophic substrate specialization seem implausible. The monophyletic Caspian Mysis clade shows a relatively strong divergence from both the northern lacustrine and the Arctic marine congeners (D = 0.6-1.0); the phylogenetic branching order of these three zoogeographical groups is not conclusively resolved. The results contradict the prevailing hypothesis of a recent Pleistocene origin of the Caspian Arctic element by invasion from Eastern European continental proglacial lakes that drained south to the Caspian basin during the glacial maxima and served as refugia for the boreal lacustrine taxa.

Vainola R, Valtonen ET, Gibson DI (1994) Molecular systematics in the acanthocephalan genus Echinorhynchus (sensu lato) in northern Europe. Parasitology 108:105-114.

Abstract: New biological species and high levels of inter- and intraspecific genetic divergence were discovered in an allozyme study of some North European members of the acanthocephalan genus Echinorhynchus (sensu lato), parasites of fish and malacostracan crustaceans. (i) A strong differentiation between the marine E. gadi and the fresh- and brackish-water E. salmonis (genetic identity I ~ 0) supports a generic distinction between these taxa; however, the subdivision would not entirely concur with the concepts of Echinorhynchus (sensu stricto) and Metechinorhynchus suggested earlier. (ii) Samples of E. gadi from the Baltic, Norwegian and North Seas included three distinct, partially sympatric biological species (spp. I-III; I ~ 0.5). (iii) E. bothniensis, previously only known from the northern Baltic Sea, represents a complex of freshwater taxa with an intermediate host relationship to the 'glacial relict'. Mysis spp. and with a distributional and host analogy to the North American E. leidyi. A population in a northern lake in the Barents Sea basin is closely related to E. bothniensis of the Baltic area, but is probably specifically distinct; the divergence between these populations (I ~ 0.6) is similar to that between their Mysis host species. (iv) Considerable intraspecific differentiation (F-ST = 0.25), probably reflecting postglacial population bottlenecks, was found between Baltic and nearby lacustrine E. bothniensis, and between Atlantic and Baltic E. gadi sp. I.

Vainola R, Riddoch BJ, Ward RD, Jones RI (1994) Genetic zoogeography of the Mysis relicta species group (Crustacea: Mysidacea) in northern Europe and North America. Canadian Journal of Fisheries and Aquatic Sciences 51:1490-1505,

Abstract: The zoogeography and systematics of the Mysis relicta species group were elucidated in an allozyme survey of populations across northern Europe and North America. The North American populations are here identified as an independent species (sp. IV), distinct from the three previously recognized European M. relicta group taxa (spp. I-III). The geographical pattern of gene frequency variation in North America supports a late-glacial colonization by separate eastern and western refugial stocks of sp. IV. In Europe, sp. III is known from a single subarctic lake, while both spp. I and II are widespread. They coexist in the Baltic Sea, but their lacustrine distributions are largely different. Species I accounts for most Fennoscandian populations and those in Poland and Germany whereas sp. II lives in Ireland, parts of southwestern Scandinavia, and Karelia. With the paleohydrographical reference, the distributions suggest that both species survived the last glaciation in proglacial lakes east of the Scandinavian Ice. Subsequent distributional differentiation was influenced by environmental variations; the dispersal of sp. II in southwestern Scandinavia was facilitated by a broader euryhalinity than that in sp. I and other stenohaline ''glacial relict'' crustaceans. The Irish populations may represent a distinct refugial stock within sp. II.

Väinölä Risto (1993) Pikkusydänsimpukka Lounais-Suomessa  [Parvicardium hauniense in southwestern Finland]. Luonnon Tutkija 97:33-34.

English summary: Parvicardium hauniense (Petersen & Russel, 1971) (Bivalvia: Cardiidae) is a small cockle only known from the Baltic Sea. It lives on vegetation (e.g. Fucus, Chara) and goes easily confused with young Cerastoderma glaucum, which behaves the same way (although will dig into sediment at later age). In domestic sources, P. hauniense was not previously included in the Finnish fauna. It has now however been recorded both from the Aland islands and from the Archipelago Sea of SW Finland (Hanko, Nauvo). A Finnish common name, pikkusydänsimpukka, is given to the species.

Vainola Risto (1992) Evolutionary genetics of marine Mysis spp. (Crustacea: Mysidacea). Marine Biology 114:539-550.

Abstract: Inter- and intraspecific allozyme differentiation in the mysid crustacean genus Mysis in the North Atlantic region was studied in order to evaluate earlier concepts of evolutionary and systematic relationships and to assess patterns of subdivision within widespread taxa. The results support a relatively ancient divergence of the marine and non-marine species of the genus, and are generally in line with the current subgeneric tridivision into Mysis s.str., Michteimysis and Auricomysis. However, the North American littoral species M. gaspensis should be returned to subgenus Mysis s.str. from its present position in Michteimysis with M. mixta. The closest observed affinities within Mysis s.str. were between M. gaspensis and the freshwater M. relicta group, and between M. oculata and M. litoralis. Intraspecific differentiation among North European coastal populations of M. oculata and M. litoralis was moderately strong (F-ST ~ 0.1), suggesting population bottlenecks and limited dispersal in the post-glacial time. On the other hand, transoceanic differences were not essentially greater, indicating the systematic homogeneity and long-term dispersal capacity in the marine species. This contrasts with the strong genetic and systematic fragmentation earlier found within the circumboreal M. relicta species group.

Vainola R, Hvilsom MM (1991) Genetic divergence and a hybrid zone between Baltic and North Sea Mytilus populations (Mytilidae: Mollusca). Biological Journal of the Linnean Society 43:127-148.

Abstract:Populations of the common mussel (Mytilus edulis) from the North Sea area (Skakerrak-Kattegat) and those from the Baltic Sea are almost diagnostically differentiated at five out of 22 studied allozyme loci; at a further seven loci, alleles predominant or common in one area are nearly absent in the other. Genetic distance was estimated to 0.28; this is similar to the distances of these populations to the Mediterranean mussel M. galloprovincialis. The three mussel types obviously represent equal evolutinary divegence from one another, and should also be taxonomically equally separated; a semispecies rank within a more comprehensive M edulis complex or superspecies is suggested. The age of the Baltic mussel type ('M. trossulus'), as an independent evolutionary lineage, is probably for greater than that of the post-glacial Baltic Sea. Allele frequencies chaning gradually and in parallel when entering from he Kattegat through the Sound into the Baltic. Only a slight Wahlund effect at the strongly diverged Gpi and Pgm loci was found in intermediate populations, indicating that extensive hybridization of the two taxa takes place in the area. However, strong interlocus genotype associations suggest that selection against hybrids is intense in later generations; the c. 100 km wide hybrid zone is narrow relative to the dispersal distance. The genotypic structure of the Lap locus does not conform with those of the other loci studied in the hybrid zone; it cannot be viewed merely as a neutral marker of the process of hybridization.

Vainola R, Rockas H (1990) New distributional data on 'glacial relict' crustaceans. Annales Zoologici Fennici 27:215-220.

Abstract: Earlier reviews on the distribution of the crustaceans Mysis relicta, Pallasea quadrispinosa, Pontoporeia affinis, Gammaracanthus lacustris and Limnocalanus macrurus in Finnish lakes are supplemented with 180 new records, mostly from our field work in 1985-1988. These include records of M. relicta and L. macrurus from Lake Koitere, situated above the highest ancient Baltic shoreline in eastern Finland. The present distribution of G. lacustris, classified as a species in need of monitoring, is reviewed. Some notes on the distribution of these crustaceans outside Finland are also given.

Vainola R, Varvio SL (1989) Biosystematics of Macoma balthica in northwestern Europe. - pp. 309-316 In Ryland, J.S. & Tyler, P.A. (eds.) Reproduction, Genetics and Distributions of Marine Organisms. Olsen & Olsen, Fredensborg.

Abstract: Population differentiation in the infaunal bivalve Macoma balthica was studied with respect to 13 enzyme loci and shell colour phenotypes. Four strongly diverged groups of populations were distinguished, represented by (i) the samples from throughout the Baltic Sea, (ii) those from the North Sea, Kattegat, coasts of Britain and North Norway, (iii) a sample from Varangerfjorden, NE Norway, and (iv) a sample from the St. Lawrence Estuary, Quebec, Canada. The level of differentiation among these four M. balthica types is similar to that among the three taxa of the Mytilus edulis complex in Europe (M. edulis, M. galloprovincialis , and "M. trossulus " of the Baltic). Also the pattern of intergradation between the Baltic and North Sea Macoma populations is similar to that in Mytilus , with some hybridization in the contact zone and introgression over wider distances. We regard the different Macoma types as rather old, independent or semi-independent lineages, which may best be treated as semispecies within the more comprehensive M. balthica complex or superspecies.

Vainola R, Varvio SL (1989) Molecular divergence and evolutionary relationships in Pontoporeia (Crustacea: Amphipoda). Canadian Journal of Fisheries and Aquatic Sciences. 46:1705-1713.

Abstract:  To evaluate hypotheses put forward to explain the origin of the "glacial relict" faunal element in North American and Eurasian lakes, the levels of genetic divergence among species and populations of the amphipod genus Pontoporeia were studied using enzyme electrophoresis. Genetic distances among the European fresh- and brackish-water P. affinis, the North American freshwater P. hoyi, and the marine P. femorata (from Europe) ranged D = 1.5-2.8, suggesting divergence times of the order tens of million years for all these lineages. An undescribed North American coastal species (P. "affinis") was similarly distinct from P. hoyi and P. femorata, but more closely related to the European P. affinis (D = 0.5). No further systematic subdivision within these species was revealed in the examined material. The number of expressed isozyme loci was the same in P. affinis and P. femorata for all enzymes examined; the results provide no support for the hypothesis of a recent polyploidization even in the evolution of P. affinis, as earlier suspected on karyological grounds. All speculations on the role of the late Pleistocene glaciations in molding the currently recognized systematic structure of Pontoporeia were thus dismissed.

Varvio SL, Koehn RK, Vainola R (1988) Evolutionary genetics of the Mytilus edulis complex in the North Atlantic region. Marine Biology 98:51-60.

Genetic relationships among Mytilus populations throughout the North Atlantic region, including the Mediterranean and the Baltic Sea, were studied using enzyme electrophoresis. Three distinct groups of populations, each of a remarkably wide distribution, can be recognised on the basis of their multilocus allelic composition: (1) M. galloprovincialis Lmk. of the Mediterranean and western Europe; (2) a genetically distinct form of M. edulis L. from both the Baltic Sea and some localities in the Canadian Maritime Provinces (here provisionally termed the "trossulus type mussel"); and (3) the traditional "Atlantic" M. edulis populations of northwestern European coasts and most of eastern North America.

Vainola R (1986) Sibling species and phylogenetic relationships of Mysis relicta (Crustacea: Mysidacea). Annales Zoologici Fennici 23:207-221.

Three putative sibling species within Fennoscandian Mysis relicta Loven were detected by biochemical genetic methods (enzyme electrophoresis). Four to seven completely or partially diagnostic loci were found to discriminate each species pair. Genetic distances among the three sibling species, M. mixta and M. litoralis (presumably the closest marine relative of M. relicta) were estimated on the basis of 21 loci.