Habitat preservation isn’t always viable, but introducing genetic diversity might keep threatened species viable, scientists find
Nearly 23,000 of the world’s known plant and animal species were found to be threatened with extinction in 2015, including 37 percent of mammals and 14 percent of birds assessed by the International Union for Conservation of Nature’s Red List of Threatened Species. The go-to-strategy for rescuing them has long been to set aside tracts of healthy land in which the animals could spread out and migration corridors that allow them to mix with other populations, gaining resilience via a broadened gene pool.
But climate change and human sprawl have made that approach difficult, prompting biologists to explore new tools—including importing migrants—to usher shrinking populations back to health on the habitat they’ve got.
A new study by biologists Brett Melbourne and Ruth Hufbauer, enlisting the help of an army of tiny flour beetles, offers encouraging insight into how well that might work.
“Our research suggests that introducing as little as one individual from a different genetic background can have a really big impact,” Melbourne says.
For a decade, Melbourne, an assistant professor in the Department of Ecology and Evolutionary Biology at the University of Colorado Boulder, has been usingTribolium castaneum beetles housed in small, clear plastic boxes as models of species on the brink.
They don’t eat much or take up much space, and their generation lasts only one month, so they’re ideal for studying what happens to species when small things start to change in their habitat.
In the wild, Melbourne explains, habitat loss can send a species on the road to extinction. But when the population gets small enough, it is a series of “random events”—like a female mammal getting hit by a car or contracting a virus—that does it in. “The question now is: How does a population respond to environmental changes, and what can we do to help them adapt and protect them against those random processes?”
Together with Ruth Hufbauer, an evolutionary ecologist with Colorado State University, Melbourne recently published a study in the prestigious Proceedings of the National Academy of Sciences, comparing two emerging conservation methods: “demographic rescue,” in which several genetically similar individuals are brought in to bolster the population; and “genetic rescue” in which just a few genetically different individuals are imported.
If in doubt, get some new genes in there.”
In an experiment conducted at Colorado State University, they filled 244 boxes with wheat flour and added 50 or 150 beetles. After letting them thrive for a few generations, they swapped out the wheat for corn – a change akin to a shift in available food in the wild. As expected, populations plummeted. Then, researchers either left them alone, added 11-33 more beetles to their box, added 1-3 beetles from a different lineage, or did both.
The results were surprising. By the end of six generations, about half the populations left to fend for themselves were extinct (remarkably, some adapted and rebounded with no help). Adding several new members helped the larger populations grow long-term, but had less impact on the small ones. Rather than adding many new members, adding 1-3 genetically different individuals was by far the most potent approach, by boosting the fitness of the population and ultimately increasing the number of members through new births as the population became better adapted.
Hufbauer explains that for many threatened species, isolation leads to inbreeding, making those left less fit to deal with change. Bringing in someone new can introduce new, beneficial genetic variations. “If in doubt, get some new genes in there,” says Hufbauer.
Take, for example, the Florida panther. In the mid-1990s, populations were declining and inbreeding was rampant. Hoping to reverse the trend, wildlife managers made a controversial move, introducing eight females from Texas. By 2003, the population had tripled.
She cautions that “genetic rescue” isn’t always ideal. Certain species are so unique wildlife managers want to preserve that uniqueness. That’s why it’s good to know, from this study and others, that demographic rescue works too.
Melbourne continues to use the beetles to study how species adapt or fail to adapt to changing habitats. Now, he is conducting new experiments to see how populations can be rescued from extinction due to climate change using such strategies such as assisted migration.
“These results don’t necessarily apply in a blanket way to all species, but they are definitely promising,” he says.
Lisa Marshall (Jour, PolSci’94) is a freelance writer who lives near Estes Park.