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

Maria Elina Bichuette,Eleonora Trajano

doi:10.3897/subtbiol.25.23778

Abstract

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.

Highlights

Neritimorpha gastropods, and mainly neogastropods, have been recorded in the subterranean realm (e.g., Theodoxus subterrelictus Schütt, 1963; Georissa papuana Bernasconi, 1995)
We present the results of this study, as a contribution to knowledge of the diversity of subterranean aquatic gastropods and morphological specializations of troglobites, by comparing epigean species, troglophilic populations, and troglobitic species
Temperatures are above 22 °C in the warmest month (January) and below 4 °C in the coolest month; mean annual temperature is around 19–20 °C in the Parque Estadual Turístico do Alto Ribeira (PETAR), and 17–18 °C in the upper Parque Estadual Intervales (PEI), where collections were carried out (Köeppen 1948)

Summary

Introduction

Neritimorpha gastropods, and mainly neogastropods, have been recorded in the subterranean (hypogean) realm (e.g., Theodoxus subterrelictus Schütt, 1963; Georissa papuana Bernasconi, 1995). Other frequent specializations reported for troglobitic truncatelloids are miniaturization, and, as a consequence, the complex coiling of the intestine and a lack, or reduction, of the ctenidium and the semen receptacle (Hershler and Holsinger 1990). This miniaturization is proposed as an adaptive characteristic to environments with poor food supplies (see Sanders and Allen 1973, Hershler and Longley 1986), or as an ancestral characteristic present in epigean relatives (exaptation, sensu Arnold 1994)

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Discussion

Conclusion