diamondback terrapin
May 6, 2014

Turtle Genetics Plays A Key Role In Conservation Of Diamondback Terrapins

April Flowers for redOrbit.com - Your Universe Online

There is an old saying that one should never judge a book by its cover, and that seems to be true for turtles as well. This diamondback terrapin is known for the diverse patterns intricately grooved into its shell. The pattern makes the turtle instantly recognizable, however it does not solve the problem of conservation for these coastal animals. That answer, according to a new study from the United States Geological Survey (USGS), is going to come from the genetic diversity beneath those shells.

Currently, there are seven recognized subspecies of the terrapin, which spends its entire life in coastal marshes and mangroves. Scientists recognize these subspecies based on external traits such as skin color and shell shape, and each species occupies a strip of the eastern seaboard or Gulf of Mexico coastline. Their natural habitat ranges from as far south as Texas to as far north as Massachusetts. In several locales, they are listed as either endangered (Rhode Island), threatened (Massachusetts) or a species of special concern.

Fragmentation of their coastal habitats and an increasingly patchy swath of coastal marshes have created a challenging environment for the turtles' to find each other and continue interbreeding. Many of the states where these animals live are investigating ways to address the issue.

“Before now, it was not clear how terrapin genetics varied across the range,” said Kristen Hart, a USGS research ecologist, in a recent statement. “Understanding this variation across the landscape helps land managers develop conservation plans. For example, they may pinpoint areas where habitat protection can be supplemented with migration corridors.”

Migration corridors are maintained by conservation authorities — through habitat restoration, regulatory policies, and other means — to allow wildlife to continue to breed based on their historic patterns. The corridors connect two or more prime areas of habitat, so understanding where to construct them is key to maintaining the terrapins' existing natural diversity and keep their overall population numbers robust, explained Hart.

“Diversity loss can be a silent threat to many species,” explained Maggie Hunter, a USGS research geneticist. “The threat to long-term survival of terrapins occurs if they become separated into isolated groups. Isolation can affect their overall survival several generations down the line.”

Conservation managers and scientists must understand the existing genetic variations between the species first, however, before knowing how to support a healthy mix of genetic diversity.

“Healthy interbreeding doesn’t mean that turtles from Maine have to interbreed with those from Texas,” explained Hunter. “Once managers know where ‘natural breaks’ in populations occur, they can focus on keeping terrapin populations healthy by enabling reproduction within each of those distinct groups.”

Hart and Hunter collaborated with USGS research geneticist Tim King to use DNA samples obtained from the blood of nearly a thousand terrapins to study the breeding patterns and identify those natural genetic breaks. King decoded strands of DNA for comparative purposes that revealed variations in 12 genetic markers. The terrapins were assigned into genetically similar groups using these markers as criteria for the differentiation.

Only four genetically distinct populations were found. The researchers were surprised by this, as there are seven recognized subspecies — meaning that the genetic "natural breaks" do not correspond to the range of those subspecies.

The researchers say that their findings have at least one more potential benefit. Terrapin were considered a delicacy as recently as the 1920s, and sometimes still turn up in food markets around the world. The genetic mapping will allow wildlife agencies to return rescued turtles to their correct habitat.

The results of this study were published in a recent issue of Conservation Genetics.