Population genetic structure of the endangered crayfish Austropotamobius pallipes in France based on microsatellite variation: biogeographical inferences and conservation implications

1. One important goal in conservation biology is to characterise evolutionary lineages within endangered species before management decisions are taken. Here, we assess population differentiation in the freshwater crayfish Austropotamobius pallipes, an endangered species endemic to western Europe and provide valuable information for the conservation of French populations. 2. Analysis of five microsatellite loci in 44 populations revealed very different within population levels of genetic diversity (0.000 < H₀ < 0.564). Two groups, corresponding to northern and southern French populations, showed a high degree of genetic differentiation in both allele frequencies and allele sizes. Comparison of these results with previous studies of A. pallipes strongly suggests that the divergence between northern and southern populations could have occurred during the last glaciation period of the Pleistocene from one Atlantic and one Mediterranean refuge. 3. Evidence for genetic admixture between these two lineages was revealed by correspondence analyses in southern populations, probably as the result of artificial translocations. 4. French populations appeared significantly differentiated among the different river drainages and were highly structured within rivers. The impact of population size, population bottlenecks and founder events on the population genetic differentiation are discussed. 5. Based on these results, we propose the designation of two evolutionarily significant units for A. pallipes in France. Our data also support the maintenance of separate demographic management strategies for crayfish inhabiting different river systems. However, genetic analyses will have to be combined with demographic and ecological data for sustainable conservation programmes.     

Genetic variation of European grayling (Thymallus thymallus) populations in the Western Balkans

In order to elucidate genetic composition of European grayling (Thymallus thymallus) populations in the Western Balkans, the partial mitochondrial DNA (mtDNA) control region was sequenced and 12 microsatellite loci genotyped in 14 populations originating from tributaries of the Adriatic and Danube drainages. Eleven mtDNA haplotypes were found, one confined to the Adriatic clade, one to the Alpine group and the rest to the ‘Balkan’ grayling phylogenetic clade. Haplotypes from the Balkan clade were confined to the Danube drainage and constituted two groups: northern group with haplotypes found in the Slovenian part of the Danube drainage, and southern group, consisting from Bosnia–Herzegovina and Montenegro. Substantial genetic distance between northern and southern groups of haplotypes (0.75–1.8%) and well supported divisions within the northern group indicate very structured grayling population within the studied Danube basin that most probably did not evolve due to vicariance but rather as a consequence of multiple colonization waves that might have occurred during the Pleistocene. Furthermore, genetic distance of ~4% between Adriatic and Danube populations’ haplotypes, suggest that their separation occurred in mid-Pliocene. These findings imply a complex colonization pattern of the Western Balkans drainages. Microsatellite data also confirm high genetic diversity in Western Balkans populations of grayling (on average 7.5 alleles per microsatellite locus and H _exp 0.58). Limited stocking activities were detected based on microsatellites and mtDNA data. Regarding current knowledge of grayling phylogeography appropriate management strategies were proposed to preserve unique, autochthonous grayling populations in Western Balkan.     

Genetic lineages and postglacial colonization of grayling (Thymallus thymallus, Salmonidae) in Europe, as revealed by mitochondrial DNA analyses

In stark contrast to other species within the Salmonidae family, phylogeographic information on European grayling, Thymallus thymallus, is virtually nonexistent. In this paper, we utilized mitochondrial DNA polymerase chain reaction-restriction fragment length polymorphism (mtDNA PCR-RFLP) and sequence variation to infer the postglacial dispersal routes of T. thymallus into and within northern Europe, and to locate geographically, potential evolutionarily distinct populations. Mitochondrial analyses revealed a total of 27 T. thymallus haplotypes which clustered into three distinct lineages. Average pairwise interlineage divergence was four and nine times higher than average intralineage divergence for RFLP and sequence data, respectively. Two European grayling individuals from the easternmost sample in Russia exhibited haplotypes more genetically diverged from any T. thymallus haplotype than T. arcticus haplotype, and suggested that hybridization/introgression zone of these two sister species may extend much further west than previously thought. Geographic division of the lineages was generally very clear with northern Europe comprising of two genetically differentiated areas: (i) Finland, Estonia and north-western Russia; and (ii) central Germany, Poland and western Fennoscandia. Average interpopulation divergence in North European T. thymallus was 10 times higher than that observed in a recent mtDNA study of North American T. arcticus. We conclude that (i) North European T. thymallus populations have survived dramatic Pleistocene temperature oscillations and originate from ancient eastern and central European refugia; (ii) genetic divergence of population groups within northern Europe is substantial and geographically distinct; and (iii) the remainder of Europe harbours additional differentiated assemblages that likely descend from a Danubian refugium. These findings should provide useful information for developing appropriate conservation strategies for European grayling and exemplify a case with a clear need for multinational co-operation for managing and conserving biodiversity.     

Microsatellite data resolve phylogeographic patterns in European grayling, Thymallus thymallus, Salmonidae

The phylogeography of an endangered salmonid, European grayling (Thymallus thymallus), was studied based on analysis of 17 nuclear microsatellite DNA loci. In agreement with earlier mitochondrial DNA (mtDNA) studies, phylogenetic relationships of the populations suggested that northern Europe was colonized from two distinct Pleistocene refugia. Furthermore, microsatellites revealed highly supported grouping of mainland Swedish, Norwegian, Danish, German and Slovenian populations, suggesting that grayling from the northwestern and central Europe have descended from their southern conspecifics. The level of divergence between populations was substantial, even across short geographical distances. Although this was in part due to postglacial colonization patterns and contemporary barriers for gene flow, the high divergence estimates between hydrologically connected sampling locations implied efficient interpopulation reproductive isolation. Microsatellites revealed that the populations exhibited, on average, only 3.5 (+/-2.2) alleles per locus, indicating that T. thymallus has strikingly low levels of intrapopulation genetic diversity as compared with other freshwater fish species. Accordingly, as indicated by analysis of molecular variance (AMOVA), only 49.1-58.0% of the total grayling microsatellite diversity resided within populations. A latitudinal genetic diversity gradient, potentially resulting from glaciation-mediated founder events, was not evident. Alternatively, it is possible that grayling display limited dispersal behaviour/capability, leading to low long-term effective population sizes and, consequently, depauperate intrapopulation polymorphism. These findings have implications for conservation of T. thymallus. Importantly, they exemplify that microsatellites can be highly informative for intraspecific phylogeography studies dealing with substantial divergence scales.     

Genetic differentiation of European grayling populations across the Main, Danube and Elbe drainages in Bavaria

Analysis of mitochondrial ( ND-1/3/4 genes) and nuclear ( GH-1 gene, four microsatellite loci) DNA markers of European grayling Thymallus thymallus populations identified strong genetic differentiation between the Rhine/Main, Elbe and Danube drainages in Bavaria, as a result of both present processes and past history. The Danube and the Main-Elbe group diverged about five times earlier than the populations of Main and Elbe. These data suggest that exchange and transfer of grayling stocking material between these drainages should be avoided, to maintain the genetic diversity and integrity of populations.     

Phylogenetic analysis of the genus Thymallus (grayling) based on mtDNA control region and ATPase 6 genes, with inferences on control region constraints and broad-scale Eurasian phylogeography

We present first insights into the molecular phylogeny of the grayling genus Thymallus (Salmonidae) using sequences from the mitochondrial control region and ATPase6 genes. A suite of analytical approaches were applied for each gene separately and for the combined data. The ATPase6 gene is shown to have a mean divergence rate across the genus of 2.46 times faster than the complete control region. Based on the combined data, four major (internal) clades, presumably originating in the Pliocene, were resolved with high support in all analyses and represented two distinct lineages in the Amur basin, one lineage in all remaining Siberian and Mongolian drainages, and one lineage corresponding to European grayling Thymallus thymallus. The resolution of multiple lineages, from both additional internal and terminal clades, within each major drainage basin underscores the complexity and effects that Pleistocene hydrological dynamics have had on the distribution of biodiversity in Siberia.     

Discriminating the impact of recent human mediated stock transfer from historical gene flow on genetic structure of European grayling Thymallus thymallus L.

Microsatellite markers were first used to partition individuals of European grayling Thymallus thymallus , from the Danube, Rhine and Main, and Elbe drainage systems into subpopulations and to estimate individual immigrant ancestries over the last few generations. Subsequently, the studied populations were 'purged' from recent immigrants and the proportions of evolutionary lineages within the 'purged' populations were re-estimated by applying mtDNA markers. The results confirmed a high level of admixture of the divergent mtDNA lineages ( i.e. natural secondary contact) in populations sampled at the contact zones of the drainages. In addition, a substantial amount of introgression was observed for several populations that were known to be affected by stocking of European grayling from different origins.     

Genetic introgression between wild and stocked salmonids and the prospects for using molecular markers in population rehabilitation: the case of the Adriatic grayling (Thymallus thymallus L. 1785)

In the north Adriatic basin, a morphologically and genetically distinct lineage of grayling is found, designated as the Adriatic grayling. In Slovenia, the Adriatic grayling is restricted to the Soca river system, where it is critically endangered. The most pertinent threat is stocking with non-native, highly divergent Sava (Danubian) drainage stock, and this activity has been going on for more than four decades. The present study was designed to characterise the genetic structure of the Adriatic grayling in Slovenia, with particular emphasis on estimating the degree of introgression with non-indigenous stocked grayling. We analysed polymorphism at 154 microsatellite loci in samples representing grayling from the Adriatic and Danubian drainage stock. A relatively high number (12) of alleles, diagnostic for the Adriatic grayling, were identified. However, a correspondence analysis based on individual multilocus genotypes also revealed that there is no distinctive Adriatic group but rather a dispersed multitude of individuals that cannot be unambiguously distinguished from the more homogenous Danubian population. A Bayesian analysis of individual admixture coefficients confirmed this pattern and revealed extensive introgression between the Adriatic grayling and stocked grayling of Danubian origin. Average individual admixture coefficients showed that only between 50 and 60% of the original gene pools remained, and only few non-introgressed indigenous individuals could be identified. Microsatellite-based individual admixture analysis appear to be an important tool for identifying remaining non-introgressed indigenous individuals that could be used for restoring the original populations.     

Phylogeographical lineages of Arctic grayling (Thymallus arcticus) in North America: divergence, origins and affinities with Eurasian Thymallus

The number and location of Arctic glacial refugia utilized by taxa during the Pleistocene are continuing uncertainties in Holarctic phylogeography. Arctic grayling (Thymallus arcticus) are widely distributed in freshwaters from the eastern side of Hudson Bay (Canada) west to central Asia. We studied mitochondrial DNA (mtDNA) and microsatellite DNA variation in North American T. arcticus to test for genetic signatures of survival in, and postglacial dispersal from, multiple glacial refugia, and to assess their evolutionary affinities with Eurasian Thymallus. In samples from 32 localities, we resolved 12 mtDNA haplotypes belonging to three assemblages that differed from each other in sequence by between 0.75 and 2.13%: a 'South Beringia' lineage found from western Alaska to northern British Columbia, Canada; a 'North Beringia' lineage found on the north slope of Alaska, the lower Mackenzie River, and to eastern Saskatchewan; and a 'Nahanni' lineage confined to the Nahanni River area of the upper Mackenzie River drainage. Sequence analysis of a portion of the control region indicated monophyly of all North American T. arcticus and their probable origin from eastern Siberian T. arcticus at least 3 Mya. Arctic grayling sampled from 25 localities displayed low allelic diversity and expected heterozygosity (H(E)) across five microsatellite loci (means of 2.1 alleles and 0.27 H(E), respectively) and there were declines in these measures of genetic diversity with distance eastward from the lower Yukon River Valley. Assemblages defined by mtDNA divergences were less apparent at microsatellite loci, but again the Nahanni lineage was the most distinctive. Analysis of molecular variance indicated that between 24% (microsatellite DNA) and 81% (mtDNA) of the variance was attributable to differences among South Beringia, North Beringia and Nahanni lineages. Our data suggest that extant North American Arctic grayling are more diverse phylogeographically than previously suspected and that they consist of at least three major lineages that originated in distinct Pleistocene glacial refugia. T. arcticus probably originated and dispersed from Eurasia to North America in the late to mid-Pliocene, but our data also suggest more recent (mid-late Pleistocene) interactions between lineages across Beringia.     

Molecular data and species distribution models reveal the Pleistocene history of the mayfly Ameletus inopinatus (Ephemeroptera: Siphlonuridae)1

1. We investigated the Pleistocene and Holocene history of the rare mayfly Ameletus inopinatus EATON 1887 (Ephemeroptera: Siphlonuridae) in Europe. We used A. inopinatus as a model species to explore the phylogeography of montane, cold‐tolerant aquatic insects with arctic–alpine distributions. 2. Using species distribution models, we developed hypotheses about the species demographic history in Central Europe and the recolonisation history of Fennoscandia. We tested these hypotheses using mitochondrial cytochrome oxidase I (mtCOI) sequence data and compared our genetic results with previously generated microsatellite data to explore genetic diversity distributions of A. inopinatus. 3. We observed old lineages, deep splits and almost complete lineage sorting of mtCOI sequences among mountain ranges. These results support a periglacial survival, i.e. persistence at the periphery of Pleistocene glaciers in Central Europe. 4. There was strong differentiation between the Fennoscandian and all other populations, indicating that Fennoscandia was recolonised from a refugium not accounted for in our sampling. High degrees of population genetic structure within the northern samples suggest that Fennoscandia was recolonised by more than one lineage. However, this structure was not apparent in previously published microsatellite data, consistent with secondary contact without sexual incompatibility or with sex‐biased dispersal. 5. Our demographic analyses indicate that (i) the separation of northern and Central European lineages occurred during the early Pleistocene; (ii) Central European populations have persisted independently throughout the Pleistocene and (iii) the species extended its range about 150 000 years ago.     

History vs. habitat type: explaining the genetic structure of European nine‐spined stickleback (Pungitius pungitius) populations

The genetic structure of contemporary populations can be shaped by both their history and current ecological conditions. We assessed the relative importance of postglacial colonization history and habitat type in the patterns and degree of genetic diversity and differentiation in northern European nine‐spined sticklebacks (Pungitius pungitius), using mitochondrial DNA (mtDNA) sequences and 12 nuclear microsatellite and insertion/deletion loci. The mtDNA analyses identified – and microsatellite analyses supported – the existence of two historically distinct lineages (eastern and western). The analyses of nuclear loci among 51 European sites revealed clear historically influenced and to minor degree habitat dependent, patterns of genetic diversity and differentiation. While the effect of habitat type on the levels of genetic variation (coastal > freshwater) and differentiation (freshwater > coastal) was clear, the levels of genetic variability and differentiation in the freshwater sites were independent of habitat type (viz. river, lake and pond). However, levels of genetic variability, together with estimates of historical effective population sizes, decreased dramatically and linearly with increasing latitude. These geographical patterns of genetic variability and differentiation suggest that the contemporary genetic structure of freshwater nine‐spined sticklebacks has been strongly impacted by the founder events associated with postglacial colonization and less by current ecological conditions (cf. habitat type). In general, the results highlight the strong and persistent effects of postglacial colonization history on genetic structuring of northern European fauna and provide an unparalleled example of latitudinal trends in levels of genetic diversity.     

Molecular phylogeography of the viperine snake Natrix maura (Serpentes: Colubridae): Evidence for strong intraspecific differentiation

The molecular phylogeography of the viperine snake, Natrix maura (Linnaeus, 1758), was investigated using complete sequences of the mitochondrial cytochrome b gene and genomic ISSR-PCR fingerprinting. In a total of 120 samples, 44 unique cytochrome b haplotypes were found which defined three major genetic lineages associated with samples from Morocco, Tunisia and Europe, respectively. The same lineages were supported by nuclear data. A possible fourth lineage exists in southern Spain. Genetic distances of cytochrome b sequences between the three main lineages were in the range of 3.9–5.6%, suggesting independent evolution since the early Pliocene. Distinction of the three major lineages at the subspecies or species level is discussed to account taxonomically for the high intraspecific variation in the viperine snake. A more detailed analysis of the European samples based on genetic diversity indices and a network reconstruction suggests a complex Pleistocene history for the viperine snake in Europe. Clear differentiation was found between populations south and north of the central Iberian mountain ranges, suggesting Pleistocene glacial refugia both in the southern and northern Iberian peninsula. In the south, genetic diversity was associated with the main river valleys, whereas northern haplotypes were more broadly distributed, indicating gene flow or postglacial range expansions. Unexpectedly high levels of genetic variation in southeastern France and northwestern Italy would be compatible with the hypothesis of a glacial refugium north of the Pyrenees or in Italy. However, due to the dependence of N. maura on warm climates, the assumption of a northern refugium seems unwarranted. We believe that further sampling in northern Spain is likely to reveal genetically diverse populations which could have served as sources for postglacial recolonization of France and Italy.     

Genetic diversity and differentiation of central European freshwater pearl mussel (Margaritifera margaritifera L.) populations: implications for conservation and management

Despite the fact that mollusc species play an important role in many aquatic ecosystems, little is known about their biodiversity and conservation genetics. Freshwater pearl mussel (Margaritifera margaritifera L.) populations are seriously declining all over Europe and a variety of conservation programs are being established to support the remaining endangered central European populations. In order to provide guidelines for conservation strategies and management programs, we investigated the genetic structure of 24 freshwater pearl mussel populations originating from five major central European drainages including Elbe, Danube, Rhine, Maas and Weser, representing the last and most important populations in this area. We present a nondestructive sampling method of haemolymph for DNA analyses, which is applicable for endangered bivalves. The analyses of nine microsatellite loci with different levels of polymorphism revealed a high degree of fragmented population structure and very different levels of genetic diversity within populations. These patterns can be explained by historical and demographic effects and have been enforced by anthropogenic activities. Even within drainages, distinct conservation units were detected, as revealed from high F(ST) values, private alleles and genetic distance measures. Populations sampled close to contact zones between main drainage systems showed lowest levels of correct assignment to present-day drainage systems. Populations with high priority for conservation should not only be selected by means of census population size and geographical distance to other populations. Instead, detailed genetic analyses are mandatory for revealing differentiation and diversity parameters, which should be combined with ecological criteria for sustainable conservation and recovery programs.     

Genetic analysis of southern African gemsbok (Oryx gazella) reveals high variability, distinct lineages and strong divergence from the East African Oryx beisa

We carried out a population genetic analysis of five southern African gemsbok (Oryx gazella) populations based on 530 bp of the mitochondrial control region and ten microsatellites in 75 individuals. Both markers show the high variability often observed in African bovids. Three of the populations which can be traced back to very small founding or current sizes do not show any signs of reduced variability compared to the remaining populations. The mitochondrial haplotypes form three distinct lineages which most likely originated in the Pleistocene when climate fluctuations led to periodical reduction and spreading of gemsbok habitat and which, today, are found throughout the distribution range. Bayesian microsatellite analyses yielded two groups, suggesting a more recent geographical differentiation following the admixture of the mtDNA lineages. Combining our sequences with available published data of the remaining oryx species allowed for a direct molecular comparison of O. gazella and O. beisa which have sometimes been considered a single species. The average genetic divergence between haplotypes from the two taxa was very high (39.9%), supporting their classification into two different species.     

Microsatellite variation in Bavarian populations of European grayling (Thymallus thymallus): Implications for conservation

European grayling populations in Bavaria have shown steady declines during the last 10–20years. In order to provide guidelines for conservation strategies and future management programs, we investigated the genetic structure of 15 grayling populations originating from three major Central European drainages (the Danube, the Elbe and the Rhine/Main) using 20 microsatellite loci. Genetic divergence between the three drainage systems was substantial as illustrated by highly significant heterogeneity of genotype frequencies, high number of drainage-specific private alleles, high between-drainage F _ST values, high assignment success of individuals to their drainage of origin and the high bootstrap support for the genetic distance based drainage-specific population clusters. In agreement with earlier studies, microsatellites revealed relatively low levels of intrapopulational genetic diversity in comparison to the overall level of variation across populations. Maximum likelihood methods using the coalescent approach revealed that the proportion of common ancestors was generally high in native populations and that the estimates of N _e were correlated with the genetic diversity parameters in all drainages. The number of effective immigrants per generation (N _e m) was less than one for all pairwise comparisons of populations within the drainages, indicating restricted interpopulational gene flow. Based on these findings we recommend a drainage and sub-drainage specific conservation of grayling populations in order to preserve their overall genetic diversity and integrity. For large-scale stocking actions to supplement declining or to restore extinct populations, creation of separate broodstocks for major conservation units (ESUs and MUs) is warranted. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phylogenetic Relationships within GenusLeuciscus(Pisces, Cyprinidae) in Portuguese Fresh Waters, Based on Mitochondrial DNA CytochromebSequences

To investigate phylogenetic relationships amongLeuciscusspecies occurring in Portuguese inland waters, the cytochromebgene was sequenced from representatives of the main rivers. This study supports the recognition of the species level forL. pyrenaicus,including populations from the southern Portuguese drainages (Tejo, Sado, and Guadiana drainages), and forL. carolitertii,including populations from the northern Portuguese drainages. The existence of two new species occurring in the extreme southwestern drainages of Mira and Arade is also suggested. The present results support the monophyly of the Mira and the Arade populations, as well as an early divergence of these two lineages. The present-day distribution ofLeuciscusspecies is seen as a consequence of Pliocene and Pleistocene events, such as river disjunctions and posterior confluence in epicontinental seas and river captures. A mixture of haplotypes was observed in the Mondego and the Tejo drainages, which could be a consequence of ancient river captures, with a possible mitochondrial DNA introgression in the Tejo drainage and a recent introduction by man in the Mondego drainage. The pattern of differentiation among mtDNA haplotypes and their geographic distribution is discussed in terms of evolutionary aspects.     

Genetic divergence and phylogeographic relationships among european perch (Perca fluviatilis) populations reflect glacial refugia and postglacial colonization

We used the widely distributed freshwater fish, perch (Perca fluviatilis), to investigate the postglacial colonization routes of freshwater fishes in Europe. Genetic variability within and among drainages was assessed using mitochondrial DNA (mtDNA) D-loop sequencing and RAPD markers from 55 populations all over Europe as well as one Siberian population. High level of structuring for both markers was observed among drainages and regions, while little differentiation was seen within drainages and regions. Phylogeographic relationships among European perch were determined from the distribution of 35 mtDNA haplotypes detected in the samples. In addition to a distinct southern European group, which includes a Greek and a southern Danubian population, three major groups of perch are observed: the western European drainages, the eastern European drainages including the Siberian population, and Norwegian populations from northern Norway, and western side of Oslofjord. Our data suggest that present perch populations in western and northern Europe were colonized from three main refugia, located in southeastern, northeastern and western Europe. In support of this, nested cladistic analysis of mtDNA clade and nested clade distances suggested historical range expansion as the main factor determining geographical distribution of haplotypes. The Baltic Sea has been colonized from all three refugia, and northeastern Europe harbours descendants from both eastern European refugia. In the upper part of the Danube lineages from the western European and the southern European refugia meet. The southern European refugium probably did not contribute to the recolonization of other western and northern European drainages after the last glaciation. However, phylogenetic analyses suggest that the southern European mtDNA lineage is the most ancient, and therefore likely to be the founder of all present perch lineages. The colonization routes used by perch probably also apply to other freshwater species with similar distribution patterns.     

多基因联合揭示海南鲌的遗传结构与遗传多样性

海南鲌(Culter recurviceps)是我国华南地区重要经济鱼类, 由于受到近些年水利开发、过度捕捞、环境污染等诸多因素的影响, 其资源量快速下降, 亟需得到更多的关注和保护。为保护和合理开发海南鲌种质资源, 本研究采集了华南地区23个地理群体207尾海南鲌样本, 测定了2个线粒体基因(Cytb和ND2)并从Barcode of Life Data System数据库获得相对应线粒体COI基因, 结合多种分析方法(系统发育分析、分化时间估算、单倍型网状图、群体遗传分析和Mantel检验)对海南鲌的遗传结构和遗传多样性展开研究。系统发育分析和单倍型网状图表明华南地区海南鲌群体被分成3个谱系(I、II和III), 其中谱系I和III由珠江的群体组成, 谱系II由海南岛的群体组成。分化时间估算发现3个谱系之间的分化时间介于0.028-0.251 Ma之间, 表明华南地区更新世气候变化可能是造成海南鲌谱系分化的重要原因。群体遗传分析发现海南鲌群体之间存在极显著的遗传分化(F_ST = 0.511, P < 0.001), 并且符合距离隔离模式(R = 0.348, P = 0.0010)。群体动态历史分析表明, 海南鲌群体可能在0.010-0.025 Ma经历了群体扩张, 表明更新世的气候波动也影响了海南鲌的群体大小和分布。综上所述, 海南鲌群体由3个谱系组成, 更新世气候变化是导致3个谱系分化和影响海南鲌群体动态历史的重要因素。此外, 海南鲌群体之间的遗传分化也可能受到了空间距离的影响。     

Pleistocene effects on the European freshwater fish fauna: double origin of the cobitid genus Sabanejewia in the Danube basin (Osteichthyes: Cobitidae)

Biogeographical hypotheses of European freshwater fishes were inferred using phylogeographic analysis of the complete cytochrome b and ATP synthase 8 and 6 mitochondrial genes (1982bp). To test the relative importance of drainage origin versus Pleistocene glaciations in the origin of primary freshwater fishes in Europe, we reconstructed the phylogenetic relationships of the genus Sabanejewia which is distributed in European waters. The phylogenetic relationships recovered for the genus Sabanejewia (n=75) provide support for the monophyly of six main evolutionary mtDNA lineages: Sabanejewia larvata, Sabanejewia romanica, Sabanejewia aurata/Sabanejewia caucasica, Sabanejewia kubanica, Sabanejewia baltica, and the Danubian-Balkanian complex. The Caucasian-Caspian mtDNA lineages, S. kubanica, S. aurata/S. caucasica, and the Northern European S. baltica represents the sister group of the Danubian-Balkanian complex mtDNAclade, supporting a Caucasian-Northern European origin of most of mtDNA lineages of the Central European freshwater fish fauna. The mtDNA divergence observed between the Danubian Sabanejewia species is too dissimilar to support their contemporary origin. Rather, the mtDNA data suggest that the Danubian Sabanejewia lineages most likely have a double origin, indicating that the European Sabanejewia lineages have experienced different historical processes for the following reasons. First, the origin of the S. larvata and S. romanica mtDNA clades predates the origin of the Danubian-Balkanian complex, and our results showed that the completion of the Alps and the origin of the Danube drainage seem to have promoted the speciation of the earliest Sabanejewia clades in the Miocene. Second, small genetic distances and the geographical pattern found within the Danubian-Balkanian complex clade indicate that the lineages included in this clade spread recently across the Danube and Greek river drainages. The inclusion of the S. balcanica species within all mtDNA lineages suggests that cyclical cold periods during the Pleistocene glaciations have favoured its rapid expansion and genetic homogenisation across Central European and Greek waters.     

Geographical and Ecological Drivers of Mitonuclear Genetic Divergence in a Mediterranean Grasshopper

The study of the neutral and/or selective processes driving genetic variation in natural populations is central to determine the evolutionary history of species and lineages and understand how they interact with different historical and contemporary components of landscape heterogeneity. Here, we combine nuclear and mitochondrial data to study the processes shaping genetic divergence in the Mediterranean esparto grasshopper (Ramburiella hispanica). Our analyses revealed the presence of three main lineages, two in Europe that split in the Early-Middle Pleistocene and one in North Africa that diverged from the two European ones after the Messinian. Lineage-specific potential distribution models and tests of environmental niche differentiation suggest that the phylogeographic structure of the species was driven by allopatric divergence due to the re-opening of the Gibraltar strait at the end of the Messinian (Europe–Africa split) and population fragmentation in geographically isolated Pleistocene climatic refugia (European split). Although we found no evidence for environment as an important driver of genetic divergence at the onset of lineage formation, our analyses considering the spatial distribution of populations and different aspects of landscape composition suggest that genetic differentiation at mitochondrial loci was largely explained by environmental dissimilarity, whereas resistance-based estimates of geographical distance were the only predictors of genetic differentiation at nuclear markers. Overall, our study shows that although historical factors have largely shaped concordant range-wide patterns of mitonuclear genetic structure in the esparto grasshopper, different contemporary processes (neutral gene flow vs. environmental-based selection) seem to be governing the spatial distribution of genetic variation in the two genomes.