The world’s economically most important chelonians represent a diverse species complex (Testudines: Trionychidae: Pelodiscus)

Abstract

Pelodiscus is one of the most widely distributed genera of softshell turtles, ranging from south-eastern Siberia and Korea over central and southern China to Vietnam. Economically, Pelodiscus are the most important chelonians of the world and have been bred and traded in high numbers for centuries, resulting in many populations established outside their native range. Currently, more than 300 million turtles per year are sold in China alone, and the bulk of this figure comprises farmed Pelodiscus. Due to easy availability, Pelodiscus also constitutes a model organism for physiological and embryological investigations. Yet, diversity and taxonomy of Pelodiscus are poorly understood and a comprehensive investigation using molecular tools has never been published. Traditionally, all populations were assigned to the species P. sinensis (Wiegmann, 1834); in recent years up to three additional species have been recognized by a few authors, while others have continued to accept only P. sinensis. In the present study, we use trade specimens and known-locality samples from Siberia, China, and Vietnam, analyze 2,419 bp of mtDNA and a 565-bp-long fragment of the nuclear C-mos gene to elucidate genetic diversity, and compare our data with sequences available from GenBank. Our findings provide evidence for the existence of at least seven distinct genetic lineages and suggest interbreeding in commercial turtle farms. GenBank sequences assigned to P. axenaria (Zhou, Zhang & Fang, 1991) are highly distinct. The validity of P. maackii (Brandt, 1857) from the northernmost part of the genus’ range is confirmed, whereas it is unclear which names should be applied to several taxa occurring in the central and southern parts of the range. The diversity of Pelodiscus calls for caution when such turtles are used as model organisms, because the respective involvement of more than a single taxon could lead to irreproducible and contradictory results. Moreover, our findings reveal the need for a new assessment of the conservation status of Pelodiscus. While currently all taxa are subsumed under ‘P. sinensis’ and listed as ‘vulnerable’ by the IUCN Red List of Threatened Species, some could actually be endangered or even critically endangered.