Mountain gorilla tug-of-war: Silverbacks have limited control over reproduction in multimale groups

doi:10.1073/pnas.0502019102

Mountain gorilla tug-of-war: Silverbacks have limited control over reproduction in multimale groups

^*Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103 Leipzig, Germany; ^‡Dian Fossey Gorilla Fund International, Atlanta, GA 30315-1440; ^§Department of Psychology, University of Stirling, Stirling FK9 4LA, United Kingdom; and ^¶Department of Anthropology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903-0270

Edited by Frans B. M. de Waal, Emory University, Atlanta, GA (received for review March 11, 2005)

Abstract

To determine who fathers the offspring in wild mountain gorilla groups containing more than one adult male silverback, we genotyped nearly one-fourth (n = 92) of the mountain gorillas (Gorilla beringei beringei) living in the Virunga Volcanoes region of Africa. Paternity analysis of 48 offspring born into four groups between 1985 and 1999 revealed that, although all infants were sired by within-group males, the socially dominant silverback did not always monopolize reproduction within his group. Instead, the second-ranking male sired an average of 15% of group offspring. This result, in combination with previous findings that second-ranking males fare best by not leaving the group but by staying and waiting to assume dominance even if no reproduction is possible while waiting, is not consistent with expectations from a reproductive skew model in which the silverback concedes controllable reproduction to the second-ranking male. Instead, the data suggest a “tug-of-war” scenario in which neither the dominant nor the second-ranking male has full control over his relative reproductive share. The two top-ranked males were typically unrelated and this, in combination with the mixed paternity of group offspring, means that multimale gorilla groups do not approximate family groups. Instead, as long-term assemblages of related and unrelated individuals, gorilla groups are similar to chimpanzee groups and so offer interesting possibilities for kin-biased interactions among individuals.

Footnotes

↵ ∥ To whom correspondence should be addressed. E-mail: vigilant{at}eva.mpg.de.
↵ † Present address: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviation: R, relatedness.