The role of western Mediterranean islands in the evolutionary diversification of the spotted flycatcher Muscicapa striata,a long‐distance migratory passerine species

We investigated the evolutionary history of the spotted flycatcher Muscicapa striata, a long distance migratory passerine having a widespread range, using mitochondrial markers and nuclear introns. Our mitochondrial results reveal the existence of one insular lineage restricted to the western Mediterranean islands (Balearics, Corsica, Sardinia) and possibly to the Tyrrhenian coast of Italy that diverged from the mainland lineages around 1 Mya. Mitochondrial genetic distance between insular and mainland lineages is around 3.5%. Limited levels of shared nuclear alleles among insular and mainland populations further support the genetic distinctiveness of insular spotted flycatchers with respect to their mainland counterparts. Moreover, lack of mitochondrial haplotypes sharing between Balearic birds (M. s. balearica) and Corso‐Sardinian birds (M. s. tyrrhenica) suggest the absence of recent matrilineal gene flow between these two insular subspecies. Accordingly, we suggest that insular spotted flycatchers could be treated as one polytypic species (Muscicapa tyrrhenica) that differs from M. striata in morphology, migration, mitochondrial and nuclear DNA and comprises two subspecies (the nominate and M. t. balearica) that diverged recently phenotypically and in mitochondrial DNA and but still share the same nuclear alleles. This study provides an interesting case‐study illustrating the crucial role of western Mediterranean islands in the evolution of a passerine showing high dispersal capabilities. Our genetic results highlight the role of glacial refugia of these islands that allowed initial allopatric divergence of insular populations. We hypothesize that differences in migratory and breeding phenology may prevent any current gene flow between insular and mainland populations of the spotted flycatcher that temporarily share the same insular habitats during the spring migration.     

Is it worth eradicating the invasive pest Rattus norvegicus from Molène archipelago? Genetic structure as a decision-making tool

Genetic variability and structure were estimated by microsatellite analysis at 7 loci in brown rat populations (Rattus norvegicus) from the Iroise insular complex and neighbouring mainland (Brittany, France). Island genetic diversity is lower than on the mainland and a highly significant positive correlation was found between mean heterozygosity and the logarithm of island area, which is consistent with theoretical expectations. Rattus norvegicus populations are substructured at a kilometric scale, both on the islands and on the mainland. Intra-island structuration is extremely high, suggesting that no effective migration occurs between islands or with the mainland. Historical and genetical evidence suggest that R. norvegicus was introduced independently on Ouessant and Molène archipelago, with a low and a high founder effect respectively. These results are discussed in terms of recolonization probability of islands that have been cleared of R. norvegicus, which illustrates the usefulness of genetic markers in determining parameters of interest to the conservation biologist.     

Potential for higher invasiveness of the alien Oxalis pes-caprae on islands than on the mainland

The higher vulnerability of islands to invasions compared to mainland areas has been partially attributed to a simplification of island communities, with lower levels of natural enemies and competitors on islands conferring vacant niches for invaders to establish and proliferate. However, differences in invader life-history traits between populations have received less attention. We conducted a broad geographical analysis (i.e. 1050 km wide transect) of plant traits comparing insular and mainland populations to test the hypothesis that alien plants from insular populations have the potential for higher invasiveness than their alien mainland counterparts. For this purpose plants of the annual geophyte Oxalis pes-caprae were grown from bulbs collected in the Balearic islands and the Spanish mainland under common greenhouse conditions. There were no significant differences in bulb emergence and plant survival between descendants from insular and mainland populations. However, Oxalis descendants from insular populations produced 20% more bulbs without reducing allocation to bulb size, above-ground biomass or flowering than descendants from mainland populations. Based on the lack of sexual reproduction in Oxalis and the dependence of invasion on bulb production, our study suggests that the higher occurrence of Oxalis in the Balearic islands than in the Spanish mainland can partially be explained by genetically based higher propagation potential of insular populations compared to mainland populations.     

A nuclear perspective on endemism in northern flying squirrels (Glaucomys sabrinus) of the Alexander Archipelago, Alaska

We used microsatellites to examine populationstructure and genetic diversity in northernflying squirrels in the Alexander Archipelagoof Southeast Alaska, with an emphasis on theendemic Prince of Wales flying squirrel(Glaucomys sabrinus griseifrons). Previouswork showed this subspecific designationcoincided with a distinct mitochondrial lineageon eleven islands (the Prince of Wales [POW]complex). To obtain a nuclear perspective onthis lineage and to further investigate geneticdiversity among insular populations, weexamined six microsatellite loci in 233 flyingsquirrels representing eight populations inSoutheast Alaska and a population from interiorAlaska (seven island and two mainlandlocalities). Island populations have lowerheterozygosity and allelic diversity thanmainland populations. Overall, populationpairs show a pattern of isolation by distance,indicating there is little long-distance geneflow across the archipelago. Analyses ofmicrosatellite allele frequencies revealsignificant differences between the POW complexpopulations and others we examined, a findingcongruent with the mitochondrial data. Thepopulation from Mitkof Island, a non-POWcomplex island, also differs significantly fromother populations in allele frequencies. Thesix POW complex populations are geneticallyvery similar, suggesting current or recent geneflow among these islands, while there seems tobe no gene flow between the POW complex andother populations in Southeast Alaska. Ourdata corroborate mitochondrial DNA resultsindicating that G. s. griseifrons isgenetically distinct and suggest a generalpattern of isolation of insular flyingsquirrels in Southeast Alaska.     

Population size and time since island isolation determine genetic diversity loss in insular frog populations

Understanding the factors that contribute to loss of genetic diversity in fragmented populations is crucial for conservation measurements. Land‐bridge archipelagoes offer ideal model systems for identifying the long‐term effects of these factors on genetic variations in wild populations. In this study, we used nine microsatellite markers to quantify genetic diversity and differentiation of 810 pond frogs (Pelophylax nigromaculatus) from 24 islands of the Zhoushan Archipelago and three sites on nearby mainland China and estimated the effects of the island area, population size, time since island isolation, distance to the mainland and distance to the nearest larger island on reduced genetic diversity of insular populations. The mainland populations displayed higher genetic diversity than insular populations. Genetic differentiations and no obvious gene flow were detected among the frog populations on the islands. Hierarchical partitioning analysis showed that only time since island isolation (square‐root‐transformed) and population size (log‐transformed) significantly contributed to insular genetic diversity. These results suggest that decreased genetic diversity and genetic differentiations among insular populations may have been caused by random genetic drift following isolation by rising sea levels during the Holocene. The results provide strong evidence for a relationship between retained genetic diversity and population size and time since island isolation for pond frogs on the islands, consistent with the prediction of the neutral theory for finite populations. Our study highlights the importance of the size and estimated isolation time of populations in understanding the mechanisms of genetic diversity loss and differentiation in fragmented wild populations.     

Genetic diversity of insular natural populations of <Emphasis Type="Italic">Festuca pratensis</Emphasis> Huds.: RAPD analysis

In natural populations of Festuca pratensis Huds. from the islands of Onega Lake, the level of genetic diversity was evaluated. In three populations variability of 64 RAPD loci was tested. The level of genetic diversity (P _95% = 30.2; H _exp = 0.093) was low for a cross-pollinating plant species. Furthermore, genetic similarity between the plants from insular populations was found to be high (I _N = 0.887). It was demonstrated that genetic variation among the population accounted for at most 5.3% of total genetic diversity, which, however, was higher than the F _ST values for continental populations (F _ST = 0.022). It was suggested that specific features of the genetic structure of insular population, i.e., low gene diversity within the populations along with high differentiation among the populations, were caused by the gene flow attenuation, as a result of isolation, and intensification of inbreeding. These features had negative effect on total population adaptation.     

Multilocus genetic diversity and historical biogeography of the endemic wall lizard from Ibiza and Formentera,Podarcis pityusensis (Squamata: Lacertidae)

Two monophyletic sister species of wall lizards inhabit the two main groups of Balearic Islands: Podarcis lilfordi from islets and small islands around Mallorca and Menorca and Podarcis pityusensis from Ibiza, Formentera and associated islets. Genetic diversity within the endangered P. lilfordi has been well characterized, but P. pityusensis has not been studied in depth. Here, 2430 bp of mtDNA and 15 microsatellite loci were analysed from P. pityusensis populations from across its natural range. Two main genetic groupings were identified, although geographical structuring differed slightly between the mtDNA and the nuclear loci. In general, individuals from islets/islands adjacent to the main island of Ibiza were genetically distinct from those from Formentera and the associated Freus islands for both mtDNA and the nuclear loci. However, most individuals from the island of Ibiza were grouped with neighbouring islets/islands for nuclear loci, but with Formentera and Freus islands for the mitochondrial locus. A time‐calibrated Bayesian tree was constructed for the principal mitochondrial lineages within the Balearics, using the multispecies coalescent model, and provided statistical support for divergence of the two main P. pityusensis lineages 0.111–0.295 Ma. This suggests a mid‐late Pleistocene intraspecific divergence, compared with an early Pleistocene divergence in P. lilfordi, and postdates some major increases in sea level between 0.4 and 0.6 Ma, which may have flooded Formentera. The program IMa2 provided a posterior divergence time of 0.089–0.221 Ma, which was similar to the multispecies coalescent tree estimate. More significantly, it indicated low but asymmetric effective gene copy migration rates, with higher migration from Formentera to Ibiza populations. Our findings suggest that much of the present‐day diversity may have originated from a late Pleistocene colonization of one island group from the other, followed by allopatric divergence of these populations. Subsequent gene flow between these insular groups seems likely to be explained by recent human introductions. Two evolutionary significant units can be defined for P. pityusensis but these units would need to exclude the populations that have been the subjects of recent admixture.     

Impact of geographical isolation on genetic differentiation in insular and mainland populations of Weigela coraeensis (Caprifoliaceae) on Honshu and the Izu Islands

Aim To provide insights into genetic differentiation between insular endemic Weigela coraeensis var. fragrans and its progenitor variety W. coraeensis var. coraeensis, the population genetic structure of both varieties was examined, and factors promoting genetic differentiation between the two taxa were explored. Location The natural range of W. coraeensis (sensu lato) throughout mainland Japan (Honshu) and the Izu Islands. Methods The analysis included 349 and 504 individuals across the mainland (Honshu) and the Izu Islands, respectively, using 10 allozyme and 10 microsatellite loci. The population genetic structure of W. coraeensis was assessed by analysing genetic diversity indices for each population, genetic differentiation among populations, model‐based Bayesian clustering or distance‐based clustering, and bottleneck tests. Results The level of genetic diversity in each of the populations on the Izu Islands was negatively correlated with geographical distance between each island and the mainland. The populations on the mainland and on the Izu Islands were genetically differentiated to a certain extent; however, the microsatellite analyses suggested that gene flow also occurred between the mainland and the islands, and among individual islands. These microsatellite analyses also suggested recent bottlenecks in several populations in both areas. Main conclusions The decrease in genetic diversity throughout the Izu Islands, which correlated with distance to the mainland, Honshu, may be the result of a repeated founder effect occurring at a series of inter‐island colonizations from north to south. The stepping stone‐like configuration of the islands may have played a role in the dispersal of the species. Geographical isolation by sea would effectively result in genetic differentiation of W. coraeensis between mainland Honshu and the Izu Islands, although some gene flow may still occur between Honshu and the northern Izu Islands. The differentiation process of the endemic plants on the Izu Islands is anagenetic but not completed, and the study of these plants will provide insightful knowledge concerning the evolution of insular endemics.     

Does relaxed predation drive phenotypic divergence among insular populations?

The evolution of striking phenotypes on islands is a well‐known phenomenon, and there has been a long‐standing debate on the patterns of body size evolution on islands. The ecological causes driving divergence in insular populations are, however, poorly understood. Reduced predator fauna is expected to lower escape propensity, increase body size and relax selection for crypsis in small‐bodied, insular prey species. Here, we investigated whether escape behaviour, body size and dorsal coloration have diverged as predicted under predation release in spatially replicated islet and mainland populations of the lizard species Podarcis gaigeae. We show that islet lizards escape approaching observers at shorter distances and are larger than mainland lizards. Additionally, we found evidence for larger between‐population variation in body size among the islet populations than mainland populations. Moreover, islet populations are significantly more divergent in dorsal coloration and match their respective habitats poorer than mainland lizards. These results strongly suggest that predation release on islets has driven population divergence in phenotypic and behavioural traits and that selective release has affected both trait means and variances. Relaxed predation pressure is therefore likely to be one of the major ecological factors driving body size divergence on these islands.     

Rapid morpho‐functional changes among insular populations of the greater white‐toothed shrew

Islands are often considered to be natural laboratories where repeated ‘evolutionary experiments’ have taken place. Consequently, islands have been key model systems in our understanding of evolutionary theory. The greater white‐toothed shrew (Crocidura russula) is of interest as it has invaded French Atlantic islands within the last few thousand years and is considered to be morphologically and genetically stable in this area. In this article, we study the shape of the mandible of the greater white‐toothed shrew on four islands and compare it with that of individuals from populations on the mainland to quantify the effects of insularity. The degree of insularity (i.e. island size and distance to the continent) is thought to be linked to differences in ecological characteristics of islands compared with the mainland. We used geometric morphometric analyses to quantify differences in size and shape between populations and employed a simple biomechanical model to evaluate the potential effects of shape differences on bite force. Specimens from island populations are different from continental populations in shape and mechanical potential of the mandible. Among islands, the mandible shows various shapes that are correlated with both the distance from the coast and island area. The shape differences are located on different parts of the mandible, suggesting different ecological constraints on each island. Moreover, these shapes are linked to the ‘mechanical potential’, which is markedly different between islands. Mechanical potential has been suggested to evolve in response to prey size and or mechanical properties. In conclusion, our results show that, in spite of the relatively recent colonization of the Atlantic Islands, the mandible of C. russula possesses a distinct shape. Moreover, the shape differs among islands and is probably linked to the consumption of different prey. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Phenotypic diversification and island evolution of pipistrelle bats (Pipistrellus pipistrellus group) in the Mediterranean region inferred from geometric morphometrics and molecular phylogenetics

Aim The Mediterranean Basin is a centre of radiation for numerous species groups. To increase our understanding of the mechanisms underlying speciation and radiation events in this region, we assessed the phenotypic variability within the Pipistrellus pipistrellus–pygmaeus–hanaki species complex. Although bats form the second largest mammalian order, studies of insular evolution in this group are scarce. We approached this problem from a microevolutionary perspective and tested for the recurrence of the insular syndrome. Location The Mediterranean Basin, with a special focus on isolated populations from Corsica, the Maghreb, Cyprus, Cyrenaica and Crete. Methods Phenotypic variability was assessed by cranial morphometrics using the coordinates of 41 3D landmarks and associated geometric‐morphometric methods. We analysed 125 specimens representing all of the lineages in the species complex. Differences between taxa and between insular and continental populations in cranial size, shape, form and allometries were tested using analyses of variance and visualized using boxplots and canonical variate analysis. Relationships between molecular data from a previous study (cytochrome b sequences) and morphometric data were tested with co‐inertia analyses (RV test) and multivariate regressions. Results The three species were relatively well differentiated in cranial size and shape, and each species showed a significant amount of inter‐population variability. Comparisons of pairs of insular versus continental populations revealed heterogeneities in cranial patterns among island phenotypes, suggesting no recurrent insular syndrome. Molecular and phenotypic traits were correlated, except for molecular and lateral cranium shape. Main conclusions The Pipistrellus pipistrellus – pygmaeus – hanaki species complex exhibits phenotypic variability as a result of the fragmentation of its distribution (especially on islands), its phylogenetic and phylogeographic history and, most probably, other evolutionary factors that were not investigated in this study. We found no recurrent pattern of evolution on islands, indicating that site‐specific factors play a prevailing role on Mediterranean islands. The correlation between molecular and phenotypic data is incomplete, suggesting that factors other than phylogenetic relationships, potentially connected with feeding ecology, have played a role in shaping cranial morphology in this species complex.     

Genetic variation in island populations of tuatara (<Emphasis Type="Italic">Sphenodon</Emphasis> spp) inferred from microsatellite markers

Tuatara (Sphenodon spp) populations are restricted to 35 offshore islands in the Hauraki Gulf, Bay of Plenty and Cook Strait of New Zealand. Low levels of genetic variation have previously been revealed by allozyme and mtDNA analyses. In this new study, we show that six polymorphic microsatellite loci display high levels of genetic variation in 14 populations across the geographic range of tuatara. These populations are characterised by disjunct allele frequency spectra with high numbers of private alleles. High F _ST (0.26) values indicate marked population structure and assignment tests allocate 96% of all individuals to their source populations. These genetic data confirm that islands support genetically distinct populations. Principal component analysis and allelic sequence data supplied information about genetic relationships between populations. Low numbers of rare alleles and low allelic richness identified populations with reduced genetic diversity. Little Barrier Island has very low numbers of old tuatara which have retained some relictual diversity. North Brother Island’s tuatara population is inbred with fixed alleles at 5 of the 6 loci.     

Evidence of connectivity between continental and differentiated insular populations in a highly mobile species

Aim Genetically differentiated insular populations are candidates for independent units for conservation. However, occasional immigration to reduced island populations may occur and potentially have important consequences in their future viability and evolutionary potential. In this study, we investigate the conservation implications of population structure and connectivity of insular and continental populations of a migratory raptor as determined using genetic tools and satellite tracking. Location Western European populations in the Iberian Peninsula and two insular populations in the Mediterranean Sea (Balearic Islands) and Atlantic Ocean (Canary Islands). Methods We genotyped 22 microsatellite loci in 96 Egyptian vultures (Neophron percnopterus) from the Iberian Peninsula, 36 from Menorca (Balearic archipelago) and 242 (85% of the current population) from Fuerteventura (Canary Islands). We analysed genetic variation to estimate structure, gene flow, genetic diversity, effective size and recent demographic history of the populations. Additionally, 19 vultures were marked with satellite transmitters to track their migration routes. Results Insular populations were genetically differentiated from those of the mainland. We detected immigration in the insular populations and within the continental counterpart. We found similar levels of genetic variability between the continent and the islands, and a bottleneck analysis indicated recent sharp population declines in both archipelagos but not on the continent. Main conclusions Our study provides evidence that, in spite of significant differentiation, insular populations of highly mobile species may remain connected with the mainland. Conservation programmes should take into account population connectivity and integrate differentiated units of management within complex units of conservation that can best maintain processes and potential for evolutionary change.     

Mediterranean populations of the lesser white-toothed shrew (Crocidura suaveolens group): an unexpected puzzle of Pleistocene survivors and prehistoric introductions

An earlier study revealed the strong phylogeographical structure of the lesser white-toothed shrew (Crocidura suaveolens group) within the northern Palaearctic. Here, we aim to reconstruct the colonization history of Mediterranean islands and to clarify the biogeography and phylogeographical relationships of the poorly documented Middle East region with the northern Palaearctic. We performed analyses on 998-bp-long haplotypes of the mitochondrial cytochrome b gene of 143 samples collected around the Mediterranean basin, including islands and the Middle East. The analyses suggest that the Cypriot shrew belongs to the rare group of relict insular Pleistocene mammal taxa that have survived to the present day. In contrast, the Cretan, Corsican and Menorcan populations were independently introduced from the Middle East during the Holocene. The phylogeographical structure of this temperate Palaearctic species within the Middle East appears to be complex and rich in diversity, probably reflecting fragmentation of the area by numerous mountain chains. Four deeply divergent clades of the C. suaveolens group occur in the area, meaning that a hypothetical contact zone remains to be located in central western Iran.     

Microsatellites for tree of heaven (Ailanthus altissima)

Nine (CT)_n microsatellites were developed for tree of heaven, Ailanthus altissima, from invasive populations on the Mediterranean islands. These loci had seven to 12 alleles in 96 trees from five islands. Two loci had significant deficits of heterozygotes within islands while the other loci were in Hardy–Weinberg equilibrium, and four pairs of loci had significant linkage disequilibrium within a single island. These loci were also polymorphic in one to three individuals of the tree of heaven varieties, Ailanthus altissima erythrocarpa, Ailanthus altissima sutchuenensis and Ailanthus altissima tanakai, and the related species Ailanthus giraldii and Ailanthus vilmariniana.     

Population genetic structure of Sorex unguiculatus and Sorex caecutiens (Soricidae, Mammalia) in Hokkaido, based on microsatellite DNA polymorphism

We investigated the genetic structure of Sorex unguiculatus and Sorex caecutiens populations in Hokkaido, Japan, using hypervariable microsatellite DNA markers. We used five microsatellite loci to type 475 S. unguiculatus individuals from 20 localities on the Hokkaido mainland and four localities from each of four offshore islands (and 11 shrews from one locality in southern Sakhalin for a particular analysis). We used six microsatellite loci to type 240 S. caecutiens individuals from 13 localities on the Hokkaido mainland. Genetic variation was high in mainland populations of both species and low in the island populations of S. unguiculatus. Allelic richness and island size were positively correlated for S. unguiculatus, suggesting that genetic drift occurred on those islands due to small population size. In addition, four insular populations of S. unguiculatus were genetically differentiated from the mainland populations, although clear phylogeographic clustering was not confirmed among populations on the Hokkaido mainland for either S. unguiculatus or S. caecutiens. Heterozygosity excess was observed in more than half of the populations including the mainland populations of the two species, suggesting recent bottleneck events in these populations. Population dynamics of the shrews might be explained by a metapopulation scheme. According to autocorrelation analysis, the extent of non-random spatial genetic structure was approximately 100 km. Isolation by distance was observed in S. unguiculatus, but not in S. caecutiens although there is a positive trend. The lack of correlation for S. caecutiens might have been due to small sample size. Thus, no obvious differences in population genetic structure were found between the two species on the Hokkaido mainland in the present study, while previous investigations using mitochondrial DNA sequences inferred that these two species might have rather different biogeographic histories.     

Recent origin and adaptive diversification of <Emphasis Type="Italic">Ainsliaea</Emphasis> (Asteraceae) in the Ryukyu Islands: molecular phylogenetic inference using nuclear microsatellite markers

We investigated the phylogeny and phylogeography of four closely related Ainsliaea species (Asteraceae) on the continental Ryukyu Islands of eastern Asia, which consist of two flood-adapted “rheophyte” and two non-rheophyte (inland) species, based on 12 nuclear microsatellite loci. Phylogenetic analyses using 420 individuals from 26 populations showed that rheophytic A. linearis and A. oblonga are genetically distinct. Each species was clustered with the inland species that occur on the same islands, suggesting a different ancestry for the two rheophytes that evolved independently by local adaptation to flooded habitats. The results from the neighbor-joining clustering and principal coordinate analysis (PCoA) indicate that the southern populations of A. macroclinidioides are distinct lineages and ancestral to the northern populations as well as the other diverse species complex in the Ryukyus. These results suggest a pattern of colonization initially from the Asian mainland to the southern islands, followed by the northern islands via land bridges generated during the Quaternary glaciations. After isolation from southern populations, species radiation and regional differentiation within the northern clade occurred possibly via local adaptation and/or geographic isolation of the subdivided island bridge.     

Genetic distance between Nasutitermes takasagoensis (Isoptera: Termitidae) populations in Taiwan and the Yaeyama Islands, analyzed by amplified fragment length polymorphism markers

Dispersal ability and degree of inbreeding in a population can indirectly be assessed using genetic markers. It has been suggested that winged termites are not able to fly distances greater than several hundred meters. Using the amplified fragment length polymorphism (AFLP) technique, we previously analyzed the population substructure of Nasutitermes takasagoensis in the Yaeyama Islands, southern Japan. We found that there is moderate subpopulation structure based on the AFLP data. Moreover, the relatively low G_st and genetic distances among insular populations suggest that there is a possibility that winged termites are able to fly over distances of several kilometers. To learn more about this, in the present study, we compared new samples collected from the Hengchuen Peninsula in southern Taiwan with samples previously collected from the Yaeyama Islands. Using the samples collected in Taiwan, genetic distance was calculated against samples from six of the Yaeyama Islands. Genetic diversity, average heterozygosity, percentage of polymorphic loci, G_st and gene flow (Nm) were calculated. A total of 155 AFLP fragments were obtained for three primer combinations used, with 8 (5%) polymorphic bands. Genetic distance between the populations of Taiwan and the rest of the islands was greater than the genetic distance among the Yaeyama Islands. Although previous studies showed that average Nm among the Yaeyama Islands was 2.47, all of the observed Nm between Taiwan and the Yaeyama Islands were below 1. These findings suggest that the geographic distance between Taiwan and the Yaeyama Islands is large enough to prevent gene flow between them.     

Genetic and morphological variation in a partially isolated population of Caucasian shrew <Emphasis Type="Italic">Sorex satunini</Emphasis> (Mammalia)

Morphological and genetic variation at microsatellite loci of Caucasian shrew Sorex satunini Ogn. is examined and compared with that of the common shrew S. araneus L. Genetic distance at microsatellite loci between the common shrew and Caucasian shrew proved to be threefold higher than between chromosome races of the common shrew. The Caucasian shrew manifested low polymorphism in studies of both microsatellites and morphometric mandibular traits. The heterozygote deficit was also typical. These properties may be a consequence of partial isolation of the population and gene drift.     

Genomic islands of divergence linked to ecotypic variation in sockeye salmon

Regions of the genome displaying elevated differentiation (genomic islands of divergence) are thought to play an important role in local adaptation, especially in populations experiencing high gene flow. However, the characteristics of these islands as well as the functional significance of genes located within them remain largely unknown. Here, we used data from thousands of SNPs aligned to a linkage map to investigate genomic islands of divergence in three ecotypes of sockeye salmon (Oncorhynchus nerka) from a single drainage in southwestern Alaska. We found ten islands displaying high differentiation among ecotypes. Conversely, neutral structure observed throughout the rest of the genome was low and not partitioned by ecotype. One island on linkage group So13 was particularly large and contained six SNPs with F_ST > 0.14 (average F_ST of neutral SNPs = 0.01). Functional annotation revealed that the peak of this island contained a nonsynonymous mutation in a gene involved in growth in other species (TULP4). The islands that we discovered were relatively small (80–402 Kb), loci found in islands did not show reduced levels of diversity, and loci in islands displayed slightly elevated linkage disequilibrium. These attributes suggest that the islands discovered here were likely generated by divergence hitchhiking; however, we cannot rule out the possibility that other mechanisms may have produced them. Our results suggest that islands of divergence serve an important role in local adaptation with gene flow and represent a significant advance towards understanding the genetic basis of ecotypic differentiation.