Friday, April 5, 2013

[Testudology • 2013] One Extinct Turtle Species Less: Pelusios seychellensis Is Not Extinct, It Never Existed


Pelusios castaneus | hatchling, Comoé National Park, Ivory Coast

Figure 1. Distribution of Pelusios seychellensis (arrow) and P. castaneus. Introduced population of P. castaneus on Guadeloupe (Lesser Antilles) not shown. Inset: P. castaneus (hatchling, Comoé National Park, Ivory Coast). 
doi:10.1371/journal.pone.0057116

Abstract

Pelusios seychellensis is thought to be a freshwater turtle species endemic to the island of Mahé, Seychelles. There are only three museum specimens from the late 19th century known. The species has been never found again, despite intensive searches on Mahé. Therefore, P. seychellensis has been declared as “Extinct” by the IUCN and is the sole putatively extinct freshwater turtle species. Using DNA sequences of three mitochondrial genes of the historical type specimen and phylogenetic analyses including all other species of the genus, we provide evidence that the description of P. seychellensis was erroneously based on a widely distributed West African species, P. castaneus. Consequently, we synonymize the two species and delete P. seychellensis from the list of extinct chelonian species and from the faunal list of the Seychelles.

Figure 2. Dorsal (left) and ventral aspect (right) of the lectotype of Pelusios seychellensis.

One Extinct Turtle Less: Turtle Species in the Seychelles Never Existed

 — The turtle species Pelusios seychellensis regarded hitherto as extinct never existed. Scientists at the Senckenberg Research Institute in Dresden discovered this based on genetic evidence. The relevant study was published today in the journal PLOS ONE.

Turtles are the vertebrates under the greatest threat. Among the approximately 320 turtle species, the species confined to islands have been especially hard hit -- humans have caused the extinction of a whole number of species. One of them -- or at least it was thought so -- is the Seychelles mud turtle Pelusios seychellensis. Just three specimens were collected at the end of the 19th century; they are still kept at the Natural History Museum in Vienna and the Zoological Museum in Hamburg.

Despite an intensive search for this species, which was declared as "extinct" by the International Union for Conservation of Nature (IUCN), no further specimens have been found since those in the 19th century. "Consequently, it was assumed the species had been exterminated," says Professor Uwe Fritz, director of the Museum of Zoology at the Senckenberg Natural History Collections in Dresden. The Dresden biologist states quite clearly that this is not true. "We have examined the DNA of the original specimen from the museum in Vienna and discovered that these turtles are not a separate species."

The genetic analyses have shown that this supposed Seychellois species is in reality another species, Pelusios castaneus, that is widespread in West Africa. "The species Pelusios seychellensis has therefore never existed," adds Fritz. "In fact, for a long time researchers were amazed that the supposed Seychelles turtles looked so deceptively similar to the West African turtles. But due to the great geographic distance, it was thought this had to be a different species, which is why the assumed Seychelles turtles were also described as a new species in 1906."

The West African mud turtle Pelusios castaneus acquired an “extinct Doppelganger” from the Seychelles due to a scientific error.


Citation: Stuckas H, Gemel R, Fritz U. 2013. One Extinct Turtle Species Less: Pelusios seychellensis Is Not Extinct, It Never Existed. PLoS ONE 8(4): e57116. doi:10.1371/journal.pone.0057116

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