Chimpanzee (Pan troglodytes schweinfurthii) Population Spans Multiple Protected Areas in the Albertine Rift

Abstract

We used mitochondrial DNA to examine gene flow in a region of western Uganda that has received little attention regarding chimpanzee population dynamics. The area is critical to gene flow between isolated Democratic Republic of Congo populations and the rest of East Africa. None of the chimpanzees in each of the 4 protected areas under consideration (Toro-Semliki Wildlife Reserve, Semuliki National Park, Rwenzori Mountains National Park and Itwara Central Forest Reserve) are fully habituated. Therefore, it is not clear whether one or more populations have historically used this fragmented landscape for (1) regular ranging and/or (2) infrequent dispersal. We incorporated the published sequences of the first hypervariable region of the D-loop of the mitochondrial genome from 3 previously sampled sites (<i>n</i> = 39) while also contributing the first extensive genetic sampling of chimpanzees in Toro-Semliki (<i>n</i> = 80). Our goal was to generate a historical baseline model of metapopulation dynamics in this region and determine which, if any, of these protected areas forms a fragmented landscape for a single chimpanzee population. According to a discriminant analysis of principal components, the haplotypes at Toro-Semliki form a central cluster, and Itwara is its nearest genetic neighbor. Rwenzori Mountains National Park is the most distant neighbor of all protected areas. We performed an analysis of molecular variance for 14 different population models that divided the samples from the 4 protected areas into 2, 3 or 4 populations. The best fit model included 3 populations: Toro-Semliki Wildlife Reserve and Itwara Forest Reserve comprised a single population; Semuliki National Park and Rwenzori Mountains National Park formed 2 additional separate populations (variance among = 9%, <i>p</i> = 0.014). The results indicated that some protected areas comprised distinctive populations, while others formed a fragmented landscape for a population’s ranging for foraging purposes. Therefore, the edges of a protected area do not always define a chimpanzee population. We propose a closer examination of those dynamics through renewed sampling. Advances in DNA extraction and next-generation sequencing will allow us to compare thousands of single nucleotide polymorphisms in the genomes of unhabituated chimpanzees living in each of these protected areas.