Associations with habitat versus geographic cohesiveness: size and shape of Bembicium vittatum Philippi (Gastropoda: Littorinidae) in the Houtman Abrolhos Islands

In the Houtman Abrolhos Islands, Western Australia, the direct-developing littorine snail Bembicium vittatum occupies a wide range of habitats, which are replicated across the three major groups of islands. Earlier studies showed that allozyme similarities followed patterns related to gene flow, independent of habitat, providing an excellent opportunity to test for associations with habitat for traits more likely to be adaptively important. As the first test for adaptive divergence, we examined variation in size and shape of shells among 131 populations in the Abrolhos Islands. Two-fold variations were found in width of adults, the allometric coefficient of height with width, and shell height scaled to a standard width. Quantification of habitat characteristics was summarized by principal components analysis. In contrast with the patterns of divergence for allozymes, shell height, adjusted for width, was strongly associated with habitat: flatter shells are found on exposed, vertical shores, while domed, more globose shells predominate in sheltered sites. This association was stronger for shape of adult-sized snails than for height scaled to an arbitrary size, highlighting the importance of using biologically relevant measures. Even highly isolated and allozymically less variable populations in tidal ponds conformed to this association. Because differences in shape are highly heritable in B. vittatum , this association of shape with habitat, independent of patterns of gene flow, indicates local adaptation. Shell size also varied with habitat, but because growth rate is highly plastic, variation in size cannot be interpreted simply in terms of adaptation. Nevertheless, the pattern of variation indicates that, within realized limits, larger size is generally favourable, but may be constrained by local conditions. Thus, variation in size signals the potential for adaptive divergence of life histories among the many, isolated populations of this species.     

Adaptive responses of independent traits to the same environmental gradient in the intertidal snail Bembicium vittatum

The snail Bembicium vittatum occupies a wide range of intertidal habitats in the Houtman Abrolhos Islands, Western Australia. Allozyme variation reflects patterns of connectivity, which are independent of local habitat. In contrast, heritable differences in shell shape among 83 shore sites vary with habitat, indicating local adaptation. Here we examine dimorphisms of colour and spotting of the shell in the same populations, as a test of consistency and complexity of patterns of local adaptation. Within populations, the frequency of spotted shells is higher in dark shells. Despite this association, spatial variations of colour and spotting are only weakly correlated. As predicted for traits associated with local adaptation, subdivision is greater for colour, spotting and shape than for allozymes. Colour and shape are associated with local habitat, such that populations on vertical shores have higher frequencies of dark and relatively flatter shells than those on gently sloping shores. These associations are repeatable between three separate groups of islands. Spotting shows a weaker, but significant association with the same gradient. Although shape does not differ between colour morphs within populations, the proportion of dark shells is strongly associated with shape. Thus, the independent shell traits are apparently adapted to a common, biologically significant gradient, even though the adaptive mechanisms probably differ for colour and shape. The parallel variations of independent traits highlight both the complexity of local adaptation and the potential to reveal evolutionarily significant environmental contrasts by examining adaptively relevant traits.     

Genetic divergence of peripherally disjunct populations of the gastropod Batillariella estuarina in the Houtman Abrolhos Islands, Western Australia

Geographically disjunct populations are unusual in marine species, but the Houtman Abrolhos Islands, Western Australia, provide opportunities to study highly disjunct peripheral isolates of several species. The intertidal snail Batillariella estuarina occurs in isolated tidal ponds in the Abrolhos Islands, where it is at its northern limit, disjunct from mainland populations by 600-900 km. The species is thus disjunct both geographically and among the peripherally isolated populations in the Abrolhos Islands. Comparisons of allozymes at 11 polymorphic loci were made among populations from 10 ponds in the Abrolhos Islands and six sites from relatively continuous tidal flats at Albany, 900 km away, the nearest major set of populations. Among all 16 populations, subdivision was high (FST = 0.455). Although there were subtle differences between the geographical regions, the large majority of divergence occurred among the isolated ponds in the Abrolhos (FST = 0.441), and divergence on the tidal flats at Albany was only moderate (FST = 0.085). Characteristic of peripheral isolates, the pond populations have less polymorphism and fewer alleles than the more connected populations at Albany. Combined with evidence of genetic divergence in the gastropods Bembicium vittatum and Austrocochlea constricta, which have very similar geographical distributions to that of B. estuarina, these results indicate the potential evolutionary significance of peripherally isolated marine populations in the unusual habitats of the Abrolhos Islands.     

Genetic differentiation and gene flow among populations of the alpine butterfly, Parnassius smintheus, vary with landscape connectivity

Levels of gene flow among populations vary both inter- and intraspecifically, and understanding the ecological bases of variation in levels of gene flow represents an important link between the ecological and evolutionary dynamics of populations. The effects of habitat spatial structure on gene flow have received considerable attention; however, most studies have been conducted at a single spatial scale and without background data on how individual movement is affected by landscape features. We examined the influence of habitat connectivity on inferred levels of gene flow in a high-altitude, meadow-dwelling butterfly, Parnassius smintheus. For this species, we had background data on the effects of landscape structure on both individual movement and on small-scale population genetic differentiation. We compared genetic differentiation and patterns of isolation by distance, based on variation at seven microsatellite loci, among three regions representing two levels of connectivity of high-altitude, nonforested habitats. We found that reduced connectivity of habitats, resulting from more forest cover at high altitudes, was associated with greater genetic differentiation among populations (higher estimated FST), a breakdown of isolation by distance, and overall lower levels of inferred gene flow. These observed differences were consistent with expectations based on our knowledge of the movement behaviour of this species and on previous population genetic analyses conducted at the smaller spatial scale. Our results indicate that the role of gene flow may vary among groups of populations depending on the interplay between individual movement and the structure of the surrounding landscape.     

Isolation by resistance across a complex coral reef seascape

A detailed understanding of the genetic structure of populations and an accurate interpretation of processes driving contemporary patterns of gene flow are fundamental to successful spatial conservation management. The field of seascape genetics seeks to incorporate environmental variables and processes into analyses of population genetic data to improve our understanding of forces driving genetic divergence in the marine environment. Information about barriers to gene flow (such as ocean currents) is used to define a resistance surface to predict the spatial genetic structure of populations and explain deviations from the widely applied isolation-by-distance model. The majority of seascape approaches to date have been applied to linear coastal systems or at large spatial scales (more than 250 km), with very few applied to complex systems at regional spatial scales (less than 100 km). Here, we apply a seascape genetics approach to a peripheral population of the broadcast-spawning coral Acropora spicifera across the Houtman Abrolhos Islands, a high-latitude complex coral reef system off the central coast of Western Australia. We coupled population genetic data from a panel of microsatellite DNA markers with a biophysical dispersal model to test whether oceanographic processes could explain patterns of genetic divergence. We identified significant variation in allele frequencies over distances of less than 10 km, with significant differentiation occurring between adjacent sites but not between the most geographically distant ones. Recruitment probabilities between sites based on simulated larval dispersal were projected into a measure of resistance to connectivity that was significantly correlated with patterns of genetic divergence, demonstrating that patterns of spatial genetic structure are a function of restrictions to gene flow imposed by oceanographic currents. This study advances our understanding of the role of larval dispersal on the fine-scale genetic structure of coral populations across a complex island system and applies a methodological framework that can be tailored to suit a variety of marine organisms with a range of life-history characteristics.     

Fine‐grained adaptive divergence in an amphibian: genetic basis of phenotypic divergence and the role of nonrandom gene flow in restricting effective migration among wetlands

Adaptive ecological differentiation among sympatric populations is promoted by environmental heterogeneity, strong local selection and restricted gene flow. High gene flow, on the other hand, is expected to homogenize genetic variation among populations and therefore prevent local adaptation. Understanding how local adaptation can persist at the spatial scale at which gene flow occurs has remained an elusive goal, especially for wild vertebrate populations. Here, we explore the roles of natural selection and nonrandom gene flow (isolation by breeding time and habitat choice) in restricting effective migration among local populations and promoting generalized genetic barriers to neutral gene flow. We examined these processes in a network of 17 breeding ponds of the moor frog Rana arvalis, by combining environmental field data, a common garden experiment and data on variation in neutral microsatellite loci and in a thyroid hormone receptor (TRβ) gene putatively under selection. We illustrate the connection between genotype, phenotype and habitat variation and demonstrate that the strong differences in larval life history traits observed in the common garden experiment can result from adaptation to local pond characteristics. Remarkably, we found that haplotype variation in the TRβ gene contributes to variation in larval development time and growth rate, indicating that polymorphism in the TRβ gene is linked with the phenotypic variation among the environments. Genetic distance in neutral markers was correlated with differences in breeding time and environmental differences among the ponds, but not with geographical distance. These results demonstrate that while our study area did not exceed the scale of gene flow, ecological barriers constrained gene flow among contrasting habitats. Our results highlight the roles of strong selection and nonrandom gene flow created by phenological variation and, possibly, habitat preferences, which together maintain genetic and phenotypic divergence at a fine‐grained spatial scale.     

Comparative phylogeography of tenebrionid beetles in the Aegean archipelago: the effect of dispersal ability and habitat preference

Comparative phylogeographical studies in island archipelagos can reveal lineage-specific differential responses to the geological and climatic history. We analysed patterns of genetic diversity in six codistributed lineages of darkling beetles (Tenebrionidae) in the central Aegean archipelago which differ in wing development and habitat preferences. A total of 600 specimens from 30 islands and eight adjacent mainland regions were sequenced for mitochondrial cytochrome oxidase I and nuclear Muscular protein 20. Individual gene genealogies were assessed for the presence of groups that obey an independent coalescent process using a mixed Yule coalescent model. The six focal taxa differed greatly in the number of coalescent groups and depth of lineage subdivision, which was closely mirrored by the degree of geographical structuring. The most severe subdivision at both mitochondrial DNA and nuclear DNA level was found in flightless lineages associated with presumed stable compact-soil habitats (phrygana, maquis), in contrast to sand-obligate lineages inhabiting ephemeral coastal areas that displayed greater homogeneity across the archipelago. A winged lineage, although associated with stable habitats, showed no significant phylogenetic or geographical structuring. Patterns of nucleotide diversity and local genetic differentiation, as measured using Φ_ST and hierarchical amova , were consistent with high levels of ongoing gene flow in the winged taxon; frequent local extinction and island recolonisation for flightless sand-obligate taxa; and very low gene flow and geographical structure largely defined by the palaeogeographical history of the region in flightless compact-soil taxa. These results show that differences in dispersal rate, mediated by habitat persistence, greatly influence the levels of phylogeographical subdivision in lineages that are otherwise subjected to the same geological events and palaeoclimatic changes.     

Islands increase genetic subdivision and disrupt patterns of connectivity of intertidal snails in a complex archipelago

The view that marine species with planktonic dispersal have highly connected, demographically open populations is giving way to recognition that populations may often be largely self-recruiting, or demographically closed. This raises the question of what local conditions might favor isolation of populations. To test the importance of islands for local isolation in species with planktonic larvae, we examined allozyme variation among 35 populations of the intertidal snail Austrocochlea constricta in the Houtman Abrolhos Islands, Western Australia, spanning 60 km. Heterogeneity of allozyme frequencies among populations was high, with average F(ST) of 0.237, indicating highly localized populations. Increased subdivision was associated with islands at different scales: between island groups, separated by deep water gaps, and between disconnected sets of islands within groups. At short distances, up to two km, subdivision increased fivefold between islands compared with that between populations on the same island. Along 11 km of continuous, sheltered shore, there was isolation by distance but among a linear series of islands over similar distance, there was greater subdivision at short distances but no association with distance. These patterns had been seen previously in the direct-developing snail Bembicium vittatum, but its finding in A. constricta confirms for a planktonic disperser the importance of this complex archipelago for both retention of locally produced larvae and disruption of patterns of connectivity. Taken together, these results indicate that islands can increase both the "open" and the "closed" components of recruitment and that applicable models of genetic connectivity depend substantially on local conditions.     

Hierarchical analysis of genetic structure in the habitat‐specialist Eastern Sand Darter (Ammocrypta pellucida)

Quantifying spatial genetic structure can reveal the relative influences of contemporary and historic factors underlying localized and regional patterns of genetic diversity and gene flow – important considerations for the development of effective conservation efforts. Using 10 polymorphic microsatellite loci, we characterize genetic variation among populations across the range of the Eastern Sand Darter (Ammocrypta pellucida), a small riverine percid that is highly dependent on sandy substrate microhabitats. We tested for fine scale, regional, and historic patterns of genetic structure. As expected, significant differentiation was detected among rivers within drainages and among drainages. At finer scales, an unexpected lack of within‐river genetic structure among fragmented sandy microhabitats suggests that stratified dispersal resulting from unstable sand bar habitat degradation (natural and anthropogenic) may preclude substantial genetic differentiation within rivers. Among‐drainage genetic structure indicates that postglacial (14 kya) drainage connectivity continues to influence contemporary genetic structure among Eastern Sand Darter populations in southern Ontario. These results provide an unexpected contrast to other benthic riverine fish in the Great Lakes drainage and suggest that habitat‐specific fishes, such as the Eastern Sand Darter, can evolve dispersal strategies that overcome fragmented and temporally unstable habitats.     

Contrasting demographic and genetic estimates of dispersal in the endangered Coahuilan box turtle: a contemporary approach to conservation

The evolutionary viability of an endangered species depends upon gene flow among subpopulations and the degree of habitat patch connectivity. Contrasting population connectivity over ecological and evolutionary timescales may provide novel insight into what maintains genetic diversity within threatened species. We employed this integrative approach to evaluating dispersal in the critically endangered Coahuilan box turtle (Terrapene coahuila) that inhabits isolated wetlands in the desert‐spring ecosystem of Cuatro Ciénegas, Mexico. Recent wetland habitat loss has altered the spatial distribution and connectivity of habitat patches; and we therefore predicted that T. coahuila would exhibit limited movement relative to estimates of historic gene flow. To evaluate contemporary dispersal patterns, we employed mark–recapture techniques at both local (wetland complex) and regional (intercomplex) spatial scales. Gene flow estimates were obtained by surveying genetic variation at nine microsatellite loci in seven subpopulations located across the species’ geographical range. The mark–recapture results at the local spatial scale reveal frequent movement among wetlands that was unaffected by interwetland distance. At the regional spatial scale, dispersal events were relatively less frequent between wetland complexes. The complementary analysis of population genetic substructure indicates strong historic gene flow (global F_ST = 0.01). However, a relationship of genetic isolation by distance across the geographical range suggests that dispersal limitation exists at the regional scale. Our approach of contrasting direct and indirect estimates of dispersal at multiple spatial scales in T. coahuila conveys a sustainable evolutionary trajectory of the species pending preservation of threatened wetland habitats and a range‐wide network of corridors.     

AFLPs and Mitochondrial Haplotypes Reveal Local Adaptation to Extreme Thermal Environments in a Freshwater Gastropod

The way environmental variation shapes neutral and adaptive genetic variation in natural populations is a key issue in evolutionary biology. Genome scans allow the identification of the genetic basis of local adaptation without previous knowledge of genetic variation or traits under selection. Candidate loci for divergent adaptation are expected to show higher F_ST than neutral loci influenced solely by random genetic drift, migration and mutation. The comparison of spatial patterns of neutral markers and loci under selection may help disentangle the effects of gene flow, genetic drift and selection among populations living in contrasting environments. Using the gastropod Radix balthica as a system, we analyzed 376 AFLP markers and 25 mtDNA COI haplotypes for candidate loci and associations with local adaptation among contrasting thermal environments in Lake Mývatn, a volcanic lake in northern Iceland. We found that 2% of the analysed AFLP markers were under directional selection and 12% of the mitochondrial haplotypes correlated with differing thermal habitats. The genetic networks were concordant for AFLP markers and mitochondrial haplotypes, depicting distinct topologies at neutral and candidate loci. Neutral topologies were characterized by intense gene flow revealed by dense nets with edges connecting contrasting thermal habitats, whereas the connections at candidate loci were mostly restricted to populations within each thermal habitat and the number of edges decreased with temperature. Our results suggest microgeographic adaptation within Lake Mývatn and highlight the utility of genome scans in detecting adaptive divergence.     

Population subdivision in westslope cutthroat trout (Oncorhynchus clarki lewisi) at the northern periphery of its range: evolutionary inferences and conservation implications

Westslope cutthroat trout (Oncorhynchus clarki lewisi, Salmonidae) are native to the upper Columbia, Missouri, and South Saskatchewan river drainages of western North America and are at the northern periphery of their range in southeastern British Columbia, Canada. We examined geographical variation in allele frequencies at eight microsatellite loci in 36 samples of westslope cutthroat trout from British Columbia to assess levels of population subdivision and to test the hypothesis that different habitat types (principally mainstem vs. above migration barrier habitats) would influence levels of genetic diversity, genetic divergence among populations, and attainment of equilibrium between gene flow and genetic drift. Across all samples, the mean number of alleles per locus was 3.9 and mean expected heterozygosity was 0.56. Population subdivision was extensive with an overall Fst (theta) of 0.32. Populations sampled above migration barriers had significantly fewer alleles, lower expected heterozygosity, but greater average pairwise Fst than populations sampled from mainstem localities. We found evidence for isolation-by-distance from a significant correlation between genetic distance and geographical distance (r = 0.31), but the pattern was much stronger (r = 0.51) when above barrier populations and a population that may have been involved in headwater exchanges were removed. By contrast, isolation-by-distance was not observed when only above barrier populations were tested among themselves. Our data support the maintenance of separate demographic management strategies for westslope cutthroat trout inhabiting different river systems and illustrate how differing habitat structure (e.g. presence of migration barriers) may influence patterns of biodiversity and gene flow-drift equilibrium.     

Population structure and landscape genetics in the endangered subterranean rodent Ctenomys porteousi

In order to devise adequate conservation and management strategies for endangered species, it is important to incorporate a reliable understanding of its spatial population structure, detecting the existence of demographic partitions throughout its geographical range and characterizing the distribution of its genetic diversity. Moreover, in species that occupy fragmented habitats it is essential to know how landscape characteristics may affect the genetic connectivity among populations. In this study we use eight microsatellite markers to analyze population structure and gene flow patterns in the complete geographic range of the endangered rodent Ctenomys porteousi. Also, we use landscape genetics approaches to evaluate the effects of landscape configuration on the genetic connectivity among populations. In spite of geographical proximity of the sampling sites (8–27 km between the nearest sites) and the absence of marked barriers to individual movement, strong population structure and low values of gene flow were observed. Genetic differentiation among sampling sites was consistent with a simple model of isolation by distance, where peripheral areas showed higher population differentiation than those sites located in the central area of the species’ distribution. Landscape genetics analysis suggested that habitat fragmentation at regional level has affected the distribution of genetic variation among populations. The distance of sampling sites to areas of the landscape having higher habitat connectivity was the environmental factor most strongly related to population genetic structure. In general, our results indicate strong genetic structure in C. porteousi, even at a small spatial scale, and suggest that habitat fragmentation could increase the population differentiation.     

Influence of volcanic activity on the population genetic structure of Hawaiian Tetragnatha spiders: fragmentation, rapid population growth and the potential for accelerated evolution

Volcanic activity on the island of Hawaii results in a cyclical pattern of habitat destruction and fragmentation by lava, followed by habitat regeneration on newly formed substrates. While this pattern has been hypothesized to promote the diversification of Hawaiian lineages, there have been few attempts to link geological processes to measurable changes in population structure. We investigated the genetic structure of three species of Hawaiian spiders in forests fragmented by a 150-year-old lava flow on Mauna Loa Volcano, island of Hawaii: Tetragnatha quasimodo (forest and lava flow generalist), T. anuenue and T. brevignatha (forest specialists). To estimate fragmentation effects on population subdivision in each species, we examined variation in mitochondrial and nuclear genomes (DNA sequences and allozymes, respectively). Population subdivision was higher for forest specialists than for the generalist in fragments separated by lava. Patterns of mtDNA sequence evolution also revealed that forest specialists have undergone rapid expansion, while the generalist has experienced more gradual population growth. Results confirm that patterns of neutral genetic variation reflect patterns of volcanic activity in some Tetragnatha species. Our study further suggests that population subdivision and expansion can occur across small spatial and temporal scales, which may facilitate the rapid spread of new character states, leading to speciation as hypothesized by H. L. Carson 30 years ago.     

A comparative study on genetic effects of artificial and natural habitat fragmentation on Loropetalum chinense (Hamamelidaceae) in Southeast China

Elucidating the demographic and landscape features that determine the genetic effects of habitat fragmentation has become fundamental to research in conservation and evolutionary biology. Land-bridge islands provide ideal study areas for investigating the genetic effects of habitat fragmentation at different temporal and spatial scales. In this context, we compared patterns of nuclear microsatellite variation between insular populations of a shrub of evergreen broad-leaved forest, Loropetalum chinense, from the artificially created Thousand-Island Lake (TIL) and the Holocene-dated Zhoushan Archipelago of Southeast China. Populations from the TIL region harboured higher levels of genetic diversity than those from the Zhoushan Archipelago, but these differences were not significant. There was no correlation between genetic diversity and most island features, excepting a negative effect of mainland–island distance on allelic richness and expected heterozygosity in the Zhoushan Archipelago. In general, levels of gene flow among island populations were moderate to high, and tests of alternative models of population history strongly favoured a gene flow-drift model over a pure drift model in each region. In sum, our results showed no obvious genetic effects of habitat fragmentation due to recent (artificial) or past (natural) island formation. Rather, they highlight the importance of gene flow (most likely via seed) in maintaining genetic variation and preventing inter-population differentiation in the face of habitat ‘insularization'' at different temporal and spatial scales.     

Phenotypic divergence despite high levels of gene flow in Galápagos lava lizards (Microlophus albemarlensis)

The extent of evolutionary divergence of phenotypes between habitats is predominantly the result of the balance of differential natural selection and gene flow. Lava lizards (Microlophus albemarlensis) on the small island of Plaza Sur in the Galápagos archipelago inhabit contrasting habitats: dense vegetation on the western end of the island thins rapidly in a transitional area, before becoming absent on the eastern half. Associated with these habitats are phenotypic differences in traits linked to predator avoidance (increased wariness, sprint speed, and endurance in lizards from the sparsely vegetated habitat). This population provides an opportunity to test the hypothesis that reduced gene flow is necessary for phenotypic differentiation. There was no evidence of any differences among habitats in allele frequencies at six out of seven microsatellite loci examined, nor was there any indication of congruence between patterns of genetic variability and the change in vegetation regime. We infer that gene flow between the habitats on Plaza Sur must be sufficiently high to overcome genetic drift within habitats but that it does not preclude phenotypic differentiation.     

Genetic variation and population differentiation in the lichen-forming ascomycete Xanthoria parietina on the island Storfosna, central Norway

Genetic diversity and fine-scale population structure in the lichen-forming ascomycete Xanthoria parietina was investigated using sequence variation in part of the intergenic spacer (IGS) and the complete internal transcribed spacer (ITS) regions of the nuclear ribosomal DNA. Sampling included 213 and 225 individuals, respectively, from seven populations in two different habitats, bark and rock, on the island Storfosna off the central west coast of Norway. Both markers revealed significant variation and a total of 10 IGS and 16 ITS haplotypes were found. There were no signs of significant positive spatial autocorrelation at any spatial size class down to 10% of transect length, nor did we find significant deviations from neutrality or signs of historical population expansion. Analysis of molecular variance (amova) indicated that most of the genetic variance observed was within populations, but when populations were grouped according to habitat, more than a quarter of the variance was explained among groups. Pairwise comparisons of populations (F(ST), exact tests of population differentiation) revealed significant differentiation between populations in different habitats (on bark or rock), but not between populations in the same habitat. Haplotype networks show that internal and presumably old haplotypes are shared between habitats, whereas terminal haplotypes tend to be unique to a habitat, mostly bark. We interpret the observed pattern to mean that there is no evidence of restricted gene flow between populations in the same habitat at the present spatial scale (interpopulation distances one or a few kilometres). On the other hand, differentiation between habitats is considerable, which we attribute to restricted gene flow between habitats (habitat isolation). Evidence suggests that the observed differentiation did not evolve locally. Estimates of divergence time between populations in the respective habitats indicate that an ancestral population started to diverge at least 34,000 years ago but probably much further back in time.     

Spatial genetic structure in a metapopulation of the land snail Cepaea nemoralis (Gastropoda: Helicidae)

Habitat fragmentation is a major force affecting demography and genetic structure of wild populations, especially in agricultural landscapes. The land snail Cepaea nemoralis (L.) was selected to investigate the impact of habitat fragmentation on the spatial genetic structure of an organism with limited dispersal ability. Genetic and morphological patterns were investigated at a local scale of a 500 m transect and a mesoscale of 4 x 4 km in a fragmented agricultural landscape while accounting for variation in the landscape using least-cost models. Analysis of microsatellite loci using expected heterozygosity (HE), pairwise genetic distance (FST/1-FST) and spatial autocorrelograms (Moran's I) as well as shell characteristics revealed spatial structuring at both scales and provided evidence for a metapopulation structure. Genetic diversity was related to morphological diversity regardless of landscape properties. This pointed to bottlenecks caused by founder effects after (re)colonization. Our study suggests that metapopulation structure depended on both landscape features and the shape of the dispersal function. A range of genetic spatial autocorrelation up to 80 m at the local scale and up to 800 m at the mesoscale indicated leptokurtic dispersal patterns. The metapopulation dynamics of C. nemoralis resulted in a patchwork of interconnected, spatially structured subpopulations. They were shaped by gene flow which was affected by landscape features, the dispersal function and an increasing role of genetic drift with distance.     

Hierarchical analysis of population genetic structure in the monogynous ant Cataglyphis cursor using microsatellite and mitochondrial DNA markers

Despite having winged queens, female dispersal in the monogynous ant Cataglyphis cursor is likely to be restricted because colonies reproduce by fission. We investigated the pattern of population genetic structure of this species using eight microsatellite markers and a mitochondrial DNA (mtDNA) sequence, in order to examine the extent of female and nuclear gene flow in two types of habitat. Sampling was carried out at a large spatial scale (16 sites from 2.5 to 120 km apart) as well as at a fine spatial scale (two 4.5-km transects, one in each habitat type). The strong spatial clustering of mtDNA observed at the fine spatial scale strongly supported a restricted effective female dispersal. In agreement, patterns of the mtDNA haplotypes observed at large and fine spatial scales suggested that new sites are colonized by nearby sites. Isolation by distance and significant nuclear genetic structure have been detected at all the spatial scales investigated. The level of local genetic differentiation for mitochondrial marker was 15 times higher than for the nuclear markers, suggesting differences in dispersal pattern between the two sexes. However, male gene flow was not sufficient to prevent significant nuclear genetic differentiation even at short distances (500 m). Isolation-by-distance patterns differed between the two habitat types, with a linear decrease of genetic similarities with distance observed only in the more continuous of the two habitats. Finally, despite these low dispersal capacities and the potential use of parthenogenesis to produce new queens, no signs of reduction of nuclear genetic diversity was detected in C. cursor populations.