Inbreeding Threatens Michigan’s Only Rattlesnake — What It Means for Conservation

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Quick Shot

• MichiganOnly rattlesnake eastern massasauga species show evidence of this consanguineous depression.

• In two populations of eastern massasaugas, individuals with more inbreeding had lower reproductive output And survival.

• Measures restoration of genetic fitness These populations may be needed to prevent local extinctions.

• Care natural environment corridors Dispersal may also benefit other snake species that may be susceptible to inbreeding depression.

If you encounter a rattlesnake in Michigan, it’s an eastern massasauga (Sistrurus catenatus), the only venomous snake in the state. They are relatively small for rattlers, averaging two to three meters long like adults. You’ll be lucky to spot one, as eastern massasaugas spend most of their time hiding under logs or bushes near wetland habitats and tend to flee when disturbed. So, although massasaugas have a poisonous bite, humans are rarely bitten.

Although they have a geographically wide distribution across several U.S. states, from Michigan to Missouri, populations of eastern massasaugas have declined rapidly since the mid-1970s, according to tracking by the U.S. Fish and Wildlife Service. Them Listed as threat Under the Endangered Species Act in 2016, reasons for their decline in numbers due to illegal harvesting and fragmentation of habitat over the past 200 years include:

As the development of roads and human settlements progressed, eastern massasaugas became increasingly confined to smaller patches of habitat. One last articleConservation biologists have found that habitat fragmentation makes it difficult for massasaugas to reproduce successfully, thus reducing their chances of future survival.

Biologists from Michigan State University used genetics to trace the family history of snakes in two populations. By partnering with long-term monitoring projects led by Grand Valley State University, West Virginia University, and the Association of Zoos and Aquariums, the researchers were able to obtain DNA samples from more than 1,000 individual snakes captured and released in a project funded by the U.S. Fish and Wildlife Service.

Each captured snake was weighed, measured, assessed for sex and reproductive status, blood sampled, and then released with a unique PIT tag for individual identification. DNA taken from the blood sample served to create family trees for populations showing relatedness between individuals. Over 15 years, visits to the two populations have yielded estimates of snake births and snake deaths.

“This long-term field monitoring is the backbone of the study,” said Meaghan Clark, lead author and then-graduate student. Press release. “All of this was made possible by the fact that people caught these snakes in all seasons.”

Data analysis showed that massasauga inbreeding led to reproductive problems in these two populations. These massasaugas mated non-randomly with more closely related snakes, reducing their chances of producing viable offspring. Inbreeding reduces fitness by increasing the expression of deleterious gene combinations. The offspring of inbred massasaugas were 3.5 percent less likely to survive, and their annual survival rate was 11.6 percent lower. So why would these eastern massasaugas choose to mate with their relatives?

“Habitat loss and fragmentation prevent occasional migrations among eastern massasauga populations, increasing relatedness within each population over time,” lead author Clark explains via email. Additionally, massasaugas naturally tend to disperse short distances from their parents, limiting gene flow from their natal populations. “In our data set, we found that the distance between snakes and their parents was less than the distance between unrelated pairs of individuals,” Clark adds.

Therefore, already homegrown Michigan massasaugas are being squeezed ever closer to their relatives due to habitat change and loss. Genetic relatedness of the parents causes “inbreeding depression,” known declines in fitness and survival. Over time, you would expect inbreeding depression to reduce the Michigan massasauga population, leading to more breeding with close relatives.

Other eastern massasauga populations are generally even smaller, and their movements are similarly restricted by roads, farms, and other obstacles. This was the first study to directly measure the impact of inbreeding resulting from habitat fragmentation on the fitness of eastern massasaugas.

“These are fairly large and stable populations of Eastern Massasaugas,” said senior author Sarah Fitzpatrick. Press release. “Given that many other populations in the Midwest are much smaller and even more fragmented, it is concerning that we are detecting problems resulting from inbreeding in these populations.”

When a population of organisms becomes smaller and isolated, the chance of local extinction increases dramatically. A single natural event could wipe out these massasauga populations, which lack the nearby nutrient population buffer to replenish both genetic diversity and individuals.

“The way to counter this decline is to increase population size and facilitate gene flow with other populations,” says Clark. [of massasaugas]. Research is currently underway on how best to do this.” Saving genetic diversity to limit harmful gene combinations could be key to preserving Michigan populations of eastern massasaugas and even warrant the migration of snakes from other populations.

The study’s authors also recommend long-term monitoring of other snake populations to understand whether they successfully maintain their gene pools in the face of environmental changes that limit habitat connectivity. Implementing changes such as building underpasses for snakes to cross roads or creating openings in fences can improve connectivity and therefore increase gene flow between populations.

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