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Who am I – and if so, how many? DNA sequences reveal the true identity of the softshell turtle Pelodiscus
23 September 2011
Senckenberg Research Institute and Natural History Museum
Dresden, 23 September 2011. A research team from the Senckenberg Research Institute Dresden has identified many different genetic lineages in the softshell turtle genus Pelodiscus, representing different species. Traditionally it has been assumed that only the species Pelodiscus sinensis belonged to the genus examined. As a foodstuff, Chinese softshell turtles are the most economically important turtles in the world, with an annual trade volume of many hundreds of millions of specimens. The accompanying study is being published today in the "Journal of Zoological Systematics and Evolutionary Research".
It is probably safe to say that none of the 300 million turtles that land on a plate in China each year are particularly interested to know the species to which they belong, but for scientists the discovery of different genetic lineages is of enormous significance. Due to its ease of breeding the turtle is often used as a model organism for embryological and physiological studies, so that a correct identification of the species is of paramount importance, not only in the fields of taxonomy and systematics.
Prof. Uwe Fritz, one of the Dresden authors of the study, confirms this: “While until now these turtles have been used as models in many scientific works, nobody actually knew what species they were. This led to considerable contradictions or non-reproducible results, because different species were used in different publications.”
The Chinese softshell turtle (Pelodiscus sinensis) is a strange looking animal: its shell is – as the name already suggests – soft, the long neck is flexible enough to allow the reptile even to see behind himself, and the trunk-like nose proves to be an excellent snorkel in shallow waters. Around the world there are more than 300 different turtle species, only 30 of which have a soft shell. Instead of an ossified shell, the softshell turtles, with a length of up to 30 centimetres, have a leather-like, flexible skin on their back and belly.
Together with his colleague Heiko Stuckas, Fritz examined the DNA of two 180-year-old softshell turtle shells from the Berlin Natural History Museum (Museum für Naturkunde). In 1834 the greatly shrunken and dried-out samples had served the German zoologist Arend Friedrich August Wiegmann as a basis for describing the species Pelodiscus sinensis.
Tiny pieces of tissue were removed from the shells by the Dresden researchers and parts of the genetic makeup of the turtles were defined with the help of the most up-to-date techniques. What is promising here is above all the analysis of the mitochondrial DNA, as these are present to a much greater degree compared to the DNA of the cell nucleus, thus minimising conservation problem.
Unfortunately, the attempt to gain DNA from the first turtle shell failed completely – the remnants of the animal were simply too old and too dried out. However, the second shell proved to be a great success for the research team! The analysis of the DNA sequences led to the conclusion that the genus Pelodiscus contains at least four and not – as previously believed – one species. For the first time, and with the help of the sequences from the Berlin sample, which is more or less the “original standard” for the species Pelodiscus sinensis, it could be clarified which of the four species is actually the “real” Chinese softshell turtle.
This finding is not only of great importance to the field of science; the turtles themselves can also benefit. At present all species that are collated under Pelodiscus sinensis have been placed on the red list of endangered species by the International Union for Conservation of Nature and Natural Resources (IUCN). However, some of the “newly discovered” species could actually be considered to be even more seriously endangered at present and may therefore enjoy greater protection.
In future, due to the results of the research, the different species will no longer be “lumped together” – at least by scientists – but rather can now be named precisely.