Fine‐scale population structure in a desert amphibian: landscape genetics of the black toad (Bufo exsul)

Abstract

Environmental variables can strongly influence a variety of intra- and inter-population processes, including demography, population structure and gene flow. When environmental conditions are particularly harsh for a certain species, investigating these effects is important to understanding how populations persist under difficult conditions. Furthermore, species inhabiting challenging environments present excellent opportunities to examine the effects of complex landscapes on population processes because these effects will often be more pronounced. In this study, I use 16 microsatellite loci to examine population structure, gene flow and demographic history in the black toad, Bufo exsul, which has one of the most restricted natural ranges of any amphibian. Bufo exsul inhabits four springs in the Deep Springs Valley high desert basin and has never been observed more than several meters from any source of water. My results reveal limited gene flow and moderately high levels of population structure (F(ST) = 0.051-0.063) between all but the two closest springs. I found that the geographic distance across the arid scrub habitat between springs is significantly correlated with genetic structure when distance accounts for topography and barriers to dispersal. I also found very low effective population sizes (N(e) = 7-30) and substantial evidence for historical population bottlenecks in all four populations. Together, these results suggest that the desert landscape and B. exsul's high habitat specificity contribute significantly to population structure and demography in this species and emphasize the importance of considering behavioural and landscape data in conservation genetic studies of natural systems.

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

“…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. Understanding the relationship between key habitat features and N e is thus another key component of a comprehensive conservation effort.…”

“…Quantifying the effects of landscape features on the effective population sizes of natural populations remains an important challenge in conservation genetics (Andersen et al 2004;Rowe and Beebee 2004;Beebee 2005;Wang 2009a). Effective population sizes (N e ) in wild animal systems vary widely (Scribner et al 1997;Crawford 2003;Hoffman et al 2004;Palstra and Rruzzante 2008) and determining N e for threatened and endangered species is a key component of their conservation and management (Andersen et al 2004;Rowe and Beebee 2004;Beebee 2005;Schwartz et al 2007).…”

“…In addition, if small effective populations tend to have small census populations, then measures of N e will also be informative regarding the demographic consequences of small populations. Thus, understanding the effects of environmental variables on the effective sizes of natural populations can contribute substantially to scientifically-informed conservation practices (Palstra and Rruzzante 2008;Wang 2009a).…”

“…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.…”

Microsatellite markers reveal genetic divergence among wild and cultured populations of Chinese sucker Myxocyprinus asiaticus

“…Under the SMM model, which is considered suitable for microsatellites (Luikart and Cornuet 1998), the demographic bottleneck was accompanied by a loss of genetic variability. These two small effective populations (13 samples from YB and 9 samples from YC) can occur for a variety of reasons including bottlenecks, genetic isolation, asymmetry in the proportions of males and females, and differences in the reproductive success of individuals (Tennessen and Zamudio, 2003;Myers and Zamudio, 2004;Wang, 2009).…”