Male dominance rank and reproductive success in chimpanzees, Pan troglodytes schweinfurthii

Abstract

Competition for fertile females determines male reproductive success in many species. The priority of access model predicts that male dominance rank determines access to females, but this model has been difficult to test in wild populations, particularly in promiscuous mating systems. Tests of the model have produced variable results, probably because of the differing socioecological circumstances of individual species and populations. We tested the predictions of the priority of access model in the chimpanzees of Gombe National Park, Tanzania. Chimpanzees are an interesting species in which to test the model because of their fission-fusion grouping patterns, promiscuous mating system and alternative male mating strategies. We determined paternity for 34 offspring over a 22-year period and found that the priority of access model was generally predictive of male reproductive success. However, we found that younger males had higher success per male than older males, and low-ranking males sired more offspring than predicted. Low-ranking males sired offspring with younger, less desirable females and by engaging in consortships more often than high-ranking fathers. Although alpha males never sired offspring with related females, inbreeding avoidance of high-ranking male relatives did not completely explain the success of low-ranking males. While our work confirms that male rank typically predicts male chimpanzee reproductive success, other factors are also important; mate choice and alternative male strategies can give low-ranking males access to females more often than would be predicted by the model. Furthermore, the success of younger males suggests that they are more successful in sperm competition. Keywords chimpanzee; dominance rank; male reproductive success; Pan troglodytes schweinfurthii; paternity; priority of access Among mammals, males usually compete over access to fertile females (Trivers 1972;Cunningham & Birkhead 1998). Accordingly, there is a well-documented relationship between male dominance rank and reproductive success in many group-living species (e.g. red deer, Cervus elaphus: Pemberton et al. 1992; northern elephant seals, Mirounga angustirostris: Haley et al. 1994; African wild dogs, Lycaon pictus: Girman et al. 1997). In these species and * Correspondence: E. E. Wroblewski, Department of Ecology, Evolution, and Behavior, University of Minnesota, 100 Ecology Building, 1987 Upper Buford Circle, St Paul, MN 55108, U.S.A. E-mail address: E-mail: wrob0042@umn.edu (E.E. Wroblewski). (Berard et al. 1994;Soltis et al. 2001). The degree to which these factors are important is probably contingent upon the socioecology of the species or population. NIH Public AccessChimpanzees represent a particularly interesting system in which to investigate the applicability of the priority of access model. Unlike the primate species referenced above, chimpanzees live in a fission-fusion social system in which subgroups, known as parties, are temporary within a permanent community (Nishida 1968;Goodall 19...

Group augmentation, collective action, and territorial boundary patrols by male chimpanzees

“…High-ranking males often sire many offspring, but a positive relationship between rank and participation in patrols that occurs independently of rank-related variation in reproductive success would indicate that relative paternity success is an insufficient explanation for variation in patrolling (48,(55)(56)(57)(58). One likely possibility is that high-ranking individuals experience relatively low costs of patrolling because of their superior physical condition (59)(60)(61).…”

Female parity, male aggression, and the Challenge Hypothesis in wild chimpanzees

“…Moreover, females give birth only once every 5-6 years (Goodall 1986;Boesch and Boesch-Achermann 2000;Nishida et al 2003;Sugiyama 2004), leading to an operational sex ratio that is skewed heavily toward males (Emlen and Oring 1977). As a consequence, males compete vigorously to obtain mating and reproductive opportunities with estrous females who are available only rarely (Boesch et al 2006;Inoue et al 2008;Wroblewski et al 2009;Newton-Fisher et al 2010). Aggression associated with reproductive competition can be extremely intense, especially for older, parous females, who have already reproduced successfully (Muller et al 2006).…”

Cooperation and competition in chimpanzees: Current understanding and future challenges

“…46,[51][52][53] Recent research from several sites now indicates that males achieving high dominance rank obtain substantial fitness benefits, with alpha males siring up to 30%-50% of all infants born during their tenures at the top of hierarchies. [53][54][55][56] Male chimpanzees also compete with conspecifics from other communities as they defend their feeding grounds via group territorial behavior. 57 Despite their highly competitive nature, male chimpanzees also cooperate in several contexts to obtain direct and indirect fitness benefits.…”