Investigating the species diversity of Planorbella and Helisoma (Gastropoda: Hygrophila: Planorbidae) in Manitoba

Abstract

Species-level resolution is lacking for freshwater gastropods in Family Planorbidae, with factors like cryptic species, phenotypic variation, and potential misidentifications confounding estimates of biodiversity. To characterize the diversity of five nominal planorbid species (four Planorbella and one Helisoma), I compared descriptive morphology-based identifications to phylogenetic (COI gene) and geometric morphometric analyses of shell shape. I recovered five genetically distinct clades though two clades may contain cryptic species. Shell shape analysis confirmed morphological overlap between some species and confirmed that shell-based identifications can be problematic for species-level identification. For each of the five clades, I sequenced the complete mitogenomes and nuclear rRNA repeat regions. Comparisons among the mitochondrial (COI gene and mitogenome) and nuclear gene phylogenies (concatenated 18S/28S, ITS1-5.8S-ITSII, rRNA repeat region) resulted in some incongruence suggesting past hybridization between two species. These findings show that an integrative approach to species delimitation is essential for understanding the biology of freshwater gastropods.