Knowledge of Earth’s biodiversity remains insufficient for enumeration and conservation as evidenced by the Linnean and Wallacean shortfalls. The Linnean shortfall references that we have only described a small portion of the planet’s species, while the Wallacean shortfall points out our incomplete understanding of distributions, even for already described species. These shortfalls seem particularly relevent to invertebrates. Phylogenetic and phylogeographic studies provide insights into fundamental processes shaping biodiversity and help address both shortfalls. Apple snails (Ampullariidae), within the genus Pomacea, have high abundances, considerable diversity, and wide distributions in South America, which make for good candidates of biodiversity studies. Furthermore, many Pomacea spp. share similar gross morphologies that can make accurate species delineation difficult. Consequently, identification often requires an integrative systematic approach. Recent studies of apple snails uncovered cryptic species in southern Brazil and Uruguay, and preliminary data indicate hydrogeological events may have influenced their diversification. To understand the population structure and diversity of two Pomacea species (P. canaliculata and Pomacea sp., a putative cryptic species) in their overlapping native ranges of the Rio de la Plata Basin, we collected snails across Uruguay, sequenced a fragment of the COI gene and analyzed these sequences (N=579).
Using phylogenetic analyses, we confirmed the presence of Pomacea species, a putative cryptic species closely related to Pomacea canaliculata. Furthermore, phylogeographic analyses revealed that Pomacea sp. is widespread and occurring in nearly twice as many sites as P. canaliculata. To date, haplotype analyses recovered 82 haplotypes from Pomacea sp. (N = 351; h = 0.967; π = 0.01260) and 24 from P. canaliculata (N = 228; h = 0.799; π = 0.02659). The lack of any clear geographic structure of Pomacea sp. over such a wide range may indicate recent range expansions. Genetic variance was greater within populations (66%) than among populations (34%) for Pomacea sp. (AMOVA), but the opposite pattern held for P. canaliculata (44% within, 56% among). With advanced statistical analysis, we continue to investigate the degree of range expansion of these species following marine incursions during the Pleistocene. Our results reveal that Pomacea sp. is the dominant Pomacea species in Uruguay, a finding that starkly contrasts previously reported species distributions that possibly misidentified this species as P. canaliculata or P. maculata. The difficulty of morphologically identifying this cryptic species, combined with its range expansion, raises a concern regarding how long before this species ends up introduced elsewhere.