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Abstract Female reproductive maturation is a critical life-history milestone, initiating an individual’s reproductive career. Studies in social mammals have often focused on how variables related to nutrition influence maturation age in females. However, parallel investigations have identified conspicuous male-mediated effects in which female maturation is sensitive to the presence and relatedness of males. Here, we evaluated whether the more “classic” socioecological variables (i.e., maternal rank, group size) predict maturation age in wild geladas—a primate species with known male-mediated effects on maturation and a grassy diet that is not expected to generate intense female competition. Females delayed maturation in the presence of their fathers and quickly matured when unrelated, dominant males arrived. Controlling for these male effects, however, higher-ranking daughters matured at earlier ages than lower-ranking daughters, suggesting an effect of within-group contest competition. However, contrary to predictions related to within-group scramble competition, females matured earliest in larger groups. We attribute this result to either: 1) a shift to “faster” development in response to the high infant mortality risk posed by larger groups; or 2) accelerated maturation triggered by brief, unobserved male visits. While earlier ages at maturation were indeed associated with earlier ages at first birth, these benefits were occasionally offset by male takeovers, which can delay successful reproduction via spontaneous abortion. In sum, rank-related effects on reproduction can still occur even when socioecological theory would predict otherwise, and males (and the risks they pose) may prompt female maturation even outside of successful takeovers.
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Living with males leads to female physical injury in the leaf-footed cactus bug
Abstract Males in many species possess sexually selected weapons that they use to fight for mating opportunities. It is well established that male-male competition can lead to physical injuries for males. However, very few studies have looked at the physical consequences for conspecific females. We hypothesized that living with males in a species with male-male competition would result in female injury. Because larger female invertebrates typically have greater reproductive output, they have higher resource value for males and can elicit aggression and fighting. Thus, we further hypothesized that larger females in this context would receive more injuries. For this study, we focused on the leaf-footed cactus bug, Narnia femorata (Hemiptera: Coreidae), a species of insect in which males fight using their spiny and enlarged hindlegs. In just 2 h of observation, we documented males competing with other males in 61% of 103 trials. In 43% of these 63 competitions, females were physically contacted and sometimes attacked with a kick or squeeze. We left insects in social groups for 74 h and found that females living with multiple males had a higher likelihood of obtaining injuries (26.2% of 103 trials) compared to those living only with females (9.7% of 103 trials). In addition, larger females were more likely to be injured compared to smaller females. Our study highlights the harm that females can experience in species with male-male competition.
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- Award ID(s):
- 2226881
- PAR ID:
- 10610951
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Behavioral Ecology
- Volume:
- 36
- Issue:
- 4
- ISSN:
- 1045-2249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Introduction Dominance relationships in which females dominate males are rare among mammals. Mechanistic hypotheses explaining the occurrence of female dominance suggest that females dominate males because (1) they are intrinsically more aggressive or less submissive than males, and/or (2) they have access to more social support than males. Methods Here, we examine the determinants of female dominance across ontogenetic development in spotted hyenas ( Crocuta crocuta ) using 30 years of detailed behavioral observations from the Mara Hyena Project to evaluate these two hypotheses. Results Among adult hyenas, we find that females spontaneously aggress at higher rates than males, whereas males spontaneously submit at higher rates than females. Once an aggressive interaction has been initiated, adult females are more likely than immigrant males to elicit submission from members of the opposite sex, and both adult natal and immigrant males are more likely than adult females to offer submission in response to an aggressive act. We also find that adult male aggressors are more likely to receive social support than are adult female aggressors, and that both adult natal and immigrant males are 2–3 times more likely to receive support when attacking a female than when attacking another male. Across all age classes, females are more likely than males to be targets of aggressive acts that occur with support. Further, receiving social support does slightly help immigrant males elicit submission from adult females compared to immigrant males acting alone, and it also helps females elicit submission from other females. However, adult females can dominate immigrant males with or without support far more often than immigrant males can dominate females, even when the immigrants are supported against females. Discussion Overall, we find evidence for both mechanisms hypothesized to mediate female dominance in this species: (1) male and female hyenas clearly differ in their aggressive and submissive tendencies, and (2) realized social support plays an important role in shaping dominance relationships within a clan. Nevertheless, our results suggest that social support alone cannot explain sex-biased dominance in spotted hyenas. Although realized social support can certainly influence fight outcomes among females, adult females can easily dominate immigrant males without any support at all.more » « less
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