Increasing the evolutionary potential of threatened species - genetic and genomic insights from the common midwife toad (Alytes obstetricans) at its range limits

Abstract

Anthropogenically induced habitat modification and climate change are fundamental drivers of biodiversity declines, reducing the evolutionary potential of species populations, particularly at the limits of their distribution ranges. Supportive breeding or reintroductions of individuals are often made to replenish declining populations, sometimes informed by genetic analysis. However, most approaches utilised (i.e. single locus markers) do not have the resolution to account for local adaptation to environmental conditions, a crucial aspect to consider when selecting donor and recipient populations. Here, we incorporate genetic (microsatellite) and genome-wide SNP (ddRAD-seq) markers, accounting for both neutral and adaptive genetic diversity, to inform the conservation management of the threatened common midwife toad, Alytes obstetricans at the northern and eastern edges of its range in Europe. We find geographically structured populations (n=4), weak genetic differentiation and fairly consistent levels of genetic diversity (observed heterozygosity and allelic richness). Categorising individuals based on putatively adaptive regions of the genome showed that the majority of populations are not strongly locally-adapted. However, several populations demonstrate high numbers of private alleles in tandem with local adaptation to warmer conditions and rough topography. Combining genetic diversity and local adaptations with estimates of migration rates, we develop a decision-making framework for selecting donor and recipient populations which maximises the geographic dispersal of neutral and adaptive genetic diversity. Our framework is generally applicable to any species, but especially amphibians, so armed with this information, conservationists may avoid the reintroduction of unsuitable/maladapted individuals to new environments and increase the evolutionary potential of populations within species.