Abstract
Due to their isolated and often fragmented nature, range margin populations are especially vulnerable to rapid environmental change. To maintain genetic diversity and adaptive potential, gene flow from disjunct populations might therefore be crucial to their survival. Translocations are often proposed as a mitigation strategy to increase genetic diversity in threatened populations. However, this also includes the risk of losing locally adapted alleles through genetic swamping. Human‐mediated translocations of southern lineage specimens into northern German populations of the endangered European fire‐bellied toad (Bombina bombina) provide an unexpected experimental set‐up to test the genetic consequences of an intraspecific introgression from central population individuals into populations at the species range margin. Here, we utilize complete mitochondrial genomes and transcriptome nuclear data to reveal the full genetic extent of this translocation and the consequences it may have for these populations. We uncover signs of introgression in four out of the five northern populations investigated, including a number of introgressed alleles ubiquitous in all recipient populations, suggesting a possible adaptive advantage. Introgressed alleles dominate at the MTCH2 locus, associated with obesity/fat tissue in humans, and the DSP locus, essential for the proper development of epidermal skin in amphibians. Furthermore, we found loci where local alleles were retained in the introgressed populations, suggesting their relevance for local adaptation. Finally, comparisons of genetic diversity between introgressed and nonintrogressed northern German populations revealed an increase in genetic diversity in all German individuals belonging to introgressed populations, supporting the idea of a beneficial transfer of genetic variation from Austria into North Germany.
Highlights
Genetic admixture between populations is a widespread phenomenon that instantly increases the diversity of a population's gene pool and can enable a rapid adaptation to change in environmental conditions (Arnold & Kunte, 2017; Janes & Hamilton, 2017)
For all four German populations, we found positive D values indicating higher levels of admixture between the Austrian population and the German populations from Testorf, Högsdorf, Eutin and Dannau compared to Fehmarn, ranging from 0.048 to 0.288
We sampled five endangered northern B. bombina populations located in Germany and one southern B. bombina population from Austria and assessed the genetic consequences of human-mediated translocations of Austrian B. bombina populations into the range margin northern German populations
Summary
Genetic admixture between populations is a widespread phenomenon that instantly increases the diversity of a population's gene pool and can enable a rapid adaptation to change in environmental conditions (Arnold & Kunte, 2017; Janes & Hamilton, 2017). Even geographically close populations of B. bombina are often genetically distinct, likely due to high site fidelity and limited dispersal capability (Dolgener et al, 2012; Engel, 1996; Schröder et al, 2012). This is true for locally restricted and highly fragmented populations at the north- western margin of the species range, which runs from the south of the Swedish province Scania to the Baltic Sea through Denmark and Germany (Schleswig-Holstein, Niedersachsen, Sachsen-Anhalt) (Schröder et al, 2012). We further investigated transcriptome-wide genetic diversity of both introgressed and autochthonous populations
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