Landscape genetics of the blotched tiger salamander (Ambystoma tigrinum melanostictum)

Abstract

The field of landscape genetics has great potential to identify habitat features that influence population genetic structure. To identify landscape correlates of genetic differentiation in a quantitative fashion, we developed a novel approach using geographical information systems analysis. We present data on blotched tiger salamanders (Ambystoma tigrinum melanostictum) from 10 sites across the northern range of Yellowstone National Park in Montana and Wyoming, USA. We used eight microsatellite loci to analyse population genetic structure. We tested whether landscape variables, including topographical distance, elevation, wetland likelihood, cover type and number of river and stream crossings, were correlated with genetic subdivision (F(ST)). We then compared five hypothetical dispersal routes with a straight-line distance model using two approaches: (i) partial Mantel tests using Akaike's information criterion scores to evaluate model robustness and (ii) the BIOENV procedure, which uses a Spearman rank correlation to determine the combination of environmental variables that best fits the genetic data. Overall, gene flow appears highly restricted among sites, with a global F(ST) of 0.24. While there is a significant isolation-by-distance pattern, incorporating landscape variables substantially improved the fit of the model (from an r2 of 0.3 to 0.8) explaining genetic differentiation. It appears that gene flow follows a straight-line topographic route, with river crossings and open shrub habitat correlated with lower F(ST) and thus, decreased differentiation, while distance and elevation difference appear to increase differentiation. This study demonstrates a general approach that can be used to determine the influence of landscape variables on population genetic structure.

Effective population size is strongly correlated with breeding pond size in the endangered California tiger salamander, Ambystoma californiense

“…These numbers, from very different sites with very different ecological conditions, suggest that movement among breeding sites is quite common in this species, and that the precise philopatry that is often ascribed to Ambystoma salamanders (Gamble et al 2007) may not hold for A. californiense. Interestingly, we found no evidence for isolationby-distance, which often occurs in amphibian systems (Funk et al 2005;Spear et al 2005;Wang et al 2009;Wang and Summers 2010). However, pairwise estimates of F ST among our ponds are consistent with estimates of gene flow and genetic clustering.…”

“…While most conservation genetics studies have focused on the importance of maintaining connectivity among populations, few have considered the ecological conditions necessary to maintain viable effective population sizes. Population connectivity is clearly important, both for sustaining genetic diversity and the complex source-sink dynamics that characterize many natural populations (Trenham et al 2001;Manel et al 2003;Storfer et al 2007;Spear et al 2005;Wang et al 2009). However, genetic diversity can also be protected by maintaining adequate effective population sizes Charlesworth and Willis 2009;Wang 2009a), and this may be particularly important as landscapes become fragmented and gene flow is interrupted.…”

“…While new methods in landscape genetics are increasingly sophisticated in their ability to assess the effects that the landscapes separating populations have on dispersal probability and the resulting population genetic structure (Manel et al 2003;Storfer et al 2007;Spear et al 2005;Giordano et al 2007;Wang 2010), few conservation and landscape genetics studies consider the effects that environmental variation has on intra-population variables such as demographic history and effective population size (Funk et al 1999;Driscoll 1999;Wang 2009a). For instance, in pond-breeding amphibians, substantial progress has been made in understanding the role of upland habitat in genetic structure and dispersal among populations (Trenham et al 2001;Wang et al 2009), but the effects of pond characteristics on population demography are relatively unknown.…”

Genetic drift and rapid evolution of viviparity in insular fire salamanders (Salamandra salamandra)

“…The F ST values obtained were higher than those documented in other fine-scale salamander studies (Cabe et al, 2007;Zamudio and Wieczorek, 2007;Purrenhage et al, 2009) and frog island populations (Lind et al, 2010), but showed similar levels of divergence to other amphibian population genetic studies covering larger regions (Spear et al, 2005;Savage et al, 2010). The similarities in genetic diversity and demographics among island and coastal populations (Table 1; Figure 3) underscore their similar histories, despite the current differences in connectivity to the mainland.…”

Syntopic frogs reveal different patterns of interaction with the landscape: A comparative landscape genetic study of Pelophylax nigromaculatus and Fejervarya limnocharis from central China

“…Throughout the development of landscape genetics, amphibians are at the forefront for detecting landscape barriers due to their commonly known characteristics of low vagility and high philopatry (Crosby et al., 2009; Cushman, 2006; Murphy et al., 2010; Spear, Peterson, Matocq, & Storfer, 2005). Often these two attributes influence the expectations regarding their patterns of genetic differentiation and prompt assumptions about landscape features that act as barriers to their subpopulations.…”