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1. Orphaning stunts growth in wild African elephants

   https://doi.org/10.1093/conphys/coac053  

   Parker, Jenna M ; Wittemyer, George ( January 2022 , Conservation Physiology)

   Fuller, Andrea (Ed.)

   Orphans of several species suffer social and physiological consequences such as receiving more aggression from conspecifics and lower survival. One physiological consequence of orphaning, stunted growth, has been identified in both humans and chimpanzees, but has not been assessed in a non-primate species. Here, we tested whether wild African elephant orphans show evidence of stunted growth. We measured individually known female elephants in the Samburu and Buffalo Springs National Reserves of Kenya, with a rangefinder capable of calculating height, to estimate a von Bertalanffy growth curve for female elephants of the study population. We then compared measurements of known orphans and non-orphans of various ages, using a Bayesian analysis to assess variation around the derived growth curve. We found that orphans are shorter for their age than non-orphans. However, results suggest orphans may partially compensate for stunting through later growth, as orphans who had spent a longer time without their mother had heights more similar to non-orphans. More age mates in an individual’s family were associated with taller height, suggesting social support from peers may contribute to increased growth. Conversely, more adult females in an individual’s family were associated with shorter height, suggesting within-group competition for resources with older individuals may reduce juvenile growth. Finally, we found a counterintuitive result that less rainfall in the first 6 years of life was correlated with taller height, potentially reflecting the unavoidable bias of measuring individuals who were fit enough to survive conditions of low rainfall as young calves. Reduced growth of individuals has been shown to reduce survival and reproduction in other species. As such, stunting in wildlife orphans may negatively affect fitness and represents an indirect effect of ivory poaching on African elephants. 

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2. Social dominance and cooperation in female vampire bats

   https://doi.org/10.1098/rsos.210266  

   Crisp, Rachel J. ; Brent, Lauren J. ; Carter, Gerald G. ( July 2021 , Royal Society Open Science)

   When group-living animals develop individualized social relationships, they often regulate cooperation and conflict through a dominance hierarchy. Female common vampire bats have been an experimental system for studying cooperative relationships, yet surprisingly little is known about female conflict. Here, we recorded the outcomes of 1023 competitive interactions over food provided ad libitum in a captive colony of 33 vampire bats (24 adult females and their young). We found a weakly linear dominance hierarchy using three common metrics (Landau's h ’ measure of linearity, triangle transitivity and directional consistency). However, patterns of female dominance were less structured than in many other group-living mammals. Female social rank was not clearly predicted by body size, age, nor reproductive status, and competitive interactions were not correlated with kinship, grooming nor food sharing. We therefore found no evidence that females groomed or shared food up a hierarchy or that differences in rank explained asymmetries in grooming or food sharing. A possible explanation for such apparently egalitarian relationships among female vampire bats is the scale of competition. Female vampire bats that are frequent roostmates might not often directly compete for food in the wild. 

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3. Evaluating drivers of female dominance in the spotted hyena

   https://doi.org/10.3389/fevo.2022.934659  

   McCormick, S. Kevin ; Laubach, Zachary M. ; Strauss, Eli D. ; Montgomery, Tracy M. ; Holekamp, Kay E. ( December 2022 , Frontiers in Ecology and Evolution)

   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. 

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4. Sociosexual behavioral patterns involving nulliparous female orangutans ( Pongo sp.) reflect unique challenges during the adolescent period

   https://doi.org/10.1002/ajp.23058  

   O'Connell, Caitlin A. ; Susanto, Tri Wahyu ; Knott, Cheryl D. ( October 2019 , American Journal of Primatology)

   The primate adolescent period is characterized by a series of changes in physiology, behavior, and social relationships. Orangutans have the slowest life history and the longest period of dependency of all primates. As members of a semisolitary species with high levels of sexual coercion, adolescent female orangutans face a unique combination of challenges when achieving independence from their mother. This study examined the mating behavior of adolescent female orangutans and compared it with that of adult females to assess whether mating behavior reflects distinct strategies at these different points in the life cycle. Data were collected in Gunung Palung National Park on the island of Borneo over 20 years. Mating events from adolescent (n = 19) and adult females (n = 26) were scored and compared. Adolescent female mating events had significantly higher mating scores (indicating more proceptivity) than those of adult females (β = 1.948,p = .001). Adolescent females also engaged in elaborate sociosexual interactions with different flanged males, behaviors that were never observed during mating events of adult females. These interactions involved characteristic behavior on the part of both the adolescent females and the flanged males. Given these findings and the documentation of similar accounts of adolescent female–flanged male mating from the island of Sumatra, we propose that adolescent female orangutans display distinctive behavioral repertoires throughout the genusPongowhich serves to overcome male ambivalence toward nulliparous females, establish familiarity, and evaluate coercive tendencies in flanged males. We suggest that these behavioral patterns are an integral part of female social development in a female philopatric, but highly dispersed species where consistent social support is absent after ranging independence is achieved.

    

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5. Orange ornamentation increases sex-specific conspicuousness of juvenile males to conspecifics and predators

   https://doi.org/10.1093/biolinnean/blae035  

   Agan, Jaina ; Macedonia, Joseph M. ; Grindstaff, Jennifer L. ; Fox, Stanley F. ( April 2024 , Biological Journal of the Linnean Society)

   Many animal species have evolved striking colour patterns that attract the opposite sex and intimidate rivals. Although conspicuous coloration is usually restricted to adults in the context of reproduction, this is not always the case. Juvenile collared lizards (Crotaphytus collaris) are sexually dichromatic, wherein males exhibit ‘dorsolateral bars’ that are bright orange and showy, whereas females are light tan and inconspicuous. Given that adult male collared lizards suffer increased predation because of bright adult coloration, we hypothesized that juvenile males might also be more detectable to predators owing to the conspicuousness of their dorsolateral bars. To test this hypothesis, we measured the reflectance of the dorsolateral bars, non-bar background body regions, and the rocky habitat in which the lizards live. We modelled the vision of our study species and its dominant predators to quantify and compare statistically the contrasts of male and female dorsolateral bars against the natural rock background. We also calculated lizard survivorship over a 4 year study period. We found that male orange bars exhibited significantly higher chromatic contrast, but significantly lower achromatic contrast, than female bars when perceived through all visual models. However, the dorsolateral background colour of juvenile males and females did not differ significantly in chromatic or achromatic contrast from rocks in any visual model. Female lizards survived better than male lizards to the yearling (reproductive) stage. Our findings indicate that juvenile male bars are conspicuous both to conspecifics and to predators and that the bars probably increase predation on juvenile males.

    

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