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1. Sex bias in mortality risk changes over the lifespan of bottlenose dolphins

   https://doi.org/10.1098/rspb.2023.0675  

   McEntee, Molly H.; Foroughirad, Vivienne; Krzyszczyk, Ewa; Mann, Janet (July 2023, Proceedings of the Royal Society B: Biological Sciences)

   Research on sex biases in longevity in mammals often assumes that male investment in competition results in a female survival advantage that is constant throughout life. We use 35 years of longitudinal data on 1003 wild bottlenose dolphins ( Tursiops aduncus ) to examine age-specific mortality, demonstrating a time-varying effect of sex on mortality hazard over the five-decade lifespan of a social mammal. Males are at higher risk of mortality than females during the juvenile period, but the gap between male and female mortality hazard closes in the mid-teens, coincident with the onset of female reproduction. Female mortality hazard is non-significantly higher than male mortality hazard in adulthood, resulting in a moderate male bias in the oldest age class. Bottlenose dolphins have an intensely male-competitive mating system, and juvenile male mortality has been linked to social competition. Contrary to predictions from sexual selection theory, however, male–male competition does not result in sustained male-biased mortality. As female dolphins experience high costs of sexual coercion in addition to long and energetically expensive periods of gestation and lactation, this suggests that substantial female investment in reproduction can elevate female mortality risk and impact sex biases in lifespan. 

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2. Sex-specific consequences of juvenile dispersal for survival and reproduction in an island lizard

   https://doi.org/10.1093/beheco/araf103  

   Crain, C Ashlyn; Wittman, Tyler N; Bhave, Rachana S; Seears, Heidi A; Reedy, Aaron M; Warner, Daniel A; Cox, Robert M (September 2025, Behavioral Ecology)

   While, Geoffrey (Ed.)

   Abstract Dispersal is a costly, though potentially rewarding, behavior with important fitness consequences for juveniles. When the costs or benefits of juvenile dispersal differ between sexes, sex-biased dispersal should be favored, though such sex-specific consequences are rarely measured for multiple components of lifetime fitness in the wild. Here, we use detailed mark–recapture data from 4 annual cohorts of juveniles with associated estimates of juvenile survival and adult reproductive success from genetic parentage to measure natural selection on 2 dispersal phenotypes (binary dispersal propensity and continuous dispersal distance) in an island population of lizards (Anolis sagrei). Juvenile dispersal was consistently male-biased, with males exhibiting a higher propensity to disperse and dispersing twice as far as females. Males that dispersed had higher survival to adulthood and total fitness than males that remained philopatric, whereas fitness components did not differ between dispersing and philopatric females. Although this result indicates that the fitness benefits of dispersal are sex-specific, we found no difference in fitness components between dispersing and philopatric males after accounting for body size, which was positively correlated with dispersal. Likewise, we did not consistently detect direct selection on dispersal distance in either sex when including body size in multivariate selection analyses, nor did we find consistent correlational selection on combinations of body size and dispersal distance in either sex. We conclude that selection on juvenile dispersal propensity is sex-specific, but likely indirect and mediated through its positive association with body size in males. 

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3. Sex, synchrony, and skin contact: integrating multiple behaviors to assess pathogen transmission risk

   https://doi.org/10.1093/beheco/araa002  

   Leu, Stephan T; Sah, Pratha; Krzyszczyk, Ewa; Jacoby, Ann-Marie; Mann, Janet; Bansal, Shweta (February 2020, Behavioral Ecology)

   Barrett, Louise (Ed.)

   Abstract Direct pathogen and parasite transmission is fundamentally driven by a population’s contact network structure and its demographic composition and is further modulated by pathogen life-history traits. Importantly, populations are most often concurrently exposed to a suite of pathogens, which is rarely investigated, because contact networks are typically inferred from spatial proximity only. Here, we use 5 years of detailed observations of Indo-Pacific bottlenose dolphins (Tursiops aduncus) that distinguish between four different types of social contact. We investigate how demography (sex and age) affects these different social behaviors. Three of the four social behaviors can be used as a proxy for understanding key routes of direct pathogen transmission (sexual contact, skin contact, and aerosol contact of respiratory vapor above the water surface). We quantify the demography-dependent network connectedness, representing the risk of exposure associated with the three pathogen transmission routes, and quantify coexposure risks and relate them to individual sociability. Our results suggest demography-driven disease risk in bottlenose dolphins, with males at greater risk than females, and transmission route-dependent implications for different age classes. We hypothesize that male alliance formation and the divergent reproductive strategies in males and females drive the demography-dependent connectedness and, hence, exposure risk to pathogens. Our study provides evidence for the risk of coexposure to pathogens transmitted along different transmission routes and that they relate to individual sociability. Hence, our results highlight the importance of a multibehavioral approach for a more complete understanding of the overall pathogen transmission risk in animal populations, as well as the cumulative costs of sociality. 

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4. Caught in the middle: Variation in the physical and behavioral development of male olive baboons (Papio anubis)

   Hawks, Kale A; Most, Corinna A (March 2024, American journal of biological anthropology)

   Male baboons mature more slowly than females, reaching full adult maturity at around 10-12 years of age. After the onset of puberty at 5-7 years, the sub-adult period lasts 3-5 years while the male continues to grow, though there is considerable variation between individuals. Here, we present data on the behavioral changes that accompany the physical maturation of male olive baboons (Papio anubis) as they transition through each developmental stage. This research was conducted on a fully habituated wild troop at the Uaso Ngiro Baboon Project in Laikipia, Kenya. We use long-term grooming data (2018-2023) to show that males have significantly more grooming partners as they get older (n=48, p<.001). We then use behavioral data collected in June and July 2023 to compare the social behaviors of males from three developmental stages: juveniles (n=5), males who recently became sub-adults (n=4), and males who have been sub-adults for over a year (n=5). The differences between these three groups show the effect of puberty on behavior: juveniles were observed in social play significantly more often than sub-adults (p=.006), while males who recently underwent puberty tended to groom less often than either juveniles or older sub-adults (p=.091). Our focal data also revealed variation in the age at which males reached each developmental stage. Further research is needed to determine causes and consequences of the variation in age at puberty and the potential long-term consequences of this variation on the males’ social behavior. 

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5. The cost of associating with males for Bornean and Sumatran female orangutans: a hidden form of sexual conflict?

   https://doi.org/10.1007/s00265-020-02948-4  

   Kunz, Julia A.; Duvot, Guilhem J.; van Noordwijk, Maria A.; Willems, Erik P.; Townsend, Manuela; Mardianah, Neneng; Utami Atmoko, Sri Suci; Vogel, Erin R.; Nugraha, Taufiq Purna; Heistermann, Michael; et al (January 2021, Behavioral Ecology and Sociobiology)

   null (Ed.)

   Abstract Sexual coercion, in the form of forced copulations, is relatively frequently observed in orangutans and generally attributed to their semi-solitary lifestyle. High ecological costs of association for females may be responsible for this lifestyle and may have prevented the evolution of morphological fertility indicators (e.g., sexual swellings), which would attract (male) associates. Therefore, sexual conflict may arise not only about mating per se but also about associations, because males may benefit from associations with females to monitor their reproductive state and attempt to monopolize their sexual activities. Here, we evaluate association patterns and costs for females when associating with both males and females of two different orangutan species at two study sites: Suaq, Sumatra ( Pongo abelii ), and Tuanan, Borneo ( Pongo pygmaeus wurmbii ). Female association frequency with both males and females was higher in the Sumatran population, living in more productive habitat. Accordingly, we found that the cost of association, in terms of reduced feeding to moving ratio and increased time being active, is higher in the less sociable Bornean population. Males generally initiated and maintained such costly associations with females, and prolonged associations with males led to increased female fecal cortisol metabolite (FCM) levels at Tuanan, the Bornean population. We conclude that male-maintained associations are an expression of sexual conflict in orangutans, at least at Tuanan. For females, this cost of association may be responsible for the lack of sexual signaling, while needing to confuse paternity. Significance statement Socioecological theory predicts a trade-off between the benefits of sociality and the ecological costs of increased feeding competition. Orangutans’ semi-solitary lifestyle has been attributed to the combination of high association costs and low predation risk. Previous work revealed a positive correlation between association frequencies and habitat productivity, but did not measure the costs of association. In this comparative study, we show that females likely incur costs from involuntary, male-maintained associations, especially when they last for several days and particularly in the population characterized by lower association frequencies. Association maintenance therefore qualifies as another expression of sexual conflict in orangutans, and especially prolonged, male-maintained associations may qualify as an indirect form of sexual coercion. 

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