The geographic distribution of genetic diversity within gorillas

Abstract

Gorillas, like all non-human great apes, are endangered. Understanding the distribution of genetic diversity across their range is important because low diversity may arise in small populations through increased inbreeding, and, by reducing reproductive fitness, may lead to decreased chances of persistence of a given population. Previous studies found higher genetic diversity in the western (Gorilla gorilla) than in the eastern gorillas (Gorilla beringei), but rarely employed individuals of known geographic origin to investigate the distribution of diversity across multiple populations. The present study fills that gap by analyzing 1,161 individuals from nine sites across all four currently recognized Gorilla subspecies. Genetic diversity at each site was estimated using published data from seven highly-variable microsatellite loci. We found that the small and fragmented populations of Cross River gorillas, eastern lowland gorillas and mountain gorillas were less diverse than any of the five analyzed western lowland gorilla populations. The higher levels of genetic variation within the western lowland gorillas might be best explained by the facts that they (i) exhibit larger present and past effective population sizes than the other subspecies and (ii) maintain higher rates of gene flow through the existence of largely continuous habitat within their range. With regard to conservation, the high genetic diversity within western lowland gorillas is encouraging and retention of dispersal corridors between already protected areas is essential. Am. J. Primatol. 77:974-985, 2015. © 2015 Wiley Periodicals, Inc.

Population‐level assessment of genetic diversity and habitat fragmentation in critically endangered Grauer's gorillas

“…The relative levels of genetic diversity among gorilla taxa obtained in our study (highest in western lowland gorillas, followed by Grauer's and finally mountain gorillas) are in line with previous work (Fünfstück & Vigilant, ; Prado‐Martinez et al, ; Xue et al, ), despite our small sample sizes and inclusion of relatives. Furthermore, although we used microsatellite loci originally developed in western lowland gorillas (Bradley, Boesch, & Vigilant, ), which may lead to erroneous inferences in cross‐species comparisons (Lachance & Tishkoff, ; Rogers & Jorde, ), our results are consistent with studies that relied on whole genome and mitochondrial sequencing data, which are free of ascertainment bias (Prado‐Martinez et al, ; Xue et al, ; van der Valk et al, in review).…”

“…Furthermore, although we used microsatellite loci originally developed in western lowland gorillas (Bradley, Boesch, & Vigilant, ), which may lead to erroneous inferences in cross‐species comparisons (Lachance & Tishkoff, ; Rogers & Jorde, ), our results are consistent with studies that relied on whole genome and mitochondrial sequencing data, which are free of ascertainment bias (Prado‐Martinez et al, ; Xue et al, ; van der Valk et al, in review). The observed differences among gorilla taxa have been suggested to reflect differences in current effective and census population sizes and are the result of continuous, long‐term population decline, limited current distribution range and fragmented nature of the eastern gorilla habitat (Fünfstück & Vigilant, ; Plumptre et al, ; Roy et al, a; Xue et al, ). Among eastern gorillas, Grauer's gorillas tend to show higher values of genetic diversity than mountain gorillas, but the difference is not significant (this study and Fünfstück and Vigilant ()).…”

“…The observed differences among gorilla taxa have been suggested to reflect differences in current effective and census population sizes and are the result of continuous, long‐term population decline, limited current distribution range and fragmented nature of the eastern gorilla habitat (Fünfstück & Vigilant, ; Plumptre et al, ; Roy et al, a; Xue et al, ). Among eastern gorillas, Grauer's gorillas tend to show higher values of genetic diversity than mountain gorillas, but the difference is not significant (this study and Fünfstück and Vigilant ()). In mountain gorillas, the Bwindi population is generally more genetically diverse than the Virunga population, consistent with previous reports (Fünfstück & Vigilant, ).…”

“…All four gorilla subspecies are critically endangered (IUCN, ) through a combination of threats from bushmeat hunting, habitat loss and degradation, and spread of infectious disease (Bermejo et al, ; Caillaud et al, ; Junker et al, ). The four subspecies differ markedly in population and range sizes, levels of genetic diversity and extend of habitat fragmentation (Fünfstück & Vigilant, ), partly as result of biogeographic processes and partly as a consequence of recent anthropogenic activities (Bergl & Vigilant, ; Plumptre et al, ; Roy et al, a; Xue et al, ). Western lowland gorillas ( G. gorilla gorilla ) occupy the largest range of all gorilla taxa, inhabiting largely continuous habitat that allows for high rates of gene flow (Fünfstück & Vigilant, ; IUCN, ).…”

“…The four subspecies differ markedly in population and range sizes, levels of genetic diversity and extend of habitat fragmentation (Fünfstück & Vigilant, ), partly as result of biogeographic processes and partly as a consequence of recent anthropogenic activities (Bergl & Vigilant, ; Plumptre et al, ; Roy et al, a; Xue et al, ). Western lowland gorillas ( G. gorilla gorilla ) occupy the largest range of all gorilla taxa, inhabiting largely continuous habitat that allows for high rates of gene flow (Fünfstück & Vigilant, ; IUCN, ). They also have the largest census population size of all gorilla species, with an estimated 140,000 individuals (Williamson, Maisels, & Groves, ).…”