The genus Potamolithus Pilsbry, 1896 (Gastropoda: Tateidae) on the Somuncurá Plateau, Patagonia, Argentina

Phylogeography and molecular species delimitation reveal cryptic diversity in Potamolithus (Caenogastropoda: Tateidae) of the southwest basin of the Andes

The species of the genus Potamolithus inhabiting the southwestern basin of the Andes are difficult to distinguish due to small size and similar shell morphology. Only Potamolithus australis and Potamolithus santiagensis have been traditionally recognized in this region, but the occurrence of several morphologically similar undescribed populations could increase the regional richness. Here we delimit described and potentially undescribed cryptic species of the genus using partial sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Network analysis and diversity indices inferred six highly differentiated haplogroups, many of them sympatric and widespread in the study area. Phylogeographic analyses suggest a scenario of recent diversification and the occurrence of multiple refuges during the successive Pleistocene glaciations. Phylogenetic analysis also recovered six major clades that showed no relationship with physiography. Species delimitation analyses consistently recognized three or four candidate species apart from P. australis and P. santiagensis. Divergence times indicate that speciation of Chilean Potamolithus began at the end of the Pliocene, probably driven by climatic rather than geographic events. Considering the high inter- and intra-basin genetic diversity, conservation efforts should be focused on protecting sympatric taxa in the basins with the highest species richness.

Two new freshwater planarian species (Platyhelminthes: Tricladida: Dugesiidae) partially sympatric in Argentinean Patagonia

Girardia Ball, 1974 is the most diverse and widely distributed genus of the family Dugesiidae (Platyhelminthes: Continenticola) in the Neotropical region. Seven out of the 52 species of the genus are known for Argentina. The Somuncurá Plateau is a region in northern Patagonia with several endemic flora and fauna, but little is known about the free-living Platyhelminthes. We describe two new species of Girardia partially inhabiting in sympatry in the Somuncurá Plateau: Girardia somuncura sp. nov. and Girardia tomasi sp. nov. The identification criteria that we followed was an integrative taxonomic approach based on morphological and molecular data. Thus, we used anatomical features focused on the reproductive system, together with a phylogenetic analysis, using a mitochondrial (COI barcode region) genetic marker. This study is the first phylogenetic analysis of the genus Girardia in which we include the southernmost representatives of America here described, thus making it possible to incorporate them in global phylogenies.

Morphological and molecular analysis of cryptic native and invasive freshwater snails in Chile

Species delimitation in minute freshwater snails is often difficult to perform using solely shell morphology. The problem intensifies when invasive species spread within the distribution range of morphologically similar native species. In Chile, the Truncatelloidean snails are represented by the native genera Heleobia and Potamolithus plus the invasive mudsnail Potamopyrgus antipodarum, which can easily be confused. Using an integrative approach, we performed molecular phylogenetic analysis and studied reproductive and morphological features to identify superficially similar forms inhabiting the central area of the country. Truncatelloidean snails were identified in 40 of 51 localities sampled, 10 containing Potamopyrgus antipodarum, 23 Heleobia and 7 Potamolithus. Based on these results and previously published data, the known distribution of the mudsnail in Chile encompasses 6 hydrological basins, including 18 freshwater ecosystems. The finding of the mudsnails in several type localities of native species/subspecies of “Heleobia” that were not find in situ suggests species replacement or significant extinction of native fauna, a hypothesis supported by the restudy of type material that shows that endemic forms belong to the genus Potamolithus. This study shows the usefulness of integrative taxonomy not only resolving complex taxa with cryptic morphology but also measuring the extent of an ongoing invasion.

Diversity of Potamolithus (Littorinimorpha, Truncatelloidea) in a high-diversity spot for troglobites in southeastern Brazil: role of habitat fragmentation in the origin of subterranean fauna, and conservation status

The Alto Ribeira karst area, southeastern Brazil, is a high-diversity area for troglobites. Three species of freshwater gastropodsPotamolithusoccur in the area:P.ribeirensis, only found in epigean waters at the Iporanga and Ribeira rivers;P.troglobius, which is endemic to the Areias cave system; andP.karsticus, a troglophilic species from Calcário Branco Cave and an epigean stream nearby. We investigated their distribution based on shell morphology and internal anatomy of epigean species, troglophilic populations, and troglobitic species. Distribution patterns ofPotamolithuswere compared to those of other aquatic taxa from the region (such as crustaceans and fishes). Besides the three species already described for the region, we recorded 12 additional ones, for a total of 15 species/morphs (six troglobites, seven troglophiles, and two epigean).Potamolithusspp. are restricted to micro-basins and/or caves, showing small areas of distribution and probably a high degree of endemism. Geomorphology (irregular landscape, with limestone outcrops intercalated with insoluble rocks, which probably act as geographic barriers for cave populations), paleoclimatic evidence, and ecological/biological factors, such as the low degree of mobility of these gastropods (sedentary habit), explain the distributional patterns. We observed troglomorphisms such as reduction/absence of eyes and pigmentation (body and periostracum), and a coiled intestine. Apparently, there is no cause-and-effect between miniaturization and intestine coiling forPotamolithus, in contrast to observations for other cave snails.Potamolithussnails are threatened in the region due to water pollution, uncontrolled tourism, and overcollection.