Integrative Zoology 2007; 2: 111-119
doi: 10.1111/j.1749-4877.2007.00050.x
ORIGINAL ARTICLE
Who killed Porthos? Genetic tracking of a gorilla death Kathryn J. JEFFERY,1 Kate A. ABERNETHY,2,3 Caroline E. G. TUTIN,2,3 Nicola A. ANTHONY1* and Michael W. BRUFORD1 1
Cardiff School of Biosciences, Cardiff University, UK, 2Centre International de Recherches Médicales, Franceville, Gabon, and Department of Biological and Molecular Sciences, University of Stirling, Stirling, UK
3
Abstract 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. Key words: ape, conservation, genetic tracking, non-invasive, microsatellite, western lowland gorilla.
INTRODUCTION The potential of genetic studies to add value to the interpretation of ape social systems has been much heralded in the last decade, despite the fact that analytical weaknesses associated with “non-invasive” sampling methods have hampered their successful application (Taberlet et al. 1999; Vigilant et al. 2001). While “classic” studies of population genetics and molecular ecology have now been carried out on gorillas at several sites in Western Equatorial Africa (WEA; e.g. Bradley et al. 2004; Clifford et al. 2004), few have previously tackled individual life history questions, which are key to under-
Correspondence: Kathryn J. Jeffery, Department of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK. Email:
[email protected] *Present address: Department of Biological Sciences, University of New Orleans, New Orleans, Louisiana, USA.
©
2007 ISZS, Blackwell Publishing and IOZ/CAS
standing contact and transfer rates, spatio-temporal movements and ultimately population social structure. Life-history data based on direct observations at forest clearings (“bais”) have become increasingly available in recent years (Magliocca et al. 1999; Parnell 2002; Stokes et al. 2003; Gatti et al. 2004; Magliocca & Gautier-Hion 2004; Robbins et al. 2004; Stokes 2004; Levrero et al. 2006). Although such studies have provided a wealth of valuable data on western gorilla social systems, bais are unique habitats that create a very different social landscape to that experienced by gorillas in the forest, and provide an unrepresentative “snapshot” of gorilla life, as even bai-frequenting groups spend 99% of their time in forested habitat (Parnell 2002). Detailed comparative observational data from forest sites are still relatively rare, due to visibility problems in thick understory and difficulties encountered with habituation, although in recent years Cipoletta (2003, 2004), Doran-Sheehy et al. (2004) and Bermejo (2004) have provided such data. In the present study, we demonstrate a novel applica-
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tion of molecular genetics for tackling specific questions of individual gorilla behavior, by tracing a female gorilla’s movements following the death of her silverback male, and implicating an adult male in the death of this silverback. We studied a group of western lowland gorillas at the Lopé National Park, Gabon between 1983 and 1993 using standard field tracking methods that depend on indirect evidence (especially analysis of night nests) combined with opportunistic observations (Tutin 1996). In 1993 the group’s silverback (Porthos) died following a fight with an unknown male gorilla, resulting in the immediate breakdown of his social group and disappearance of all surviving members (three young males and an adult female). In the absence of observational data, we used non-invasive genetic techniques to establish, post-hoc, the movements of individuals from Porthos’s group after his death.
MATERIALS AND METHODS
death to be infected bite- wounds inflicted by canines that conformed to the dimensions of another silverback male gorilla. His advanced age (estimated to be at least 45 years) was also apparent from the extent of tooth wear and skeletal decalcification. On 21 June 1993, the remains of a second, unidentified silverback (posthumously named “Yorick”) were discovered approximately six days post mortem, badly decomposed and partially eaten by a leopard, although the cause of death could not be determined. Tooth-wear and skull thinning revealed him to be elderly, although younger than Porthos. Shed hairs were collected from vacated night nests situated within a 50 km2 area of tropical lowland forest in the Lopé National Park, central Gabon (0°10' S, 11°35' E) between 1990 and 1999. Hairs were also plucked from the corpses of Porthos and Yorick, and one snag of hair was collected from a tree branch. Samples were collected with sterile tweezers and stored desiccated in paper envelopes at room temperature for up to 11 years before analysis.
Field Porthos’s social group was monitored between 1983 and 1993 using standard field tracking and observational techniques (Tutin 1996). As the study progressed it became clear that group size was declining: both maturing offspring and breeding females gradually began to disperse away from the group, yet there was no immigration. Although four offspring were born between 1985 and 1992, only two survived. By early 1993 Porthos himself was physically deteriorating and showed visible signs of ageing: group membership at this point comprised one adult female (“Madame Bovary”), and three young males (“Ignace,” “Sapho,” and “Papillon”), aged between 6 and 10 years (Table 1). On 22 April 1993, Porthos died; his corpse was recovered and autopsy revealed the cause of
Molecular Hairs with suitable roots were preselected for analysis (both plucked hairs and shed hairs from nests
