Restoring genetic diversity to isolated populations

The strength of a species lies in its genetic diversity.

However, when the number of plants or animals with physical access to one another decreases, inbreeding can decrease genetic diversity and therefore the species’ ability to reproduce and survive, according to South Dakota State University professor Michele Dudash, head of the Department of Natural Resource Management.

She and SDSU biology professor Charles Fenster are among an international group of eight scientists who support genetically managing fragmented plant and animal populations by bringing in individuals from other populations to maintain genetic diversity.

The group has published the conservation biology textbook “Genetic Management of Fragmented Animal and Plant Populations” in 2017 and, most recently, a guidebook for land managers, “A Practical Guide for Genetic Management of Fragmented Animal and Plant Populations.”

“This is a paradigm shift to actively manage populations to allow them to stay on the landscape,” said Dudash, a population biologist. She conducted the first study that showed the negative impact of inbreeding in wild plant populations. Through inbreeding, recessive traits that cause disease and otherwise weaken the individuals are more likely to appear in the population.

Land managers have been concerned about the potential negative effects of bringing individuals from one population physically separated to another population, Dudash noted. However, Fenster, whose expertise is in outbreeding depression, said his work has demonstrated that any ill effects tend to go away in future generations.

Increasing species viability

Plant breeders have produced high-yielding corn and other crops, for instance, by crossing unrelated varieties to produce a hybrid with the desired qualities, Fenster pointed out. Similar approaches have been successfully applied to wild populations.

For example, the Greater Prairie Chicken was once widespread in Illinois, but by the 1990s, it had been reduced to two isolated populations with decreasing fertility rates, Fenster said. The Illinois Department of Natural Resources rescued the dwindling populations by bringing in prairie chickens from Minnesota, Kansas and Nebraska. “Offspring increased and the populations became viable again,” he said.

In another case, female panthers from Texas were introduced to a declining population of Florida panthers, which was suffering the effects of inbreeding, leading to genetic rescue through the production of vigorous offspring.

The authors designed the guide to assist regional and county individuals managing these areas and species, Fenster explained. “It does not leave it up to the manager to sift through the literature, but provides clear decision trees and gives advice to pointed questions.”

This guidebook also helps land managers determine how many individuals need to be introduced into a population while maintaining the organism’s integrity, Dudash noted.

“We are saying if these populations are the same species with the same number of chromosomes, have been in contact with each other historically and live in the same general area, it is worth a try to bring them together,” she explained.

Impacting world

The landscape worldwide has changed dramatically in the last 500 years as nearly 70% of the global landscape has been impacted by humans, Fenster said. For example, crossing a large, cultivated field may make a species vulnerable to predators. Dams are important barriers for fish population. Therefore, managing the genetic diversity of these isolated populations is essential to their survival.

“Species need to be able to evolve in response to changes in climate and habitat and are doomed without genetic diversity,” Dudash said.