Rapid sperm length divergence in a polygynandrous passerine: a mechanism of cryptic speciation?

Abstract When populations become geographically isolated, they begin to diverge in various traits and at variable rates. The dynamics of such trait divergences are relevant for understanding evolutionary processes as local adaptation speciation. Here we examine sperm body structures a polygynandrous songbird, the alpine accentor (Prunella collaris) between two allopatric high-altitude populations, Morocco Spain. diverged around 82 thousand years ago, estimated with coalescence-based phylogenetic analysis genome-wide single nucleotide polymorphisms. We found that birds areas had non-overlapping lengths, which suggests divergent female reproductive tract environments. Sperm length also showed an exceptionally low coefficient among-male variation, signal strong stabilizing selection imposed by competition. rate was almost twice rates most morphological traits, more than three times higher expected from literature data over similar generational timescale. This rapid evolution key has implications isolation ultimately Strong different optima allopatry predicts conspecific precedence disruptive sympatry, hence possible postcopulatory prezygotic barrier gene flow.