The change in genetic diversity down the core‐edge gradient in the eastern spadefoot toad (Pelobates syriacus)

Abstract

Several hypotheses are available to predict change in genetic diversity when approaching peripheral populations. We used the eastern spadefoot toad in Israel as a model system to examine these hypotheses using population genetics analyses and network theory. Our results contradicted most of the predictions from the 'abundant centre' model, that edge populations should have lower density and lower genetic diversity than core populations. Furthermore, dispersal rate between core and peripheral populations is expected to be asymmetric, mostly directed outwards from the core population, but we did not detect such a trend. Our data did not support the hypothesis of no change or a non-linear change in genetic diversity towards the range edge. However, our results did fit the Fisher (The Genetical Theory of Natural Selection, Clarendon Press, Oxford, 1930) hypothesis, which predicts increase in genetic variability from core to edge of distribution. We attributed this finding to the much harsher climatic and abiotic conditions at the edge, which must be tolerated over generations by both tadpoles and post-metamorphic individuals in this region. Finally, our results have significant conservation implications for the survival of this species in Israel, where it is critically endangered. We identified two distinct communities, which are genetically linked through two specific rain pools in the Upper Galilee. Details on the spatial subdivision of this species are cardinal for future management and restoration of temporary wetlands in Israel.

The Habitats, Burrowing Behavior, Physiology Adaptation and Life Cycle of Spadefoot Toads (<i>Pelobates syriacus, Boettge</i>r, 1869) at the Southern Limit of Its Distribution in Israel

“…According to the results of the present study, the selection and adaptation to ecological conditions is not done according to the aquatic phase of Spadefoot toads but following metamorphosis. This hypothesis, which is supported by relatively many studies on the conditions of larvae growth of Spadefoot toads [14], shows that the water analysis of larvae is suitable for other amphibians in Israel, and that the distribution of Spadefoot toads is in drier conditions [21]. The burrowing behavior of metamorphosed Spadefoot toads preventing dehydration, as was found in the present study, is very important adaptation to terrestrial life.…”

“…The genetic variation among their populations was studied in the southern area of the Mediterranean shoreline [11] [12]. Nevo [13] suggested that Pelobates was best explained by the environmental variability model based on selection for homozygosity as an adaptive strategy in the relatively constant and narrow subterranean niche.…”

Population at the edge: increased divergence but not inbreeding towards northern range limit in Acer campestre

“…In particular, it is well recognised in peripheral populations as compared with central ones (the 'central-marginal' genetic pattern) (reviewed in Eckert et al 2008; but see, e.g. Munwes et al 2010). According to the theoretical predictions, less genetically diverse populations are often characterised by lower viability (Frankham 2003;Reed and Frankham 2003;Aguilar et al 2008) and/or adaptability (Young et al 1996, Willi et al 2006.…”

DNA variations of the green toad Pseudepidalea viridis (syn. Bufo viridis) from various habitats

“…This study supports the hypothesis that various ecological conditions in a relatively small area have little effect on genetic variations, but relatively greater molecular variations were found at greater distances, e.g., in comparison with populations from different countries. Comparisons with other species in Israel showed that Salamandra infraimmaculata (Goldberg et al 2009a), Triturus vittatus vittatus Degani 2007, 2008;Pearlson et al 2010), and Pelobates syriacus (Munwes et al 2010) were more stable and did not have as high a migration rate as was found in P. viridis that used different winter pools (Degani and Kaplan 1999).…”