Though declining, threatened rattlers show little inbreeding

Eastern massasauga rattlesnakes (Sistrurus catenatus) are declining throughout most of their range, but in Illinois, a 10-year genetics study found a lack of inbreeding among the rattlers there, offering hope for the threatened snake’s recovery.

“We really expected to see a high level of inbreeding,” said Illinois Natural History Survey postdoctoral researcher Sarah J. Baker, who led the new research, which was published in the American Society of Ichthyologists and Herpetologists’ journal Copeia. “The population is small. It’s clustered into smaller subunits and separated by roads and cropland and a lake.”

Despite these small, fragmented populations, Baker said, the snakes’ showed a high amount of genetic diversity. The study did find, however, that some rare versions of genes that were apparent when the study began in 2002 had disappeared by 2012, suggesting that a loss of genetic diversity and inbreeding might be imminent.

Eastern massasaugas live in wet areas, including prairies, marshes and alongside lakes and rivers, in a range that stretches from New York and Ontario to eastern Iowa. Federally listed as threatened, they are listed as endangered, threatened or a species of concern in every state and province where they appear.

In Illinois, where they are state listed as endangered, fewer than 200 individuals are believed to remain in scattered populations, the largest of which consists of an estimated 26 to 69 individuals.

“Their population has been declining everywhere,” Baker said. In Illinois, they’ve been impacted by the conversion of the landscape to cropland and the creation of Carlyle Lake in 1967, flooding the snake’s habitat and leaving them in clustered a handful of suitable patches of land.

The team’s research suggests the snake has enough genetic diversity to rebound, though, Baker said, if recovery efforts are undertaken.

“As long as we don’t wait 20 to 30 years to make this a priority, they’ll recover more or less successfully,” she said. “If the habitat is there, it’s not too lake for the snakes.”

Header Image: While declining, eastern massasaugas rattlesnakes in Illinois show a lack of inbreeding. ©Michael Dreslik