Inbreeding - It's the New Frontier!

When you hear about inbreeding, you probably think about the same things that I do: poor genetic diversity, low survivability, a plethora of deleterious alleles, and August: Osage County. Inbreeding in populations is usually a bad thing, because it decreases the overall heterozygosity of a population, reducing the variance in alleles, and often allows for the expression of bad alleles that have been silently accumulating in a population, but haven’t shown up yet (An example of this in humans would be cystic fibrosis, which is carried by 1 out of every 25 individuals, but expressed in only 1/3000 individuals). If a mother is heterozygous for a deleterious allele, and she passes it on to half of her offspring, and then her offspring breed with each other, the chances of their children expressing this allele are much higher than if random breeding were to occur. 

In the short term, inbreeding can be a very bad thing for a population; however, it can actually be a good thing for a population in the long term. Crazy you say? A little. But the tendency of inbred individuals to more frequently express bad alleles can work in the favor of a population – these alleles can be purged out of the population, and actually reduce the amount of carriers in the long term. This exact phenomenon has been observed in a population of Mountain Gorillas in an article published in Science this week.

Gorilla beringei beringei, the
Mountain Gorilla

Habitat loss is a problem for any species, but the population of gorillas that were studied for this paper faced this to the extreme. In 1981, this population fell to about 253 total individuals. Thanks to recent conservation efforts, their numbers have risen to a paltry 480 individuals. Unfortunately, any time a population experiences a large loss in numbers (called a bottleneck), the population’s genetic diversity plummets, and the inbreeding coefficient (which is a number used to measure the observed heterozygosity) increases.  When this population of gorillas was analyzed, scientists found that they were two to three times less diverse than other populations of gorillas in other parts of the world.

Scientists are worried that this lack of genetic diversity could make the population of gorillas more susceptible to diseases and environmental changes, they have also found that the gorillas in this population have fewer harmful loss of function gene variants.

By looking a little deeper into each genome, researchers also found that this kind of inbreeding wasn’t uncommon – mountain gorillas have survived in small numbers for thousands of years, suggesting that the population has been in the hundreds for much longer than humans could have intervened. This is promising for the gorilla population, but small numbers mean that this population is still at a reasonably high risk for extinction.

While the gorilla population is currently on the rise, conservation efforts are now more important than ever. We don’t want to lose any more species than we have to, and hopefully our newfound, deeper understanding of this one will help it exist for years to come.

~David Almanzar (Group A)