The role of Pleistocene refugia and rivers in shaping gorilla genetic diversity in central Africa.

The role of Pleistocene forest refugia and rivers in the evolutionary diversification of tropical biota has been the subject of considerable debate. A range-wide analysis of gorilla mitochondrial and nuclear variation was used to test the potential role of both refugia and rivers in shaping genetic diversity in current populations. Results reveal strong patterns of regional differentiation that are consistent with refugial hypotheses for central Africa. Four major mitochondrial haplogroups are evident with the greatest divergence between eastern (A, B) and western (C, D) gorillas. Coalescent simulations reject a model of recent east-west separation during the last glacial maximum but are consistent with a divergence time within the Pleistocene. Microsatellite data also support a similar regional pattern of population genetic structure. Signatures of demographic expansion were detected in eastern lowland (B) and Gabon/Congo (D3) mitochondrial haplogroups and are consistent with a history of postglacial expansion from formerly isolated refugia. Although most mitochondrial haplogroups are regionally defined, limited admixture is evident between neighboring haplogroups. Mantel tests reveal a significant isolation-by-distance effect among western lowland gorilla populations. However, mitochondrial genetic distances also correlate with the distance required to circumnavigate intervening rivers, indicating a possible role for rivers in partitioning gorilla genetic diversity. Comparative data are needed to evaluate the importance of both mechanisms of vicariance in other African rainforest taxa.

Ten days in the life of a mandrill horde in the Lopé Reserve, Gabon.

Mandrills have long been known to form large aggregations in the wild, but it has proved difficult to obtain detailed information on the socioecology of these groups. An unusually large (>600) horde of mandrills was followed for ten days during the 1995 dry season in Central Gabon, and data were collected on group composition and ecology while the mandrills were in an area of forest-savanna mosaic habitat in the north of the Lopé Reserve. Three separate counts of most of the group showed that fully coloured "fatted" adult males were present throughout the horde at a mean ratio to other individuals of 1:21. Paler "non-fatted" adult and sub-adult males were also distributed throughout. Mandrill diet over the ten days consisted mainly of insects, seeds from forest trees, and leaves or stems of understory herbaceous plants. Feeding was extremely selective, with most food items consumed in a much higher proportion than would be predicted from their relative availability. Ranging data also showed that the mandrills foraged preferentially in certain forest types within the forest-savanna mosaic, namely in Marantaceae and Rocky Forest. It is suggested that one reason why mandrills pass through gallery forests and forest-savanna mosaic in the dry season in the Lopé Reserve is because they find fruit there from preferred species, which are no longer fruiting in the main forest block, thus allowing them to maintain the fruit component of their diet at a time of fruit shortage. © 1996 Wiley-Liss, Inc.

Who killed Porthos? Genetic tracking of a gorilla death.

We describe a novel application of "forensic" genetics to study a key demographic event in a population of wild gorillas. We used microsatellite genotyping and non-invasively collected DNA samples to identify one individual western lowland gorilla as being most likely to have caused the death of another in Lopé National Park, Gabon. Data from relatively few genotypes permitted the identification of female transfer events and the interpretation of individual behavior that was previously impossible using observational methods, thus providing rare behavioral data on an elusive forest-dwelling species. Importantly, this study highlights the need for future studies of dispersal and local population structuring in forest populations, and more accurate population census methods. Genetic studies focusing on individual identification may play a valuable role in future gorilla conservation efforts.

Distinguishing gorilla mitochondrial sequences from nuclear integrations and PCR recombinants: guidelines for their diagnosis in complex sequence databases.

Nuclear integrations of mitochondrial DNA (Numts) are widespread in many taxa and if left undetected can confound phylogeny interpretation and bias estimates of mitochondrial DNA (mtDNA) diversity. This is particularly true in gorillas, where recent studies suggest multiple integrations of the first hypervariable (HV1) domain of the mitochondrial control region. Problems can also arise through the inadvertent incorporation of artifacts produced by in vitro recombination between sequence types during polymerase chain reaction amplification. This issue has attracted little attention yet could potentially exacerbate errors in databases already contaminated by Numts. Using a set of existing diagnostic tools, this study set out to systematically inventory Numts and PCR recombinants in a gorilla HV1 sequence database and address the degree to which existing public databases are contaminated. Phylogenetic analysis revealed three distinct gorilla HV1 Numt groups (I, II, and III) that could be readily differentiated from mtDNA sequences by Numt-specific diagnostic sites and sequence-based motifs. Several instances of genuine recombination were also identified by a suite of detection methods. The location of putative breakpoints was identified by eye and by likelihood analysis. Findings from this study reveal widespread nuclear contamination of gorilla HV1 GenBank databases and underline the importance of recognizing not only Numts but also PCR recombinant artifacts as potential sources of data contamination. Guidelines for the routine identification of Numts and in vitro recombinants are presented and should prove useful in the detection of similar artifacts in other species mtDNA databases.

Mitochondrial DNA phylogeography of western lowland gorillas (Gorilla gorilla gorilla).

The geographical distribution of genetic variation within western lowland gorillas (Gorilla gorilla gorilla) was examined to clarify the population genetic structure and recent evolutionary history of this group. DNA was amplified from shed hair collected from sites across the range of the three traditionally recognized gorilla subspecies: western lowland (G. g. gorilla), eastern lowland (G. g. graueri) and mountain (G. g. beringei) gorillas. Nucleotide sequence variation was examined in the first hypervariable domain of the mitochondrial control region and was much higher in western lowland gorillas than in either of the other two subspecies. In addition to recapitulating the major evolutionary split between eastern and western lowland gorillas, phylogenetic analysis indicates a phylogeographical division within western lowland gorillas, one haplogroup comprising gorilla populations from eastern Nigeria through to southeast Cameroon and a second comprising all other western lowland gorillas. Within this second haplogroup, haplotypes appear to be partitioned geographically into three subgroups: (i) Equatorial Guinea, (ii) Central African Republic, and (iii) Gabon and adjacent Congo. There is also evidence of limited haplotype admixture in northeastern Gabon and southeast Cameroon. The phylogeographical patterns are broadly consistent with those predicted by current Pleistocene refuge hypotheses for the region and suggest that historical events have played an important role in shaping the population structure of this subspecies.

Catastrophic ape decline in western equatorial Africa.

Because rapidly expanding human populations have devastated gorilla (Gorilla gorilla) and common chimpanzee (Pan troglodytes) habitats in East and West Africa, the relatively intact forests of western equatorial Africa have been viewed as the last stronghold of African apes. Gabon and the Republic of Congo alone are thought to hold roughly 80% of the world's gorillas and most of the common chimpanzees. Here we present survey results conservatively indicating that ape populations in Gabon declined by more than half between 1983 and 2000. The primary cause of the decline in ape numbers during this period was commercial hunting, facilitated by the rapid expansion of mechanized logging. Furthermore, Ebola haemorrhagic fever is currently spreading through ape populations in Gabon and Congo and now rivals hunting as a threat to apes. Gorillas and common chimpanzees should be elevated immediately to 'critically endangered' status. Without aggressive investments in law enforcement, protected area management and Ebola prevention, the next decade will see our closest relatives pushed to the brink of extinction.