Person: Thompson, Melissa Emery
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Melissa Emery
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Thompson, Melissa Emery
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Publication Sexual Coercion by Male Chimpanzees Shows That Female Choice May Be More Apparent than Real(Springer, 2011) Muller, Martin N.; Thompson, Melissa Emery; Kahlenberg, Sonya Marie; Wrangham, RichardThe extent to which active female mating preferences influence male reproductive success in mammals is unclear, particularly for promiscuously breeding species like chimpanzees (Pan troglodytes). Previous studies from multiple long-term study sites have shown that female chimpanzees mate more restrictively around ovulation, and this has been taken as evidence for female choice. However, none of these studies rigorously evaluated the alternative hypothesis that restrictive mating results not from unconstrained choice, but in response to coercive mate guarding, in which males use punishment and intimidation to reduce female promiscuity and promote their own mating interests. Nor did they consider evidence for the potential genetic or phenotypic benefits that females might be choosing. Using 11 years of data from the Kanyawara community in Kibale National Park, Uganda, we previously demonstrated that males achieve elevated mating success with those females toward whom they direct high levels of aggression. Here we extend those findings to show that even female copulatory approaches, which have previously been attributed to female choice, are correlated with male aggression. Specifically, individual females at our site initiated periovulatory copulations most frequently with the males who were most aggressive toward them throughout their cycles. Those males showed high rates of aggression toward females throughout estrus, despite achieving high copulation rates, demonstrating a continuing conflict of interest over the exclusivity of mating access. Because sexual coercion is potentially widespread in primates and other mammals, our results stress the importance of considering the influence of male aggression in studies of female choice.Publication Diet and Reproductive Function in Wild Female Chimpanzees (Pan Troglodytes Schweinfurthii)at Kibale National Park, Uganda(Wiley-Blackwell, 2008) Thompson, Melissa Emery; Wrangham, RichardHuman female reproductive function is highly sensitive to current energetic condition, indicating adaptation to modulate reproductive effort in accordance with changing ecological conditions that might favor or disfavor the production of offspring. Here, we test the hypothesis that reproductive capacity in female chimpanzees is likewise limited by current energetic condition. We used 12 years of data on wild chimpanzees (Pan troglodytes schweinfurthii) in the Kanyawara community of Kibale National Park, Uganda, to examine the relationship of dietary quality, as assessed by fruit components of the diet, to the occurrence of sexually receptive females, concentrations of ovarian steroid hormones, and timing of conception. We found that the frequency of females having sexual swellings was positively related to the consumption of drupe fruits. Estrogen levels of both cycling and noncycling females increased during seasonal peaks in the consumption of drupe fruits. When average fruit consumption remained high across months, females conceived more quickly. These results support the hypothesis that cycling and conception in chimpanzees are contingent upon high energy balance, and they indicate that the availability of fruit is a key variable limiting reproductive performance in chimpanzees. Chimpanzees appear to share with humans a reproductive system that is primed to respond to proximate levels of energy acquisition.Publication Urinary C-Peptide Tracks Seasonal and Individual Variation in Energy Balance in Wild Chimpanzees(Elsevier, 2009) Thompson, Melissa Emery; Muller, Martin N.; Wrangham, Richard; Lwanga, Jeremiah S.; Potts, Kevin B.C-peptide of insulin presents a promising new tool for behavioral ecologists that allows for regular, noninvasive assessment of energetic condition in wild animals. C-peptide is produced on an equimolar basis with insulin, thus is indicative of the body's response to available glucose and, with repeated measurement, provides a biomarker of energy balance. As yet, few studies have validated the efficacy of C-peptide for monitoring energy balance in wild animals. Here, we assess seasonal and interindividual variation in urinary C-peptide concentrations of East African chimpanzees (Pan troglodytes schweinfurthii). We assayed 519 urine samples from 13 adult male chimpanzees in the Kanyawara community of Kibale National Park, Uganda. Cpeptide levels were significantly predicted by the total amount of fruit and the amount of preferred fruit in the diet. However, chimpanzees had very low c-peptide titers during an epidemic of severe respiratory illness, despite highly favorable feeding conditions. Kanyawara males had significantly lower C-peptide levels than males at Ngogo, a nearby chimpanzee community occupying a more productive habitat. Among Kanyawara males, low-ranking males had consistently higher C-peptide levels than dominant males. While counterintuitive, this result supports previous findings of costs associated with dominance in male chimpanzees. Our preliminary investigations demonstrate that C-peptide has wide applications in field research, providing an accessible tool for evaluating seasonal and individual variation in energetic condition, as well as the costs of processes such as immune function and reproduction.Publication Immigration Costs for Female Chimpanzees and Male Protection as an Immigrant Counterstrategy to Intrasexual Aggression(Elsevier, 2008) Kahlenberg, Sonya Marie; Thompson, Melissa Emery; Muller, Martin N.; Wrangham, RichardIn chimpanzees, Pan troglodytes, females transfer from their natal group shortly after sexual maturity to permanently join another group. A conflict of interest exists between female and male residents over the immigration of new females: additional females increase female feeding competition but provide new mating opportunities for males. Resident females express their interests by directing high rates of aggression towards immigrants, and males could protect their interests by intervening in these conflicts. We studied the Kanyawara chimpanzee community in Kibale National Park, Uganda over 10.5 years to assess whether (1) resident female aggression is costly to immigrants, (2) males are effective in protecting immigrants from aggression and (3) immigrants seek out male protective services. Results showed costs of resident aggression on two levels. Immigrants held low dominance ranks and experienced higher physiological stress than natal residents, as indexed by urinary cortisol. Males were found to be effective protectors for immigrants. They intervened aggressively to curtail female conflicts, more often when conflicts involved immigrants and occurred during periods of heightened female competition. When intervening, males nearly always supported immigrants over residents. As a result, females, especially immigrants, experienced less intrasexual aggression in the presence of males than when males were absent. Immigrants took advantage of male protective services. They associated with males more often than resident females and, unlike residents, did not greatly decrease their level of association outside of oestrus. We suggest male protection is an important strategy used by immigrants to integrate themselves into their new group.Publication Male Mating Interest Varies with Female Fecundity in Pan Troglodytes Schweinfurthii of Kanyawara, Kibale National Park(Springer Verlag, 2008) Thompson, Melissa Emery; Wrangham, RichardFemale chimpanzees mate promiscuously during a period of extended receptivity marked by prominent sexual swelling. Recent studies of wild chimpanzees indicate that subtle variations in swelling size could act as a reliable cue of female fertilization potential both within and between cycles (Emery and Whitten Behavioral Ecology and Sociobiology, 54, 340–351, 2003; Deschner et al. Hormones and Behavior, 46, 204–215, 2004). Copulation rates increase during the periovulatory period and during conception cycles (Deschner et al. Hormones and Behavior, 46, 204–215, 2004; Emery Thompson American Journal of Primatology, 67, 137–158, 2005a), suggesting that males may be able to assess female fertilization potential. We asked whether facultative timing of copulation in Kanyawara chimpanzees was due to increased male mating interest or to increased female proceptivity during the most fecund days. We assessed multiple measures of male mating effort in cycles aligned relative to the day of detumescence and compared periovulatory days to other days of maximal swelling, and conception cycles to nonconception cycles. The rate and proportion of male initiative in soliciting sexual behavior increased during periods of highest fertilization potential. Males were also more likely to interrupt copulations, associate with estrous females, and compete with other males when females were most likely to conceive. Females initiated copulations more frequently during conception cycles but did not visibly shift mating behavior within cycles. Our results support the hypothesis that male chimpanzees have the ability to assess the profitability of mating attempts, a trait that may act as a counter-adaptation to female strategies to obscure paternity. We discuss potential cues and the implications for female reproductive strategies.Publication Female Competition over Core Areas in Pan Troglodytes Schweinfurthii, Kibale National Park, Uganda(Springer Verlag, 2008) Kahlenberg, Sonya Marie; Thompson, Melissa Emery; Wrangham, RichardAggression is rare among wild female chimpanzees. However, in the Kanyawara chimpanzee community in Kibale National Park, Uganda, stable use of food-rich core areas is linked to increased reproductive success, suggesting that contest competition might occur over access to the highest-quality ranges. To examine this hypothesis, we studied aggression and dominance relationships among Kanyawara females during a 10-yr period that included the immigration of 5 females into the community. We tested 2 predictions: 1) that female-female aggression should intensify when immigrants enter the community because this is when core area access is determined and 2) that the quality of core areas should reflect relative female dominance relationships. In support of the first prediction, female-female aggression increased 4-fold when new immigrants were in the community, with rates peaking when there were multiple immigrants. This pattern was due primarily to aggression by resident mothers toward immigrants and featured coalitionary aggression, a rare behavior among female chimpanzees. In support of the second prediction, females occupying core areas high in foraging quality ranked high overall and higher than expected for their ages, whereas females occupying low-quality core areas were lower-ranking and ranked lower than expected for their ages. Together, the data indicate that though female aggression does not regularly occur in chimpanzees, contest competition continues to play an important role in determining long-term access to resources, an important correlate of reproductive success.