skip to main content

Explore Research Products in the NSF-PAR

Title: Orangutan Socio-Sexual Behavior and Sexual Conflict: Insights for Human Evolution
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.  more » « less
Award ID(s):
1638823
NSF-PAR ID:
10291765
Author(s) / Creator(s):
Date Published:
Journal Name:
2021 European Evolution and Human Behaviour Association Meeting
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al ( , 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. 
    more » « less
  2. ; ( , Science)
    BACKGROUND Charles Darwin’s  Descent of Man, and Selection in Relation to Sex  tackled the two main controversies arising from the Origin of Species:  the evolution of humans from animal ancestors and the evolution of sexual ornaments. Most of the book focuses on the latter, Darwin’s theory of sexual selection. Research since supports his conjecture that songs, perfumes, and intricate dances evolve because they help secure mating partners. Evidence is overwhelming for a primary role of both male and female mate choice in sexual selection—not only through premating courtship but also through intimate interactions during and long after mating. But what makes one prospective mate more enticing than another? Darwin, shaped by misogyny and sexual prudery, invoked a “taste for the beautiful” without speculating on the origin of the “taste.” How to explain when the “final marriage ceremony” is between two rams? What of oral sex in bats, cloacal rubbing in bonobos, or the sexual spectrum in humans, all observable in Darwin’s time? By explaining desire through the lens of those male traits that caught his eyes and those of his gender and culture, Darwin elided these data in his theory of sexual evolution. Work since Darwin has focused on how traits and preferences coevolve. Preferences can evolve even if attractive signals only predict offspring attractiveness, but most attention has gone to the intuitive but tenuous premise that mating with gorgeous partners yields vigorous offspring. By focusing on those aspects of mating preferences that coevolve with male traits, many of Darwin’s influential followers have followed the same narrow path. The sexual selection debate in the 1980s was framed as “good genes versus runaway”: Do preferences coevolve with traits because traits predict genetic benefits, or simply because they are beautiful? To the broader world this is still the conversation. ADVANCES Even as they evolve toward ever-more-beautiful signals and healthier offspring, mate-choice mechanisms and courter traits are locked in an arms race of coercion and resistance, persuasion and skepticism. Traits favored by sexual selection often do so at the expense of chooser fitness, creating sexual conflict. Choosers then evolve preferences in response to the costs imposed by courters. Often, though, the current traits of courters tell us little about how preferences arise. Sensory systems are often tuned to nonsexual cues like food, favoring mating signals resembling those cues. And preferences can emerge simply from selection on choosing conspecifics. Sexual selection can therefore arise from chooser biases that have nothing to do with ornaments. Choice may occur before mating, as Darwin emphasized, but individuals mate multiple times and bias fertilization and offspring care toward favored partners. Mate choice can thus occur in myriad ways after mating, through behavioral, morphological, and physiological mechanisms. Like other biological traits, mating preferences vary among individuals and species along multiple dimensions. Some of this is likely adaptive, as different individuals will have different optimal mates. Indeed, mate choice may be more about choosing compatible partners than picking the “best” mate in the absolute sense. Compatibility-based choice can drive or reinforce genetic divergence and lead to speciation. The mechanisms underlying the “taste for the beautiful” determine whether mate choice accelerates or inhibits reproductive isolation. If preferences are learned from parents, or covary with ecological differences like the sensory environment, then choice can promote genetic divergence. If everyone shares preferences for attractive ornaments, then choice promotes gene flow between lineages. OUTLOOK Two major trends continue to shift the emphasis away from male “beauty” and toward how and why individuals make sexual choices. The first integrates neuroscience, genomics, and physiology. We need not limit ourselves to the feathers and dances that dazzled Darwin, which gives us a vastly richer picture of mate choice. The second is that despite persistent structural inequities in academia, a broader range of people study a broader range of questions. This new focus confirms Darwin’s insight that mate choice makes a primary contribution to sexual selection, but suggests that sexual selection is often tangential to mate choice. This conclusion challenges a persistent belief with sinister roots, whereby mate choice is all about male ornaments. Under this view, females evolve to prefer handsome males who provide healthy offspring, or alternatively, to express flighty whims for arbitrary traits. But mate-choice mechanisms also evolve for a host of other reasons Understanding mate choice mechanisms is key to understanding how sexual decisions underlie speciation and adaptation to environmental change. New theory and technology allow us to explicitly connect decision-making mechanisms with their evolutionary consequences. A century and a half after Darwin, we can shift our focus to females and males as choosers, rather than the gaudy by-products of mate choice. Mate choice mechanisms across domains of life. Sensory periphery for stimulus detection (yellow), brain for perceptual integration and evaluation (orange), and reproductive structures for postmating choice among pollen or sperm (teal). ILLUSTRATION: KELLIE HOLOSKI/ SCIENCE 
    more » « less
  3. ; ; ( , American Journal of Primatology)
    Abstract

    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.

     
    more » « less
  4. ; ; ( , 6th Annual Meeting of the Northeastern Evolutionary Primatologists)
    null (Ed.)
    Due to extreme incongruence in parental investment, the potential for sexual conflict in orangutan reproductive strategies is high. Female orangutans prefer flanged males, but with intense male-male competition and sexual coercion, it is unclear how females are able to exert choice. We hypothesized that female orangutans use initiation and maintenance of associations with preferred males as a mechanism of female choice. We used encounter rates and behavioral measures of proximity maintenance to distinguish between the role of female choice and male coercion in male-female associations in Gunung Palung National Park, West Kalimantan, Indonesia. From May 2018-April 2019, we collected data on initiation, termination, and proximity maintenance during associations between males and cycling females (females without dependent offspring or with offspring over 6 years old). Encounters between cycling females and flanged males were more likely to be female-initiated (83.3%), while encounters with unflanged males were more likely to be male-initiated (80%) (N=16, p=0.035, Fisher’s exact test). Additionally, the Brown Index indicates significantly more female proximity maintenance when cycling females associated with flanged males than unflanged males (N=33, W = 198.5, p= 0.012). However, using long-term data on male-female associations, we found that dyads of flanged males and females were less likely to encounter other males compared to dyads of unflanged males and females (N=542, χ2= 3.3051, df=1, p=0.035). This indicates that flanged males may also use associations to mate guard females. These data indicate that there are behavioral manifestations of both female choice and male coercion in orangutan associations. Funders: NSF (DGE-1247312, BCS-1638823, BCS-0936199), Boston University, Leakey Foundation, Disney Conservation Fund, and US Fish and Wildlife Service (F18AP00898) 
    more » « less
  5. ; ; ( , 90th Annual Meeting of the American Association of Physical Anthropologists)
    null (Ed.)
    Due to extreme incongruence in parental investment, the potential for sexual conflict in orangutan reproductive strategies is high. Female orangutans prefer flanged males, but with intense male-male competition and sexual coercion, it is unclear how females are able to exert choice. We hypothesized that female orangutans use initiation and maintenance of associations with preferred males as a mechanism of female choice. We used encounter rates and behavioral measures of proximity maintenance to distinguish between the role of female choice and male coercion in male-female associations in Gunung Palung National Park, West Kalimantan, Indonesia. From May 2018-April 2019, we collected data on initiation, termination, and proximity maintenance during associations between males and cycling females (females without dependent offspring or with offspring over 6 years old). Encounters between cycling females and flanged males were more likely to be female-initiated (83.3%), while encounters with unflanged males were more likely to be male-initiated (80%) (N=16, p=0.035, Fisher’s exact test). Additionally, the Brown Index indicates significantly more female proximity maintenance when cycling females associated with flanged males than unflanged males (N=33, W = 198.5, p= 0.012). However, using long-term data on male-female associations, we found that dyads of flanged males and females were less likely to encounter other males compared to dyads of unflanged males and females (N=542, χ2= 3.3051, df=1, p=0.035). This indicates that flanged males may also use associations to mate guard females. These data indicate that there are behavioral manifestations of both female choice and male coercion in orangutan associations. Funders: NSF (DGE-1247312, BCS-1638823, BCS-0936199), Boston University, Leakey Foundation, Disney Conservation Fund, and US Fish and Wildlife Service (F18AP00898) 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email