Ebola hemorrhagic fever kills up to 90% of infected humans,
typically by organ failure or blood loss (dehydration).
The causative virus is also deadly to nonhuman primates;
outbreaks have killed so many Western lowland gorillas
this past decade that they're now classified as
critically endangered.
It's unclear how mass mortality will affect long-term survival of the gorilla population. It's possible that it will either reduce or enhance their genetic fitness.
Widespread declines in the gorilla population may facilitate inbreeding (reducing genetic fitness) as well as immigration (enhancing genetic fitness). Understanding which effect is likely to prevail will help gorilla conservation efforts.
Pascaline Le Gouar (CNRS, France) and coworkers have undertaken a study aimed at this goal. Their research suggests that the genetic diversity of Western lowland gorillas remains adequate for long-term survival of the species, as long as gorilla numbers begin to rebound.
Gorilla genetics.
The scientists studied three populations of western lowland gorillas in the Republic of Congo, both before and after Ebola outbreaks. Two were exposed to the virus (once or twice this past decade), and one was not.
The outbreaks killed over 90% of the gorillas. DNA from fecal samples was extracted and stored for later analysis.
Rare genetic variations were still present in the gorilla populations both before and after Ebola outbreaks (suggesting retention of genetic diversity). The scientists propose two possible explanations.
One explanation is that genetically-similar gorillas took the place of the recently deceased gorillas. Another is that the gorilla population wasn't reduced enough (or the time after the viral outbreak wasn't long enough) to detect changes in gorilla genetics.
The number of gorillas remaining and the populational rebound after the decline are the most important determinants of genetic diversity after a spout of high mortality. This suggests that gorilla numbers need to recover quickly if the overall population is to withstand these recent Ebola outbreaks.
The scientists found that one of the gorilla populations had a different genetic composition after Ebola, and the other did not. This suggests that the virus may be killing certain gorillas in preference to others.
The scientists propose that social gorillas may have been killed off faster than others, which may be expected, because the virus is transmitted by direct contact with infected individuals. It's possible that selective pressure against social behavior may fundamentally change gorilla society in the long term.
Implications.
Long-term studies of this type are needed for scientists to preserve the remaining Western lowland gorillas, and possibly to gain insight into the the long-term consequences of high mortality on gorilla social behavior. This research also has implications for human health following large-scale mortality, although one may hope that such an event is not on the horizon.
for more information:
Le Gouar, P. J., Vallet, D., David, L., Bermejo, M., Gatti, S., Levréro, F., Petit, E. J., & Ménard, N. (2009). How Ebola Impacts Genetics of Western Lowland Gorilla Populations PLoS ONE, 4 (12) DOI: 10.1371/journal.pone.0008375