The roles of allopatric fragmentation and niche divergence in intraspecific lineage diversification in the common midwife toad (Alytes obstetricans)

Aim: Understanding the roles of allopatric fragmentation and niche divergence in intraspecific lineage diversification is central to our comprehension of how new species arise and evolve. Here we integrate an extensive multilocus dataset with species distribution models to address these topics in genetically differentiated population lineages of the common midwife toad (Alytes obstetricans). Location: Iberian Peninsula, Western Europe. Methods: We genotyped 965 individuals from 142 localities at 12 microsatellite loci to finely delineate the ranges of population lineages in A. obstetricans. We then built ecological niche-based models for each lineage and tested for niche overlap, equivalency and similarity based on PCA-env analyses. We also investigated the relationship between genetic and environmental distances across lineages. Results: We recovered seven differentiated genetic clusters, with mostly different (sometimes nonoverlapping) niches. However, niches are not more divergent than expected given the largely allopatric ranges of population lineages. We found no significant isolation by environment within lineages, with genetic distances mostly explained by geographical distances. Main conclusions: Allopatric fragmentation in A. obstetricans resulted in (sometimes highly) different niches in intraspecific population lineages. Within lineages, isolation by distance is the major driver of patterns of genetic variation. Our study highlights the importance of incorporating intraspecific genetic structure into species distribution models to explore spatial patterns of genetic diversity in terms of their underlying processes.