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Gilby I.C.,Arizona State University | Machanda Z.P.,Harvard University | Mjungu D.C.,The Jane Goodall Institute | Rosen J.,Harvard University | And 3 more authors.
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2015

Even when hunting in groups is mutually beneficial, it is unclear howcommunal hunts are initiated. If it is costly to be the only hunter, individuals should be reluctant to hunt unless others already are. We used 70 years of data from three communities to examine how male chimpanzees ‘solve’ this apparent collective action problem. The ‘impact hunter’ hypothesis proposes that group hunts are sometimes catalysed by certain individuals that hunt more readily than others. In two communities (Kasekela and Kanyawara), we identified a total of five males that exhibited high hunt participation rates for their age, and whose presence at an encounter with red colobus monkeys increased group hunting probability. Critically, these impact hunters were observed to hunt first more often than expected by chance. We argue that by hunting first, these males dilute prey defences and create opportunities for previously reluctant participants. This by-product mutualism can explain variation in group hunting rates within and between social groups. Hunting rates declined after the death of impact hunter FG in Kasekela and after impact hunter MS stopped hunting frequently in Kanyawara. There were no impact hunters in the third, smaller community (Mitumba), where, unlike the others, hunting probability increased with the number of females present at an encounter with prey. © 2015 The Author(s) Published by the Royal Society. All rights reserved. Source

Gilby I.C.,Duke University | Brent L.J.N.,Duke University | Wroblewski E.E.,Stanford University | Rudicell R.S.,University of Alabama at Birmingham | And 3 more authors.
Behavioral Ecology and Sociobiology | Year: 2013

Coalitionary aggression occurs when at least two individuals jointly direct aggression at one or more conspecific targets. Scientists have long argued that this common form of cooperation has positive fitness consequences. Nevertheless, despite evidence that social bond strength (which is thought to promote coalition formation) is correlated with fitness in primates, cetaceans, and ungulates, few studies have directly examined whether coalitionary aggression improves reproductive success. We tested the hypothesis that among free-ranging chimpanzees (Pan troglodytes schweinfurthii), participation in coalitionary aggression increases reproductive output. Using 14 years of genetic and behavioral data from Gombe National Park, Tanzania, we found that coalitionary aggression increased a male's chances of (A) siring offspring, compared to other males of similar dominance rank, and (B) ascending in rank, a correlate of future reproductive output. Because male chimpanzees form coalitions with many others within a complex network, we used social network analysis to identify the types of connections correlated with these fitness benefits. The beneficiaries of coalitionary aggression were males with the highest "betweenness"-that is, those who tended to have coalition partners who themselves did not form coalitions with each other. This suggests that beyond simply recognizing third-party relationships, chimpanzees may use this knowledge to choose coalition partners. If so, this is a significant step forward in our knowledge of the adaptive value of social intelligence. Regardless of mechanism, however, this is the first evidence of genetic benefits of coalitionary aggression in this species, and therefore has important implications for understanding the evolution of cooperation. © 2012 Springer-Verlag Berlin Heidelberg. Source

Lonsdorf E.V.,Franklin And Marshall College | Lonsdorf E.V.,Lester sher Center For The Study And Conservation Of Apes | Anderson K.E.,Lester sher Center For The Study And Conservation Of Apes | Stanton M.A.,George Washington University | And 5 more authors.
Animal Behaviour | Year: 2014

Sex differences in the behaviour of human children are a hotly debated and often controversial topic. However, several recent studies have documented a biological basis to key aspects of child social behaviour. To further explore the evolutionary basis of such differences, we investigated sex differences in sociability in wild chimpanzee, Pan troglodytes schweinfurthii, infants at Gombe National Park, Tanzania. We used a long-term data set on mother-infant behaviour to analyse the diversity of infant chimpanzee social partners from age 30 to 36 months. Male infants (N=12) interacted with significantly more individuals than female infants did (N=8), even when maternal sociability was controlled for. Furthermore, male infants interacted with significantly more adult males than female infants did. Our data indicate that the well-documented sex differences in adult chimpanzee social tendencies begin to appear quite early in development. Furthermore, these data suggest that the behavioural sex differences of human children are fundamentally rooted in our biological and evolutionary heritage. © 2013 The Association for the Study of Animal Behaviour. Source

Piel A.K.,University of California at San Diego | Piel A.K.,University of Cambridge | Stewart F.A.,University of Cambridge | Pintea L.,The Jane Goodall Institute | And 8 more authors.
PLoS ONE | Year: 2013

The Malagarasi River has long been thought to be a barrier to chimpanzee movements in western Tanzania. This potential geographic boundary could affect chimpanzee ranging behavior, population connectivity and pathogen transmission, and thus has implications for conservation strategies and government policy. Indeed, based on mitochondrial DNA sequence comparisons it was recently argued that chimpanzees from communities to the north and to the south of the Malagarasi are surprisingly distantly related, suggesting that the river prevents gene flow. To investigate this, we conducted a survey along the Malagarasi River. We found a ford comprised of rocks that researchers could cross on foot. On a trail leading to this ford, we collected 13 fresh fecal samples containing chimpanzee DNA, two of which tested positive for SIVcpz. We also found chimpanzee feces within the riverbed. Taken together, this evidence suggests that the Malagarasi River is not an absolute barrier to chimpanzee movements and communities from the areas to the north and south should be considered a single population. These results have important consequences for our understanding of gene flow, disease dynamics and conservation management. © 2013 Piel et al. Source

Debenham J.J.,Norwegian University of Life Sciences | Atencia R.,The Jane Goodall Institute | Midtgaard F.,Norwegian University of Life Sciences | Robertson L.J.,Norwegian University of Life Sciences
Journal of Medical Primatology | Year: 2015

Background: The aim of this study was to investigate the occurrence of Giardia duodenalis and Cryptosporidium spp. in primates and determine their zoonotic or anthropozoonotic potential. Methods: Direct immunofluorescence was used to identify Giardia and Cryptosporidium from faecal samples. PCR and DNA sequencing was performed on positive results. Results: Giardia cysts were identified from 5.5% (5/90) of captive chimpanzees and 0% (0/11) of captive mandrills in the Republic of Congo; 0% (0/10) of captive chimpanzees in Norway; and 0% of faecal samples (n = 49) from wild Zanzibar red colobus monkeys. Two Giardia positive samples were also positive on PCR, and sequencing revealed identical isolates of Assemblage B. Cryptosporidium oocysts were not detected in any of the samples. Conclusions: In these primate groups, in which interactions with humans and human environments are quite substantial, Giardia and Cryptosporidium are rare pathogens. In chimpanzees, Giardia may have a zoonotic or anthropozoonotic potential. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Source

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