The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


Female rank and infanticide in Nepal Gray langurs

CAROLA BORRIES1,2 and ANDREAS KOENIG1,2.

1Department of Anthropology, Stony Brook University, 2Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University

March 26, 2015 , Archview Ballroom Add to calendar

In several matrilineal cercopithecine primates female dominance rank translates into improved access to food, better nutritional condition, and even higher reproductive success. The benefits of an age-inversed hierarchy as described for female langurs are, however, less well understood. The youngest reproducing females occupy the highest ranks and older females are found at the bottom of the hierarchy. This system is inherently unstable and rank changes much more frequently compared to matrilineal cercopithecines. Nevertheless, in a given situation, most dominance relationships are decided and hierarchies are linear bearing the question what the potential benefits of rank may be in such a system? Here we investigated if maternal rank affects the rate of infanticide using data for two wild multimale groups of Nepal Gray langurs (Semnopithecus schistaceus) from Ramnagar, Nepal. In this population infanticide by adult males accounted for 32% of infant mortality. Between 1991 and 1996, 35 attacks/infanticides were documented. In 29 of these cases data on dyadic displacement interactions were available so that maternal rank could be determined. Females were divided into 2 rank classes (low and high). Compared to all infants present, offspring of low-ranking mothers were targeted significantly more frequently by males (G-test, p’s < 0.01). Of the 6 infants who died, 5 had a low-ranking mother. Together, this suggests a strong effect of maternal rank on offspring survival although the proximate mechanisms still have to be disclosed. Future studies will have to show if infanticide avoidance can be added as potential rank benefit in nonhuman primates.

Supported by the German Research Council (DFG, Vo124/19-1+2, Wi966/4-3) and the Alexander von Humboldt-Foundation (AvH).