Machos or Don Juans? The reproductive tactics of male bonobos (Pan paniscus) in captivity.

摘要

Bonobos have long time been considered as a promiscuous species with little male-male competition over access to females. Recent evidence suggests however that competition is more important than previously stated. Moreover, female mate choice may also influence male mating success since females can occupy high ranking positions in the hierarchy. Males may therefore have to invest in affiliation with females because sexual coercion (forced copulations, infanticide) may be more difficult.; I investigated to what extent male mating success in influenced by contest competition (Macho tactic) and/or intersexual affiliation (Don Juan tactic). I studied several multi-male groups of bonobos in captivity (Wuppertal, Germany; Apenheul, The Netherlands; Twycross Zoo, United Kingdom; Planckendael Wild Animal Park, Belgium). This relatively large sample size also allowed me to test hypotheses about dominance relations and social structures in captive bonobo groups.; In the first part it is shown that in all groups a linear hierarchy was found in which females occupy the highest ranking positions, but some males nonetheless dominate some females. Moreover, a new methodology to measure "steepness" of hierarchies showed that males on average have steeper, more despotic dominance relationships than females.; In the second part I investigated social structures and found that female bonding in captive groups of bonobos is not necessarily stronger than bonding between unrelated males and females. Moreover, the exchange of affiliative behaviours, such as grooming and support are influenced by the steepness of dominance hierarchies in the respective study groups.; The results of the third section show that competition among males is more prominent in captive bonobos than previously stated. Aggression increased in the presence of females with a maximal swelling in two study groups. Males harassed copulations relatively frequently. Only in one group did a dominant male obtain the highest number of copulation bouts. Female mate choice predicted male mating success in two groups. When females showed a preference for the alpha male, lower ranking males were found to increase their grooming efforts, which is in accordance with predictions of biological market theories.