Combining demography and genetic analysis to assess the population structure of an amphibian in a human-dominated landscape

In this article, we applied demographic and genetic approaches to assess how landscape features influence dispersal patterns and genetic structure of the common frog Rana temporaria in a landscape where anthropogenic perturbations are pervasive (urbanization and roads). We used a combination of GIS methods that integrate radiotracking and landscape configuration data, and simulation techniques in order to estimate the potential dispersal area around breeding patches. Additionally, genetic data provided indirect measures of dispersal and allowed to characterise the spatial genetic structure of ponds and the patterns of gene flow across the landscape. Although demographic simulations predicted six distinct groups of habitat patches within which movement can occur, genetic analyses suggested a different configuration. More precisely, BAPS5 spatial clustering method with ponds as the analysis unit detected five spatial clusters. Individual-based analyses were not able to detect significant genetic structure. We argue that (1) taking into account that each individual breeds in specific breeding patch allowed for better explanation of population functioning, (2) the discrepancy between direct (radiotracking) and indirect (genetic) estimates of subpopulations (breeding patches) is due to a recent landscape fragmentation (e.g. traffic increase). We discuss the future of this population in the face of increasing landscape fragmentation, focusing on the need for combining demographic and genetic approaches when evaluating the conservation status of population subjected to rapid landscape changes.     

Where movement happens: scale‐dependent landscape effects on genetic differentiation in the European tree frog

Functional connectivity among fragmented populations depends on the landscape matrix between occupied habitat patches and its effect on the frequency of animal movement and gene flow. The quantification of landscape effects on gene flow should therefore be scale‐dependent. Here, we explored the impact of different spatial scales in a landscape genetic analysis of the European tree frog Hyla arborea in a fragmented landscape in Switzerland. We examined the effects of landscape elements and geographic distance on genetic differentiation at three distance classes reflecting varying frequencies of tree frog movement. We calculated pairwise F_ST‐values and assembled 16 landscape elements within 1 km wide corridors between all pairs of tree frog breeding sites. Per distance class, we computed a multiple regression model with stepwise backward elimination and permutation testing. At distances of<2 km, only a larger river acted as a barrier to gene flow. At distances>2 km, geographic distance had a negative effect on gene flow as had landscape elements such as forests and roads. In general, hedgerows and various structure‐rich landscape elements positively affected gene flow. As we found distinct scale‐dependent landscape effects on gene flow, future landscape genetic studies should analyse the effects of landscape variables at different spatial dimensions relevant for the movement and dispersal of the study organisms. Corresponding studies should also carefully consider relevant correlations among the landscape elements tested and should preferentially replicate their analysis at the landscape‐level in order to avoid idiosyncratic results owing to the particular scale and landscape studied.     

The effects of habitat fragmentation via forestry plantation establishment on spatial genotypic structure in the small marsupial carnivore, Antechinus agilis

Dispersal is an important influence on species' distributions, patch colonization and population persistence in fragmented habitat. We studied the impacts of habitat fragmentation resulting from establishment of an exotic pine plantation on dispersal of the marsupial carnivore, Antechinus agilis. We applied spatial analyses of individual multilocus microsatellite genotypes and mitochondrial haplotypes to study patterns of gene flow in fragmented habitat and natural habitat 'control' areas, and how this is affected by the spatial dispersion of habitat patches, the presence of corridors and a 'mainland' source of migrants. Spatial analysis of molecular variance and partial Mantel tests confirmed the absence of cryptic barriers to gene flow in continuous habitat, which if present would confound the comparison of genetic structures in fragmented vs. unfragmented habitats. Spatial genotypic structure suggested that although dispersal was male-biased in both habitat types, fragmentation restricted dispersal of males more than that of females and the degree of restriction of male dispersal was dependent on the geographical isolation of the patch. The scale of positive genotypic structure in fragmented habitat was restricted to the two closest patches for females and the three closest patches for males. Our results provide evidence for significantly increased gene flow through habitat corridors relative to that across the matrix and for significantly lower gene flow between 'mainland' unfragmented habitat and habitat patches relative to that within either habitat type, suggesting a behavioural barrier to crossing habitat interfaces.     

The role of pollutant accumulation in determining the use of stormwater ponds by amphibians

Urbanization often results in the creation of habitats such as stormwater management ponds. Although stormwater ponds are designed to retain runoff and associated pollutants, they are frequently colonized by wildlife including pond-breeding amphibians. Understanding of the ecological function of these created habitats is limited. This study investigated the role of pollutants in shaping use of stormwater ponds by amphibians. A survey of 68 stormwater ponds in Baltimore County, Maryland, and statistical modeling found wood frogs (Rana [= Lithobates] sylvatica) were more likely to breed in ponds with longer hydroperiods and Cl^? concentrations below approximately 250 mg/L. American toad (Bufo [= Anaxyrus] americanus) use of ponds was primarily influenced by hydroperiod; toads were more likely to use longer hydroperiod ponds. To confirm use was a result of toxicity and differential sensitivity among species, wood frog and American toad embryos and larvae were exposed to sediment from six stormwater ponds spanning the range of pollutant conditions documented in the field. Survival of wood frogs through metamorphosis was related to metal and salt levels of pond sediments, but survival of American toads was not. In agreement with the field study, no wood frog larvae survived to metamorphosis when Cl^? levels were above 260 mg/L. The results suggest that pollutants that accumulate in stormwater ponds, specifically road deicing salts, are acting as local filters capable of creating unique assemblages of anuran larvae in urban areas.     

Structure and fragmentation of growling grass frog metapopulations

Metapopulations occur in fragmented landscapes, and consist of demographically-independent populations connected by dispersal. Nevertheless, anthropogenic habitat fragmentation may be fatal to metapopulations, as it disrupts dispersal and gene flow, and undermines the balance between population extinction and colonization. Understanding the extent to which particular land-use practices disrupt dispersal and gene flow is therefore crucial for conserving metapopulations. We examined the structure and fragmentation of metapopulations of the endangered growling grass frog (Litoria raniformis) in an urbanizing landscape in southern Australia. Population clustering analyses revealed three distinct genetic units, corresponding to the three wetland clusters sampled. Isolation-by-distance was apparent between populations, and genetic distance was significantly correlated with the presence of urban barriers between populations. Our study provides evidence that urbanization fragments metapopulations of L. raniformis. Managers of L. raniformis in urbanizing landscapes should seek to mitigate effects of urbanization on dispersal and gene flow.     

Limited influence of local and landscape factors on finescale gene flow in two pond‐breeding amphibians

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis between the ponds. We found overall high genetic connectivity across distances up to 17 km for both species and a limited effect of natural and anthropogenic factors on gene flow. We found the null models best explained patterns of genetic differentiation at a local level and found several factors at the landscape level that weakly influenced gene flow. This research indicates multiscale investigations that incorporate local and landscape factors are valuable for understanding patterns of gene flow. Our findings suggest that dispersal rates in this system are high enough to minimize genetic structuring and that current forestry practices do not significantly impede dispersal.     

Microsatellite variation and population structure of a recovering Tree frog (Hyla arborea L.) metapopulation

Numbers and sizes of populations of the European tree frog in The Netherlands have dramatically decreased in the second half of the last century due to extensive habitat destruction and fragmentation. We have studied the genetic structure of a slowly recovering meta-population. Strong genetic differentiation, estimated at eight microsatellite loci, was found between clusters of populations (F _st-values above 0.2). Within clusters, consisting of ponds within a radius of about 5 km, European tree frog populations were less differentiated (F _st<0.08) and exact tests showed that most of the ponds within clusters were not significantly differentiated. Although local population sizes have been increasing since 1989, and some new ponds have been colonised in the direct vicinity of ponds that have been populated continuously, little evidence for gene flow between clusters of ponds was found (only one exception). Furthermore, levels of genetic diversity were low compared to populations in comparable areas elsewhere in Europe. Therefore, a continuous conservation effort is needed to prevent any further loss of genetic diversity. The alleviation of important barriers to dispersal between the clusters should be given a high priority for the restoration of the meta-population as a whole.     

Fragmentation of Atlantic Forest has not affected gene flow of a widespread seed‐dispersing bat

Habitat loss and resultant fragmentation are major threats to biodiversity, particularly in tropical and subtropical ecosystems. It is increasingly urgent to understand fragmentation effects, which are often complex and vary across taxa, time and space. We determined whether recent fragmentation of Atlantic forest is causing population subdivision in a widespread and important Neotropical seed disperser: Artibeus lituratus (Chiroptera: Phyllostomidae). Genetic structure within highly fragmented forest in Paraguay was compared to that in mostly contiguous forest in neighbouring Misiones, Argentina. Further, observed genetic structure across the fragmented landscape was compared with expected levels of structure for similar time spans in realistic simulated landscapes under different degrees of reduction in gene flow. If fragmentation significantly reduced successful dispersal, greater population differentiation and stronger isolation by distance would be expected in the fragmented than in the continuous landscape, and genetic structure in the fragmented landscape should be similar to structure for simulated landscapes where dispersal had been substantially reduced. Instead, little genetic differentiation was observed, and no significant correlation was found between genetic and geographic distance in fragmented or continuous landscapes. Furthermore, comparison of empirical and simulated landscapes indicated empirical results were consistent with regular long‐distance dispersal and high migration rates. Our results suggest maintenance of high gene flow for this relatively mobile and generalist species, which could be preventing or significantly delaying reduction in population connectivity in fragmented habitat. Our conclusions apply to A. lituratus in Interior Atlantic Forest, and do not contradict broad evidence that habitat fragmentation is contributing to extinction of populations and species, and poses a threat to biodiversity worldwide.     

Gene flow simulations demonstrate resistance of long-lived species to genetic erosion from habitat fragmentation

Habitat fragmentation restricts the movement of individuals across a landscape. In terrestrial and aquatic systems, barriers to movement can modify population and community dynamics at local or regional scales. This study contrasted life history traits related to lifespan with habitat fragmentation to determine impacts on species population genetic structure in the Neuse River Basin, USA. For this, we simulated gene flow among evenly-spaced populations in a river network and tracked individual and population genetics for 200 years. The modeled scenarios represent a full cross between five life history strategies and four riverscapes representing varying degrees of fragmentation. The five life history strategies include species (based on freshwater mussels) with average lifespans ranging from 10 to 50 years and age at maturity from 2 to 6 years. The movement landscapes included a (1) panmictic, (2) stepping-stone landscape allowing movement to only neighboring populations during each dispersal event, (3) partially-fragmented landscape divided by dams currently in the network, and (4) fully-fragmented landscape. Results suggest species with shorter lifespans have higher population genetic structure in fragmented landscapes than species with longer lifespans. Furthermore, species with shorter lifespans in highly fragmented landscapes may be harboring genetic degradation or decline as allele fixation and loss. Although anthropogenic fragmentation of many river systems is only 100–200 years old, the simulation indicates that species can respond genetically in that period of time. Additionally, the time frame of the simulation suggests that genetic impacts of habitat fragmentation in some species present in the Neuse River Basin may not yet be manifesting and restoration activities could be successful.     

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.     

Fine-scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations

We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km(2). Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations < or = 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation.     

Genetic structure and seed-mediated dispersal rates of an endangered shrub in a fragmented landscape: a case study for Juniperus communis in northwestern Europe

Background

Population extinction risk in a fragmented landscape is related to the differential ability of the species to spread its genes across the landscape. The impact of landscape fragmentation on plant population dynamics will therefore vary across different spatial scales. We quantified successful seed-mediated dispersal of the dioecious shrub Juniperus communis in a fragmented landscape across northwestern Europe by using amplified fragment length polymorphism (AFLP) markers. Furthermore we investigated the genetic diversity and structure on two spatial scales: across northwestern Europe and across Flanders (northern Belgium). We also studied whether seed viability and populations size were correlated with genetic diversity.

Results

Unexpectedly, estimated seed-mediated dispersal rates were quite high and ranged between 3% and 14%. No population differentiation and no spatial genetic structure were detected on the local, Flemish scale. A significant low to moderate genetic differentiation between populations was detected at the regional, northwest European scale (PhiPT = 0.10). In general, geographically nearby populations were also genetically related. High levels of within-population genetic diversity were detected but no correlation was found between any genetic diversity parameter and population size or seed viability.

Conclusions

In northwestern Europe, landscape fragmentation has lead to a weak isolation-by-distance pattern but not to genetic impoverishment of common juniper. Substantial rates of successful migration by seed-mediated gene flow indicate a high dispersal ability which could enable Juniperus communis to naturally colonize suitable habitats. However, it is not clear whether the observed levels of migration will suffice to counterbalance the effects of genetic drift in small populations on the long run.     

Anthropogenic Habitats Facilitate Dispersal of an Early Successional Obligate: Implications for Restoration of an Endangered Ecosystem

Landscape modification and habitat fragmentation disrupt the connectivity of natural landscapes, with major consequences for biodiversity. Species that require patchily distributed habitats, such as those that specialize on early successional ecosystems, must disperse through a landscape matrix with unsuitable habitat types. We evaluated landscape effects on dispersal of an early successional obligate, the New England cottontail (Sylvilagus transitionalis). Using a landscape genetics approach, we identified barriers and facilitators of gene flow and connectivity corridors for a population of cottontails in the northeastern United States. We modeled dispersal in relation to landscape structure and composition and tested hypotheses about the influence of habitat fragmentation on gene flow. Anthropogenic and natural shrubland habitats facilitated gene flow, while the remainder of the matrix, particularly development and forest, impeded gene flow. The relative influence of matrix habitats differed between study areas in relation to a fragmentation gradient. Barrier features had higher explanatory power in the more fragmented site, while facilitating features were important in the less fragmented site. Landscape models that included a simultaneous barrier and facilitating effect of roads had higher explanatory power than models that considered either effect separately, supporting the hypothesis that roads act as both barriers and facilitators at all spatial scales. The inclusion of LiDAR-identified shrubland habitat improved the fit of our facilitator models. Corridor analyses using circuit and least cost path approaches revealed the importance of anthropogenic, linear features for restoring connectivity between the study areas. In fragmented landscapes, human-modified habitats may enhance functional connectivity by providing suitable dispersal conduits for early successional specialists.     

Does long‐distance pollen dispersal preclude inbreeding in tropical trees? Fragmentation genetics of Dysoxylum malabaricum in an agro‐forest landscape

Tropical trees often display long‐distance pollen dispersal, even in highly fragmented landscapes. Understanding how patterns of spatial isolation influence pollen dispersal and interact with background patterns of fine‐scale spatial genetic structure (FSGS) is critical for evaluating the genetic consequences of habitat fragmentation. In the endangered tropical timber tree Dysoxylum malabaricum (Meliaceae), we apply eleven microsatellite markers with paternity and parentage analysis to directly estimate historic gene flow and contemporary pollen dispersal across a large area (216 km²) in a highly fragmented agro‐forest landscape. A comparison of genetic diversity and genetic structure in adult and juvenile life stages indicates an increase in differentiation and FSGS over time. Paternity analysis and parentage analysis demonstrate high genetic connectivity across the landscape by pollen dispersal. A comparison between mother trees in forest patches with low and high densities of adult trees shows that the frequency of short‐distance mating increases, as does average kinship among mates in low‐density stands. This indicates that there are potentially negative genetic consequences of low population density associated with forest fragmentation. Single isolated trees, in contrast, frequently receive heterogeneous pollen from distances exceeding 5 km. We discuss the processes leading to the observed patterns of pollen dispersal and the implications of this for conservation management of D. malabaricum and tropical trees more generally.     

Population structure and genetic diversity of the threatened pygmy newt Triturus pygmaeus in a network of natural and artificial ponds

Pond physical characteristics (connectivity, hydroperiod) have shown to be highly relevant in explaining species presence, reproductive success, and survival in breeding-pond amphibians. However, few studies have addressed the influence that these factors may have on the genetic variability of pond populations. We examined genetic variation at 11 microsatellite loci in Iberian endemic, the pygmy newt (Triturus pygmaeus), from 58 breeding ponds in the Doñana National Park (Andalusia), including both temporary ponds and artificially deepened ponds that remain wet during the whole year. Temporary ponds are located in the North part of the region where the surrounding habitat-wet meadows-facilitates the connectivity among populations, whereas the deepest ponds (‘zacallones’) are located in the southern edge embedded in a matrix of unsuitable habitat (thickets and dry underbrush). We investigated genetic diversity and structure within and among ponds. Our results show that both regions (Doñana-North and Doñana-South) are well-differentiated and form two main clusters. We found higher genetic diversity within ponds from the North region, which also exhibited a higher degree of genetic admixture in comparison with populations from the southern edge. Although we found an isolation-by-distance pattern within each cluster, it arose due to the effect of a few isolated ponds located on the edge of each zone, suggesting the existence of substantial gene flow between ponds in the core area. According to our findings, landscape’s permeability to movement (pond connectivity) may constitute a more important factor than hydroperiod length in determining the genetic diversity and viability of pygmy newt populations in this area. Although Doñana populations show a good state, more peripheral and isolated populations present a more worrisome condition as a result of fragmentation and thus, require conservation efforts. Our study provides key insights that could help guide management practices of this threatened and poorly-studied salamander.

     

Population structure of spotted salamanders (Ambystoma maculatum) in a fragmented landscape

Understanding the impacts of landscape-level processes on the population biology of amphibians is critical, especially for species inhabiting anthropogenically modified landscapes. Many pond-breeding amphibians are presumed to exist as metapopulations, but few studies demonstrate the extent and consequences of this metapopulation structure. Gene flow measures may facilitate the construction of more realistic models of population structure than direct measures of migration. This is especially true for species that are cryptic, such as many amphibians. We used eight polymorphic microsatellite loci to determine the genetic population structure of spotted salamanders ( Ambystoma maculatum ) breeding at 17 ponds in northeastern Ohio, a landscape fragmented by roads, agriculture, urban areas and the Cuyahoga River. Using a variety of analyses (Bayesian clustering, F -statistics, AMOVA) we generated a model of salamander population genetic structure. Our data revealed patterns of genetic connectivity that were not predicted by geographical distances between ponds (no isolation by distance). We also tested for a relationship between population structure and several indices of landscape resistance, but found no effect of potential barriers to dispersal on genetic connectivity. Strong overall connectivity among ponds, despite the hostile habitat matrix, may be facilitated by a network of riparian corridors associated with the Cuyahoga River; however, high gene flow in this system may indicate a general ability to disperse and colonize beyond particular corridors.     

Fragmentation reduces regional‐scale spatial genetic structure in a wind‐pollinated tree because genetic barriers are removed

Gene flow strongly influences the regional genetic structuring of plant populations. Seed and pollen dispersal patterns can respond differently to the increased isolation resulting from habitat fragmentation, with unpredictable consequences for gene flow and population structuring. In a recently fragmented landscape we compared the pre‐ and post‐fragmentation genetic structure of populations of a tree species where pollen and seed dispersal respond differentially to forest fragmentation generated by flooding. Castanopsis sclerophylla is wind‐pollinated, with seeds that are dispersed by gravity and rodents. Using microsatellites, we found no significant difference in genetic diversity between pre‐ and post‐fragmentation cohorts. Significant genetic structure was observed in pre‐fragmentation cohorts, due to an unknown genetic barrier that had isolated one small population. Among post‐fragmentation cohorts this genetic barrier had disappeared and genetic structure was significantly weakened. The strengths of genetic structuring were at a similar level in both cohorts, suggesting that overall gene flow of C. sclerophylla has been unchanged by fragmentation at the regional scale. Fragmentation has blocked seed dispersal among habitats, but this appears to have been compensated for by enhanced pollen dispersal, as indicated by the disappearance of a genetic barrier, probably as a result of increased wind speeds and easier pollen movement over water. Extensive pollen flow can counteract some negative effects of fragmentation and assist the long‐term persistence of small remnant populations.     

Urbanisation versus agriculture: a comparison of local genetic diversity and gene flow between wood mouse Apodemus sylvaticus populations in human‐modified landscapes

Urbanisation and agriculture dramatically modify the landscapes available for use by wildlife, affecting key aspects of their ecology such as survival, foraging, predation, competition and reproductive success. Relatively little is known about the effects of urbanisation and agriculture on the genetic structure, gene flow and genetic diversity of wild species. Here, landscape genetic techniques were applied to compare local genetic diversity and gene flow between wood mouse populations in urban and arable landscapes. Using nine microsatellite markers, individuals were genotyped from six arable and seven urban sample sites. Inter‐population genetic differentiation was significantly greater in urban than arable habitat, while allele richness, private allele richness and heterozygosity were higher for arable sample sites, with varying degrees of significance. These suggest that urban habitat was sufficiently fragmented to limit gene flow. To test the effect of landscape features on gene flow, several cost‐distance measures were generated. Overland distance and Euclidean distance correlated best with inter‐population genetic differentiation in arable habitat, whereas distances that accommodated differences in habitat quality better explained differentiation in urban habitat. There was no evidence that margins adjacent to roads, rivers or railways facilitated gene flow. Together, the results indicate that urban landscapes expose wood mice to greater fragmentation in habitat quality than arable areas, leading to greater population isolation that is not mitigated by the presence of dispersal corridors.     

Do rivers function as genetic barriers for the plateau wood frog at high elevations?

Using the plateau wood frog Rana kukunoris from the Hengduan Mountains as a model system, we tested whether rivers form significant genetic barriers (the riverine barrier hypothesis) to high elevation amphibians. Samples were collected from eight sites across three major river drainages, the Min, the Dadu and the Yalong Rivers, and the population genetic structure of these frogs was evaluated with data from eight microsatellite DNA loci. A large amount of genetic structure was found, and the pairwise F _ST ranged from 0.022 to 0.508 and a global F _ST was 0.215. Both analysis of molecular variance and isolation by distance analysis suggested that rivers, mountain ridges and geographic distances all contributed significantly to the population structure. However, no single landscape has prominent barrier effect to the plateau wood frog populations. An assignment analysis using the computer program Structure grouped the eight populations into four population clusters, and no single type of landscape can sufficiently explain the clustering. In conclusion, rivers do not appear to be the leading genetic barriers for the plateau wood frog. The strong population genetic structure is likely the consequence of attributes of the species, as opposed to environmental fragmentation, and the barrier effect of the landscapes is largely swamped by the large amount of intrinsic population structure.     

Functional connectivity in replicated urban landscapes in the land snail (Cornu aspersum)

Urban areas are highly fragmented and thereby exert strong constraints on individual dispersal. Despite this, some species manage to persist in urban areas, such as the garden snail, Cornu aspersum, which is common in cityscapes despite its low mobility. Using landscape genetic approaches, we combined study area replication and multiscale analysis to determine how landscape composition, configuration and connectivity influence snail dispersal across urban areas. At the overall landscape scale, areas with a high percentage of roads decreased genetic differentiation between populations. At the population scale, genetic differentiation was positively linked with building surface, the proportion of borders where wooded patches and roads appeared side by side and the proportion of borders combining wooded patches and other impervious areas. Analyses based on pairwise genetic distances validated the isolation‐by‐distance and isolation‐by‐resistance models for this land snail, with an equal fit to least‐cost paths and circuit‐theory‐based models. Each of the 12 landscapes analysed separately yielded specific relations to environmental features, whereas analyses integrating all replicates highlighted general common effects. Our results suggest that urban transport infrastructures facilitate passive snail dispersal. At a local scale, corresponding to active dispersal, unfavourable habitats (wooded and impervious areas) isolate populations. This work upholds the use of replicated landscapes to increase the generalizability of landscape genetics results and shows how multiscale analyses provide insight into scale‐dependent processes.