Surprising Genetic Similarity of Balkan Turtles Suggests They are Very Good Swimmers

Wide geographical barriers would, seemingly, prevent a small animal like the Balkan pond turtle from becoming a widely distributed animal.

But new research into the freshwater turtles, formally known as Mauremys rivulata, reveals that despite geophysical barriers, the turtles are remarkably genetically similar throughout their distribution range.

The turtles are found in lakes and streams in the region of the Eastern Mediterranean, from southeast Europe and Greece to western Turkey and as far as Lebanon, Israel, Syria and the islands of Crete and Cyprus.

Their wide distribution and genetic similarity suggests that the turtles crossed hundreds of kilometers of sea to establish themselves across such a wide geographic range, according to scientists at the Senckenberg Research Institute in Dresden, Germany.

Because of the many geographical barriers in the range of this freshwater turtle -- especially the Aegean Sea -- we assumed that there would be many genetically different populations. This was based on the consideration that there was no gene flow between the isolated distribution patches, as the sea divides the populations," said Uwe Fritz, managing director at Senckenberg Dresden.

But the Senckenberg team discovered that the far-flung turtle populations have surprising genetic similarities.

"The astonishing thing is that even turtles living at great distances from each other display an almost identical genetic pattern, for instance, in southeast Europe and Asian Turkey" Fritz said.

One possible explanation is that the turtles were transported by humans across the Mediterranean. But that seems unlikely, the researchers said.

"One idea is that the turtles were brought to the different regions by humans, which meant that the gene pool could mix constantly," said lead study author Melita Vamberger. "Yet in contrast to other turtles, Mauremys rivulata was never popular as food, because these animals stink terribly. There is therefore no obvious reason why these turtles should have been transported in such large numbers."

This only leaves the turtles themselves as the plausible means for their wide distribution.

"We assume that this freshwater turtle is dispersed across the sea," Vamberger said. "It is likely that turtles are swept repeatedly from their habitats in coastal swamps into the sea by storms. They can obviously survive for a long time in the sea, long enough until they are washed onto some shoreline somewhere. And this occasional exchange is sufficient!"

The researchers report their findings in the journal Zoologica Scripta.