What Is the Population Structure of Poecilogonic Species? Evidence From Large-Scale Genotyping in a Neogastropod...

Dispersal of marine benthic invertebrates is typically dependent on the developmental mode of their pelagic larvae, which can be prolonged and based on plankton feeding (planktotrophic), or short and rely on the nutrients from the egg (non-planktotrophic). The uncommon poecilogonic species can commit to both developmental modes, with remarkable implications for their population genetics, not yet fully investigated. In this study, we obtained reduced-representation genome-wide SNP data for three species of the neogastropod genus Raphitoma Bellardi, 1847 from the Mediterranean, including the putatively poecilogonic species Raphitoma philberti (Michaud, 1829) and R. laviae (R. A. Philippi, 1844). A total of 80 samples were sequenced to test the poecilogony and analyse the population genetics of R. laviae. Although a certain degree of segregation was highlighted between the planktotrophic and non-planktotrophic samples in both species, they were ultimately found within conspecific bounds, confirming poecilogony. A set of loci that split samples with different development was identified, suggesting that a genetic component may be involved in poecilogony in both species. The population genetics of R. laviae fit patterns of both long- and short-dispersal species: in Corsica, with only planktotrophic developers, no geographic structure was detected, whereas in Croatia, with only non-planktotrophic developers, the geographic structure was present among localities 15-40 km apart. Notably, the species delimitation based on genome-wide SNP data was contrasting with the one assessed in past studies, reiterating that a solid taxonomy (still not achieved) is paramount to correctly interpret the evolution of larval development in this group.