Agonism can also have profound reproductive consequences when fetuses and infants are targeted during aggressive interactions. In group-living mammals, inducing miscarriage in pregnant individuals may benefit males and females alike if the death of the infant returns the mother to estrous and removes a future competitor. Abortion in response to the arrival of a new male—termed the “Bruce effect”—has been widely documented, but evidence from wild populations is rare, and, though aggression between unrelated females in social groups is common, the consequences of these encounters for pregnant females and the strategies they may employ to ameliorate these costs remain poorly understood. In several non-human primates, aggression between adult males often involves the utilization of infants as agonistic “buffers”, further endangering the reproductive output of mothers. This dissertation explores the relationship between conspecific aggression and the survival of infants and fetuses in captive and wild olive baboons, Papio anubis, and investigates the role maternal kin and fathers may have in protecting these vulnerable group members. Long-term data collected on wild baboons in Gombe National Park, Tanzania provide a lens through which to explore overall trends in reproductive output and family relationships, while focal follows give fine-scale understanding of rates of behavior. I also conducted color manipulation and playback experiments on captive baboons to assess how females may use color and vocal signals to recruit help from potential fathers and maternal kin. Chapter 1 reveals that bright colors signaling pregnancy may deter attackers, but that kin may play an important role in the efficacy of this signal. Chapter 2 assesses the role of maternal kin and potentially infanticidal males, and finds little evidence kin support is vital for avoiding miscarriage. However, the risk of fetal loss rises for pregnant females exposed to new immigrants that ascend rank quickly. Chapter 3 investigates the impact of male use of infants during agonistic encounters and suggests that, though this infant carrying behavior may have roots in paternal protection, new immigrant males can exploit this signal to the mortal detriment of the infants involved. Together, these chapters identify several reproductive costs for mothers at the hands of aggressive group members and highlight the possible pervasiveness of evolutionarily selected signals of pregnancy, male-induced abortion, and the use of “living tools” to signal aggressive intent.
University of Minnesota Ph.D. dissertation. December 2015. Major: Ecology, Evolution and Behavior. Advisors: Craig Packer, Michael Wilson. 1 computer file (PDF); vi, 69 pages.
Conspecific aggression as a reproductive constraint and the value of kin in olive baboons, Papio anubis.
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