Haldane's rule in Carabus: interspecific mating between Carabus punctatoauratus and Carabus splendens using experimental tests and molecular markers

Carabus splendens Olivier and Carabus punctatoauratus Germar (Coleoptera: Carabidae: Carabini) are ground beetles found in sympatry in forests in the eastern Pyrénées. We investigated potential interspecific mating using crossing experiments under controlled laboratory conditions and paternity analyses based on microsatellite markers. We show that under laboratory conditions, interspecific mating produces viable and fertile offspring. Although hybrid males were sterile, females were fertile and thus reproductive isolation between the two species is far from complete. We discuss the results in relation to species integrity due to pre- or post-zygotic barriers, and compare them to a previous study quantifying hybridization between the two species in natural populations.