Phylogenetic Systematics and Distribution of Pomacea sordida (Swainson, 1823) and Pomacea intermedia (Férussac in Quoy & Gaimard, 1825) (Caenogastropoda: Ampullariidae)

Abstract

In contrast to their relative ecological and economic importance, many species of Ampullariidae remain poorly studied, and lack robust data needed to clearly circumscribe the species or understand their biogeographic distributions. A few, e.g., Pomacea maculata Perry, 1810 and P. canaliculata (Lamarck, 1822), have been well studied, in part because of their notorious reputations as invasive pests. Unfortunately, beyond broad phylogenetic studies, we know little about the relationships and distributions of the dozen or so other species with which these two well-known ampullariids have and continue to be confused. The ability to delimit such species not only has implications for invasion biology, but also for conservation of native species. The ampullariid Pomacea sordida (Swainson, 1823) is endemic to the state of Rio de Janeiro, Brazil. Recent molecular analyses revealed that several populations previously referred to as P. sordida, belong to another genetically distinct species, Pomacea intermedia (Férussac in Quoy & Gaimard, 1825), currently regarded as a junior synonym of P. sordida. To evaluate the validity of this previous study, we examined all of the material identified as P. sordida from the collection of the Institute Oswaldo Cruz and carried out additional surveys across the known distribution of these species. Phylogenetic analyses of COI sequences from 96 snails sequenced for this study, along with additional sequences from GenBank, recovered P. sordida and P. intermedia as sister taxa in a clade sister to P. flagellata (Say, 1829) and P. patula (Reeve, 1856). Surveys of aquatic habitats in the state of Rio de Janeiro recovered both species in allopatric populations with P. sordida primarily restricted to seven sites in the southwestern part of the state, whereas P. intermedia occurred in six sites in the central part of the state, northeast of P. sordida populations. Although cursory examination of male reproductive anatomy of these two species does not provide taxonomically informative characters that allow delineation of these two species, other traits e.g., juvenile shell characters, egg morphology, and kidney shape and arrangement, appear to be informative and provided necessary data to rescue P. intermedia from synonymy with P. sordida.