Too close for comfort. Sea lions suffer from more diseases if they’re inbred.

Inbreeding Breeds Infections

Animals that are more inbred are less healthy and more prone to suffer from infections, according to a new study of California sea lions. The finding suggests that conservationists will face an extra hurdle when protecting small, dwindling populations.

Studies have suggested that the more diverse the major histocompatability complex--a set of genes involved with the immune system--the less likely an organism is to fall prey to a pathogen. From lab experiments, biologists had some evidence that inbred animals were more likely to get sick. But data about the effect of inbreeding on disease in natural populations have been spotty.

Veterinarians at the Marine Mammal Center in Sausalito, California, took skin or blood samples from 371 stranded sea lions that were brought to the center. They sent the samples--along with a diagnosis of each animal's health problems--to veterinarian Karina Acevedo-Whitehouse of the University of Cambridge, U.K. Acevedo-Whitehouse extracted DNA from the samples and determined the degree of inbreeding from genetic markers called microsatellites. She compared animals with different types of health problems: cancer (which can be caused by viruses), bacterial and parasitic worm infections, toxic algal poisoning, and trauma, such as gunshot wounds.

Sea lions with cancer were most inbred, the researchers report in the 6 March issue of Nature, followed by those with other infectious diseases. Those suffering from trauma, which formed a control group, showed the lowest degree of inbreeding. More inbred animals also suffered from a greater variety of parasites in their gut, and they took longer to recover from diseases that couldn't be diagnosed. Acevedo-Whitehouse says inbred animals could act as reservoirs of disease in a population, helping pathogens spread.

The study demonstrates another reason why genetic diversity is important for wildlife, says Tim Caro, a conservation biologist at the University of California, Davis. That inbreeding causes juvenile mortality is “very old hat," Caro says, but the link between inbreeding and infectious diseases is new. Inbreeding could add to the costs of conservation programs, he says, because managers will have to deal with more disease.

Related sites
The dangers of inbreeding dogs, from the Canine Diversity Project
About inbreeding among cheetahs
The Marine Mammal Center