Its true the Eastern Lowland Gorillas Heading Towards 'Genetic Meltdown' (according to George Dvorsky of Conservation Grauer gorillas.)
From the Dian Fossey Gorilla Fund International Eastern lowland gorillas in the Democratic Republic of the Congo have endured dramatic population declines in recent decades, leading to a startling lack of genetic diversity and a slew of harmful mutations, according to new research.
By comparing the genomes of living eastern lowland gorillas, also known as Grauerâ€™s gorillas, with genomes derived from museum samples, researchers from the Swedish Museum of Natural History (SMNH) and Uppsala University have shown that genetic diversity is declining in the species, while inbreeding is increasing.
This double-whammy is due to declining populations, and itâ€™s causing an effect known as â€œtemporal genomic erosion,â€ whereby the lack of genetic diversity is introducing deleterious mutations in Grauerâ€™s gorillas, including fertility problems and a reduced capacity to ward off infectious diseases. The new research was published today in Current Biology. Advertisement, Needless to say, this is making an already bad situation for the Grauerâ€™s gorilla even worse.
But while the genetic diversity of these gorillas is plummeting, it has yet to reach the point of no returnâ€”a state known as â€œgenetic meltdown,â€ after which time there isnâ€™t enough diversity left in the gene pool for reproductive viability. Thereâ€™s still time to bring these apes back from the brink, we just need to act.
Museum samples of Grauerâ€™s gorilla skulls. Image: Katerina Guschanski Over the past two decades, the population of Grauerâ€™s gorillas in the Democratic Republic of the Congo has decreased by 80 percent. As a result of poaching and loss of habitat, there are less than 4,000 individuals alive today, and the species is listed as critically endangered.
To see if this population decline was mirrored by a loss of genetic diversity, the SMNH and Uppsala scientists behind the new study analyzed eastern gorilla genomes over the past century by studying samples kept at museums.
Itâ€™s the first study to use historical genomes from an endangered species to investigate changes in genomic variation through time.
We think there is great potential for this approach to be implemented on a much wider scale on endangered species in general,â€ Love DalÃ©n, a researcher at SMNH and a co-author of the new study, told Earther.
DalÃ©n and his colleagues sequenced 11 genomes from eastern gorillas dating back 100 years. The DNA of the archived specimens, which were extracted from teeth and dry-tissue samples, were badly degraded, but by applying the same methods that are normally used to restore even older samples, such as mammoths and Neanderthals, the scientists were able to recover good and reliable genetic data.
It would, of course, have been great if we could have sequenced even more museum specimens since this would have allowed for higher resolution,â€ DalÃ©n told Earther. â€œOverall, the finding of significant changes in Grauerâ€™s gorillas is robust in my opinion, since statistical significance takes into account the small sample size.â€ Advertisement A juvenile Grauerâ€™s gorilla.
Dian Fossey Gorilla Fund International Results confirmed a loss of genetic diversity among living Grauerâ€™s gorillas, of which DNA samples were taken from seven individuals.
Whatâ€™s more, an alarming batch of genetic mutations has crept in over the past four to five generationsâ€”mutations that are making these gorillas more susceptible to communicable and genetic diseases, and less capable of adapting to environmental changes. Many of these mutations are classified as â€œLoss of Functionâ€ (LoF), which, as the name suggests, happens when a gene loses its evolved function.
Over the last 100 years, Grauerâ€™s gorillas have acquired several LoF mutations which, in humans and other related species, are related to changes in immune responses and male fertility.
The researchers also detected genes associated with finger and toe development, which may explain why many living Grauerâ€™s gorillas have fused digits. Interestingly, the researchers also conducted a similar study of mountain gorillas, applying the same techniques.
No significant genetic changes were detected; these gorillas, a closely-related subspecies, appear to be sustaining their genetic diversity and reproductive viability despite recent population losses due to similar factors.
The reason for the observed increase in harmful mutations in Grauerâ€™s gorillas compared to mountain gorillas, said DalÃ©n, may have something to do with differences in their long-term history. Grauerâ€™s gorillas went through a major population increase several thousand years ago, while the population of mountain gorillas remained low for several thousands of years.
Somewhat counter-intuitively, the small population size of mountain gorillas could have allowed natural selection to weed out acquired deleterious mutations in a process known as genetic purging. By contrast, the population increase in Grauerâ€™s gorillas introduced a large number of mutationsâ€”including harmful ones.
Once the Grauerâ€™s gorilla started declining in recent decades, we think these low-frequency harmful mutations may have started increasing in frequency due to stochastic allele changesâ€”so-called genetic drift,â€ said DalÃ©n. Advertisement As the new study suggests, itâ€™s critical that we stop, and ideally reverse, the demographic decline in Grauerâ€™s gorilla. â€œThe smaller the population gets, the more harmful mutations are likely to increase even further in frequency.
This could lead to a negative feedback loop called a mutational meltdown. So the decline really needs to be stopped.â€ The action wonâ€™t be easy. The ongoing conflict in the DRC and the threat of Ebola has made conservation efforts difficult, if not impossible. Hopefully, sanity will reign, and weâ€™ll be able to implement meaningful efforts to preserve this remarkable group of animals.