Polymorphism of a genital organ under sexual selection in Monacha kuznetsovi from the Caucasus (Gastropoda: Hygromiidae)

Abstract

During mating the dart apparatus of the land snail group Helicoidea transfers an allohormone that increases paternity success. Thus, this organ is under sexual selection. Despite this selective advantage, the dart sac has independently been lost in many lineages in the Helicoidea, presumably because natural selection counteracts sexual selection. However, the selective pressures that result in the loss of the organ have not been examined experimentally because most species show no variation in the presence or absence of the dart sac. Using nuclear multilocus data and mitochondrial sequences, we show that a so far misidentified morph of the genus Monacha without appendicula, a homologue of the dart sac, is conspecific with M. kuznetsovi with appendicula. This is only the second case of polymorphy with regard to the presence or absence of the dart sac or its homologue in the Helicoidea. Monacha kuznetsovi might therefore be a suitable model organism to study how the interplay between sexual selection and natural selection may affect the evolution of the genital organs.