Causes, mechanisms and consequences of female competition in red-fronted lemurs

• Applicants: Dr. Claudia Fichtel; Professor Dr. Peter M. Kappeler
• Subject Area: Sensory and Behavioural Biology ; Evolution, Anthropology
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445729110

• Final Report Year: 2024

Final Report Abstract

In the context of mammalian reproduction, female competition is much more pervasive than assumed by classical sex role theory. Episodic targeted aggression among females, which may result in eviction and even death, has been intensively studied in carnivores, but comprehensive field studies of primates are lacking. To begin filling this gap, we conducted a field study of the causes, mechanisms and consequences of female competition in a groupliving primate from Madagascar (redfronted lemurs, Eulemur rufifrons). By combining longterm demographic with behavioral and physiological data we show that female redfronted lemurs target close female kin for forcible, permanent and presumably lethal eviction when groups exceed a critical size of 8-10 individuals, even though groups contain multiple unrelated males. Females were more likely to be evicted from groups with larger numbers of juvenile females, but the identity of evicted females was not predicted by any intrinsic traits. There was no evidence for female reproductive restraint in the form of reduced birth rates that might forestall evictions when the number of adult females was high; in contrast, birth rates were actually higher when there were more adult females in a group and also in years with higher rainfall. Based on 6 years of continuous sample collection, we found that while fecal glucocorticoid metabolite (FGCM) levels increased in both sexes with decreasing fruit consumption, this increase was not accompanied by concomitant changes in agonistic behavior. Female aggression and FGCM levels peaked during the birth season, while for males, aggression remained fairly constant across the year. Our results therefore suggest that redfronted lemurs have mechanisms to avoid direct competition through aggression at times when individuals may need to conserve energy. Analyzing behavioral data collected over 7 years, we found no evidence for significant changes in the coefficient of variation of relationship strength in affiliative interaction networks, as well as in affiliative and agonistic interaction rates, indicating that the disappearance of a group member is not reflected by a change in social interactions. Yet, the fact that rates of social interactions did not change significantly indicates that they compensated for the loss of a group member by redistributing their social behavior towards other individuals. Our study therefore indicates that redfronted lemurs' social interactions are resilient to group member loss. Thus, our study demonstrates a balanced interplay between female reproductive competition, competition over group membership between both sexes, and kin selection, contributing new insights into the causes and consequences of female competition in animal societies.

Publications

• Reproductive Senescence in Two Lemur Lineages. Frontiers in Ecology and Evolution, 10.
  Kappeler, Peter M.; Pethig, Leonie; Prox, Lea & Fichtel, Claudia
  
• Drivers and consequences of female reproductive competition in an egalitarian, sexually monomorphic primate. Behavioral Ecology and Sociobiology, 77(5).
  Prox, Lea; Fichtel, Claudia & Kappeler, Peter M.
  
• Who cares? Behavioural consequences of social disruptions in redfronted lemurs, Eulemur rufifrons. Animal Behaviour, 196, 9-21.
  Pfaff, Amrei; Prox, Lea; Fichtel, Claudia & Kappeler, Peter M.
  
• Causes and consequences of female competition in redfronted lemurs (Eulemur rufifrons). University Goettingen Repository.
  Prox, Lea-Maria