The role of pre‐ and post‐mating barriers in reproductive isolation in a dung beetle species complex

Abstract

AbstractPre‐ and post‐zygotic reproductive barriers are key components of reproductive isolation (RI) between taxa. Their timing of appearance and their strength can tell us about the underlying processes promoting differentiation between taxa in allopatry. Canthon cyanellus LeConte (Coleoptera: Scarabaeidae) represents a species complex that has diversified recently, and the species delimitation is still unclear. In this study, we performed experimental crosses to evaluate pre‐mating reproductive barriers between three subspecies of C. cyanellus: Canthon cyanellus cyanellus, Canthon cyanellus sallei, and Canthon cyanellus violetae. We further estimated post‐mating barriers by measuring fecundity and fertility in F1 and F2 generations in reciprocal crosses between two subspecies, C. c. cyanellus and C. c. sallei, and estimating the relative contribution of each barrier to total RI. Results showed that the subspecies are not strongly isolated overall, but asymmetric isolation was observed, with one cross accounting for 40% RI, whereas the other did not contribute to RI. Pre‐mating behavioral barriers accounted for a small fraction of total RI, whereas post‐mating (mostly post‐zygotic) barriers contributed to a larger extent. Fecundity and fertility in the F1 were higher than in parental populations, but this was strongly reduced in the F2. Our results suggest that diversification time between subspecies has been enough to accumulate genetic incompatibilities and indicate a faster accumulation of post‐ than pre‐zygotic reproductive barriers in this species complex.