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.

Molecular phylogeny and trait evolution of Madeiran land snails: radiation of the Geomitrini (Stylommatophora: Helicoidea: Geomitridae)

“…Molecular analyses in the past 15 years have led to numerous systematic rearrangements in helicoid land snails (Wade et al, 2007; Hugall and Stanisic, 2011; Gómez‐Moliner et al, 2013; Razkin et al, 2015; Neiber et al, 2017; Sei et al, 2017). Moreover, it could be shown that reconfigurations, transformations and reductions of the dart apparatus have evolved many times in parallel in this superfamily (Hirano et al, 2014; Köhler and Criscione, 2015; Walther et al, 2016, 2018; Neiber and Hausdorf, 2017; Neiber et al, 2017, 2018a; Chueca et al, 2018), and it may even differ considerably among closely related taxa or within a single species (Korábek et al, 2015; Neiber and Hausdorf, 2015; Kruckenhauser et al, 2017; Zopp et al, 2017; Neiber et al, 2018b). In Geomitrini, the calcareous dart has been lost and the dart sac or the accessory sac has been transformed to a hollow tube, the appendicula.…”