Phylogeographic evidence for an African subspecies of spiny toad (Bufo spinosus)

Abstract

Molecular studies on the herpetofauna of the Western Palearctic have uncovered numerous genetic lineages that, pending evidence of evolutionary divergence, may warrant taxonomic recognition. In this study, we investigate whether the African population of the spiny toad (Bufo spinosus), known to bear unique mitochondrial haplotypes, represents a distinct species or subspecies from the European population. To address this, we analysed published mitochondrial barcoding sequences, nuclear gene fragments and allozyme genotypes, alongside new genomic data obtained from ultra-conserved elements, and assessed morphological variation among populations. All molecular datasets support genetic divergence between the African and European populations, likely stemming from a post-Messinian (Pliocene) transmarine vicariance event. Body size and morphology also statistically differ, but with broad overlap. Given that their level of divergence falls in the “grey zone of speciation” for Western Palearctic anurans, i.e. between typical species and subspecies thresholds, we conservatively describe the African population as a new subspecies of B. spinosus. Additionally, this subspecies features mitochondrial and nuclear differentiation between the westernmost (Morocco) and easternmost (Tunisia/eastern Algeria) ranges. While this pattern aligns with known phylogeographic breaks, we refrain from further taxonomic subdivision until broader sampling can rule out isolation-by-distance as the cause of the signal. Emblematic by its imposing size, the new African subspecies warrants immediate conservation attention, as its populations are potentially vulnerable, owing to their marked association with intensively impacted forest and riparian habitats.