No distinct barrier effects of highways and a wide river on the genetic structure of the Alpine newt (Ichthyosaura alpestris) in densely settled landscapes
Linear landscape elements such as roads, railways and rivers have been shown to act as barriers to dispersal and gene flow, hence impeding functional connectivity and increasing genetic differentiation between individuals or populations on opposite sides of the barrier. Such putative barriers act through a confluence of mechanisms, including crossing mortality, barrier avoidance and modifications to organisms’ effective dispersal patterns. Small, terrestrial animals such as amphibians are predicted to be vulnerable to the effects of such barriers given their limited locomotive performance and their dependence on spatially distinct breeding habitats. Here, we examined the effects of highways and a wide river on Ichthyosaura alpestris in three regions of northern Switzerland by measuring the genetic differentiation between local populations and describing the spatial genetic structure. Moreover, we estimated effective population sizes as an indicator for the susceptibility of populations to random genetic drift. Based on genetic differentiation, we found evidence to suggest that the highways and river acted as barriers to gene flow for the newt in the study regions, but results were inconsistent when ignoring breeding ponds with low samples sizes. Admixture-based genetic clustering suggested the delineation of the genotypes to rough regional clusters, with only weak structure inferred within these clusters. Thus, results suggest that at present, highways and rivers do not substantially affect the genetic structure of I. alpestris within northern Switzerland in a negative manner. Alternatively, the lack of a distinct genetic structure in regional newt populations may be explained by, e.g., large effective population sizes.
KeywordsAmphibians Barrier effect Functional connectivity Gene flow Landscape genetics
We thank Robin Winiger for assistance with lab work, Bettina Erne for assistance with field work, and Manuel Frei for teaching us newt-capture techniques. Benedikt Schmidt (KARCH) provided valuable input in various ways, while Maarten van Strien and Dorena Nagel inspired the R code applied. Comments of two anonymous reviewers are greatly acknowledged. We are indebted to the authorities and property owners in the cantons of Aargau, Thurgau and Zurich who gave us permission to sample on their grounds, as well as to the cantonal nature conservation and veterinary officers who provided sampling permits. This project was funded by the ETH Competence Centre for Environmental Sustainability (ETH-CCES, GeneMig project awarded to JB and FG).
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