Studying threatened desert turtles offers a new conservation strategy

In Nevada’s arid Ivanpah Valley, just southeast of Las Vegas, a massive unintended animal conservation experiment has revealed an unexpected result.

From 1997 to 2014, the US Fish and Wildlife Service moved more than 9,100 Mojave Desert turtles to the 100-square-kilometer (approximately 39 square miles) large-scale translocation site. The newcomers, many of whom were abandoned pets or had been displaced due to development, joined nearly 1,500 desert tortoises that already lived there.

Conventional wisdom would suggest that turtles from areas closest to the translocation site would fare better. But a new UCLA study, published today in Science, found no connection between the turtles’ place of origin and their chances of survival. However, he found a much better predictor.

Turtles with many genetic variations were much more likely to survive after their relocation, said UCLA conservation ecologist Brad Shaffer, senior author of the study. Like most organisms, turtles have two copies of their entire genome, with one copy from each parent. The more these copies differ from each other, the greater the heterozygosity of the organism.

The researchers compared the relocated turtles that lived or died in the same amount of time after being moved to the site. They found that the survivors had on average 23% greater heterozygosity than those who died. Simply put, turtles with more genetic variations had higher survival rates.

“It is in contrast to what we know from other translocation studies, but many genetic variations have undoubtedly been the best predictor of whether a turtle lived or died,” said Shaffer, professor of ecology and evolutionary biology and director of UCLA. The Kretz Center for California Conservation Science. “The relocation of endangered plants and animals is increasingly needed to counter the effects of climate change, and this provides us with a new tool to increase survival rates.”

Although the relationship between heterozygosity and survival was well supported by the study, it’s unclear why greater genetic variation is linked to survival rates, said former UCLA postdoctoral scholar Peter Scott, lead author of the study.

“Potentially, individuals with greater heterozygosity have greater genomic flexibility,” said Scott, who is now an assistant professor at West Texas A&M University. “Turtles with more variations are likely to have a better chance of having one copy of a gene that works really well in stressful or new environments than those individuals with two identical copies that only work really well in their home environment.”

The researchers wanted to make turtle conservation efforts more effective and uncover trends that would help other species as well, Scott said.

“Often, the chances of success for plant or animal relocation are pretty slim,” he said. “We wanted to understand why and use this understanding to increase survival.”

Over the years, turtles that had been abandoned as pets or removed from places like suburban Las Vegas developments and solar farms in the desert have been handed over to the U.S. Fishing and Wildlife Service.

The agency took blood samples for disease screening and tagged each animal before releasing them at the Ivanpah Valley site, which made it possible to trace the animals in subsequent investigations. UCLA researchers sequenced blood samples from 79 turtles that were released at the site and were known to be alive in 2015, and from another 87 known to have died after being released at the site.

Although the large-scale translocation site provided an intriguing dataset, it’s not the same as a controlled experiment. More studies would be needed to understand why more heterozygous tortoises have a higher chance of survival and precisely how much an increase in genetic variation improves a tortoise’s chances of survival.

“The only reason we could do this study was because the US Fish and Wildlife Service was incredibly forward-thinking when they created the translocation site and tracked down who lived and died,” Shaffer said. “Many died and no one was happy. But we can learn a lot from that unfortunate result to help conservation management improve.

“When we think of moving animals or plants out of danger or of repopulating an area emptied by a fire, we can now easily and economically measure genetic variability to better assess the probability of survival of those relocated individuals. It is not the only criterion, but it’s an important piece of the puzzle. ”