Admixture between historically isolated mitochondrial lineages in captive Western gorillas: recommendations for future management

Abstract

Although captive populations of western gorilla have been maintained in the United States for over a century, little is known about the geographic origins and genetic composition of the current zoo population. Furthermore, although previous mitochondrial analyses have shown that free-range gorilla populations exhibit substantial regional differentiation, nothing is known of the extent to which this variation has been preserved in captive populations. To address these questions, we combined 379 pedigree records with data from 52 mitochondrial sequences to infer individual haplogroup affiliations, geographical origin of wild founders and instances of inter-breeding between haplogroups in the United States captive gorilla population. We show that the current captive population contains all major mitochondrial lineages found within wild western lowland gorillas. Levels of haplotype diversity are also comparable to those found in wild populations. However, the majority of captive gorilla matings have occurred between individuals with different haplogroup affiliations. Although restricting crosses to individuals within the same haplogroup would preserve the phylogeographic structure present in the wild, careful management of captive populations is required to minimize the risk of drift and inbreeding. However, when captive animals are released back into the wild, we recommend that efforts should be made to preserve natural phylogeographic structure.

Keywords: Captive gorillas; Conservation; Great apes; Mitochondrial diversity.

Figure 1.

Frequencies and geographic distribution of major gorilla mitochondrial haplogroups across Central Africa. Color/texture patterns and circle areas represent the geographic distribution of different haplogroups and relative sample sizes respectively, using data (modified) from (Anthony et al. (2007a).

Figure 2.

Bayesian phylogenetic tree of the first hyper-variable region (HVI) from 197 reference gorillas (Gorilla gorilla and G. beringei) and 52 gorillas (G. gorilla) captive in US zoos. Haplogroups A (G. beringei beringei) and B (G. b. graueri) were used to root the tree. Numbers indicate the posterior probability support for a given branch in the tree and bullets (∙) represent captive gorilla sequences.

Figure 3.

Percentage of mitochondrial haplogroups in 39 wild founders and 228 captive gorillas in US zoos (Wilms 2010).