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1. Orangutan Socio-Sexual Behavior and Sexual Conflict: Insights for Human Evolution

   Knott, CD (January 2021, 2021 European Evolution and Human Behaviour Association Meeting)

   null (Ed.)

   In this talk I reveal how recent research on great ape behavior and physiology provides new insights into the similarities we share with our closest relatives. In particular, I focus on my long-term research studying wild orangutans in Gunung Palung National Park, Indonesia for over 25 years. Orangutans are known for one of the highest rates of sexual coercion, through forced copulation, of any animal. This is coupled with another intriguing phenomenon of having two male morphs, a rare type of male bi-maturism. Females share crucial features of reproductive physiology in common with humans, such as concealed ovulation and menstrual cycle length. In this talk I explore the complexity of male and female reproductive decisions in wild orangutans and the ways that these reveal insights into the evolution of human mating systems. This includes new research from my team on the development of socio-sexual behavior in adolescent females and how the threat of forced copulation, as well possible infanticide risk, impacts female behavior and ranging patterns. I also demonstrate the success of strategies employed by females to avoid undesired sires. These results reveal that, despite high rates of forced copulation, female choice is an important feature of orangutan mating patterns. I also discuss why sexual coercion is so prevalent in orangutans and how this type of sexual selection may be much more common across animals than often recognized. I point to the need for considering comparative data on sexual conflict as we consider the evolution of human mating patterns. 

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2. Cross-sexual Transfer Revisited

   https://doi.org/10.1093/icb/icad021  

   Anderson, Andrew P.; Falk, Jay Jinsing (May 2023, Integrative And Comparative Biology)

   Abstract In her influential book “Developmental Plasticity and Evolution,” Mary Jane West-Eberhard introduced the concept of cross-sexual transfer, where traits expressed in one sex in an ancestral species become expressed in the other sex. Despite its potential ubiquity, we find that cross-sexual transfer has been under-studied and under-cited in the literature, with only a few experimental papers that have invoked the concept. Here, we aim to reintroduce cross-sexual transfer as a powerful framework for explaining sex variation and highlight its relevance in current studies on the evolution of sexual heteromorphism (different means or modes in trait values between the sexes). We discuss several exemplary studies of cross-sexual transfer that have been published in the past two decades, further building on West-Eberhard’s extensive review. We emphasize two scenarios as potential avenues of study, within-sex polymorphic and sex-role reversed species, and discuss the evolutionary and adaptive implications. Lastly, we propose future questions to expand our understanding of cross-sexual transfer, from nonhormonal mechanisms to the identification of broad taxonomic patterns. As evolutionary biologists increasingly recognize the nonbinary and often continuous nature of sexual heteromorphism, the cross-sexual framework has important utility for generating novel insights and perspectives on the evolution of sexual phenotypes across diverse taxa. 

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3. Interspecific allometry for sexual shape dimorphism: Macroevolution of multivariate sexual phenotypes with application to Rensch's rule

   https://doi.org/10.1111/evo.14049  

   Adams, Dean_C; Glynne, Elizabeth; Kaliontzopoulou, Antigoni (July 2020, Evolution)
4. Evolution: The biochemistry of honest sexual signaling

   https://doi.org/10.1016/j.cub.2022.09.001  

   Hill, Geoffrey E. (October 2022, Current Biology)
5. Sexual repurposing of juvenile aposematism in locusts

   https://doi.org/10.1073/pnas.2200759119  

   Cullen, Darron A.; Sword, Gregory A.; Rosenthal, Gil G.; Simpson, Stephen J.; Dekempeneer, Elfie; Hertog, Maarten L.; Nicolaï, Bart M.; Caes, Robbe; Mannaerts, Lisa; Vanden Broeck, Jozef (August 2022, Proceedings of the National Academy of Sciences)

   Adaptive plasticity requires an integrated suite of functional responses to environmental variation, which can include social communication across life stages. Desert locusts ( Schistocerca gregaria ) exhibit an extreme example of phenotypic plasticity called phase polyphenism, in which a suite of behavioral and morphological traits differ according to local population density. Male and female juveniles developing at low population densities exhibit green- or sand-colored background-matching camouflage, while at high densities they show contrasting yellow and black aposematic patterning that deters predators. The predominant background colors of these phenotypes (green/sand/yellow) all depend on expression of the carotenoid-binding “Yellow Protein” ( YP ). Gregarious (high-density) adults of both sexes are initially pinkish, before a YP -mediated yellowing reoccurs upon sexual maturation. Yellow color is especially prominent in gregarious males, but the reason for this difference has been unknown since phase polyphenism was first described in 1921. Here, we use RNA interference to show that gregarious male yellowing acts as an intrasexual warning signal, which forms a multimodal signal with the antiaphrodisiac pheromone phenylacetonitrile (PAN) to prevent mistaken sexual harassment from other males during scramble mating in a swarm. Socially mediated reexpression of YP thus adaptively repurposes a juvenile signal that deters predators into an adult signal that deters undesirable mates. These findings reveal a previously underappreciated sexual dimension to locust phase polyphenism, and promote locusts as a model for investigating the relative contributions of natural versus sexual selection in the evolution of phenotypic plasticity. 

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