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- ItemDo monkeys use sex toys? Evidence of stone tool-assisted masturbation in free-ranging long-tailed macaques(Wiley, 2022) Cenni, Camilla; Christie, Jessica B. A.; Van der Pant, Yanni; Gunst, Noëlle; Vasey, Paul L.; Wandia, Nengah; Leca, Jean-BaptisteRecent reports on tool use in nonforaging contexts have led researchers to reconsider the proximate drivers of instrumental object manipulation. In this study, we explore the physiological and behavioral correlates of two stone-directed and seemingly playful actions, the repetitive tapping and rubbing of stones onto the genital and inguinal area, respectively, that may have been co-opted into self-directed tool-assisted masturbation in long-tailed macaques (i.e., “Sex Toy” hypothesis). We predicted that genital and inguinal stone-tapping and rubbing would be more closely temporally associated with physiological responses (e.g., estrus in females, penile erection in males) and behavior patterns (e.g., sexual mounts and other mating interactions) that are sexually motivated than other stone-directed play. We also predicted that the stones selected to perform genital and inguinal stone-tapping and rubbing actions would be less variable in number, size, and texture than the stones typically used during other stone-directed playful actions. Overall, our data partly supported the “Sex Toy” hypothesis indicating that stone-directed tapping and rubbing onto the genital and inguinal area are sexually motivated behaviors. Our research suggests that instrumental behaviors of questionably adaptive value may be maintained over evolutionary time through pleasurable/self-rewarding mechanisms, such as those underlying playful and sexual activities.
- ItemSexual adaptation: is female-male mounting a supernormal courtship display in Japanese macaques?(Brill, 2022) Gunst, Noëlle; Leca, Jean-Baptiste; Vasey, Paul L.We analysed heterosexual consortships in a free-ranging group of Japanese macaques in which adult females routinely perform female-to-male mounting (FMM). We tested whether FMM is more efficient (i.e., a “supernormal courtship” behavioral pattern) than species-typical female-to-male sexual solicitations (FMSS) at prompting subsequent male-to-female mounts (MFM). In a context of high femalefemale competition for male mates, we found that (1) FMM functioned to focus the male consort partner’s attention as efficiently as FMSS and prevented him from moving away, and (2) FMM was more efficient than species-typical FMSS at expediting MFM (i.e., the most fitness-enhancing sexual behavior of a mating sequence). We concluded that FMM could be considered a supernormal courtship behavioral pattern in adult female Japanese macaques. This population-specific sexual adaptation may result from a combination of favorable socio-demographic conditions. This study has implications for the evolutionary history of non-conceptive mounting patterns in Japanese macaques and non-conceptive sexuality in humans.
- ItemWhen males have females on their backs: male's tolerance, solicitation, and use of female-male mounting in Japanese macaques(Wiley, 2022) Gunst, Noëlle; Leca, Jean-Baptiste; Vasey, Paul L.Previous research on Japanese macaques has shown that female-to-male mounting (FMM) is performed by some females as an exaggerated form of sexual solicitation that may occur in the context of high female competition for male mates. This supernormal courtship behavior functions to prompt subsequent male-to-female mounting. In this report, we focused on the male consort partners’ responses to FMM. We studied a free-ranging population of Japanese macaques at Arashiyama, Japan, in which FMM is frequent and prevalent. We analyzed 240 consortships involving 31 females and 19 males. We tested three hypotheses regarding male’s tolerance, solicitation, and use of FMM. First, we found that FMM was tolerated by male mountees who were no more likely to aggress their female partners during a short time window around a FMM, than they were during the rest of the consortship period. Second, we showed that FMM could be triggered by male recipients, via explicit male-to-female sexual solicitations. Third, we found that some males may utilize FMM in a quest for their own sexual stimulation, which sometimes culminated in masturbation by the male during FMM. Our findings indicate that male partners facilitate the expression of FMM both passively (via their tolerance) and actively (via their solicitation). In addition, FMM appears to enhance the sexual arousal of male partners during consortships. We argued that, for females to have expanded their repertoire of sexual solicitations by adopting FMM, male mates must have played a role in the evolutionary origins and maintenance of this non-conceptive, but intense and powerful female mating tactic.
- ItemAcquisition of object-robbing and object/food-bartering behaviours: a culturally maintained token economy in free-ranging long-tailed macaques(The Royal Society Publishing, 2021) Leca, Jean-Baptiste; Gunst, Noëlle; Gardiner, Matthew; Wandia, I. NengahThe token exchange paradigm shows that monkeys and great apes are able to use objects as symbolic tools to request specific food rewards. Such studies provide insights into the cognitive underpinnings of economic behaviour in non-human primates. However, the ecological validity of these laboratory-based experimental situations tends to be limited. Our field research aims to address the need for a more ecologically valid primate model of trading systems in humans. Around the Uluwatu Temple in Bali, Indonesia, a large free-ranging population of long-tailed macaques spontaneously and routinely engage in token-mediated bartering interactions with humans. These interactions occur in two phases: after stealing inedible and more or less valuable objects from humans, the macaques appear to use them as tokens, by returning them to humans in exchange for food. Our field observational and experimental data showed (i) age differences in robbing/bartering success, indicative of experiential learning, and (ii) clear behavioural associations between value-based token possession and quantity or quality of food rewards rejected and accepted by subadult and adult monkeys, suggestive of robbing/bartering payoff maximization and economic decision-making. This population-specific, prevalent, cross-generational, learned and socially influenced practice may be the first example of a culturally maintained token economy in free-ranging animals.
- ItemBehavior systems approach to object play: stone handling repertoire as a measure of propensity for complex foraging and percussive tool use in the genus Macaca(SciKnow Publications, 2017) Pelletier, Amanda N.; Kaufmann, Tatjana; Mohak, Sidhesh; Milan, Riane; Nahallage, Charmalie A. D.; Huffman, Michael A.; Gunst, Noëlle; Rompis, Aida; Wandia, I Nengah; Arta Purta, I Gusti A.; Pellis, Sergio M.; Leca, Jean-BaptisteStone handling (SH), has been identified in four closely related primate species of the Macaca genus. We provide the first ethogram of SH in long-tailed macaques (Macaca fascicularis), a primate species known to use stones for extractive foraging. A total of 62.7 hrs of video recorded data were scored from a population of Balinese long-tailed macaques living in Ubud, Bali, Indonesia, and a total of 36 stone handling patterns were identified. Behavior discovery curves were generated and showed that the minimum threshold of completeness was exceeded for the SH repertoire in this group. A “foraging substitute” hypothesis for the expression of SH was proposed, suggesting that SH consists of performing foraging-like actions on non-edible objects. We used a “behavior systems” framework to test this prediction, finding that all 36 stone handling patterns could be reliably categorized in a foraging behavior system, supporting the hypothesis that stone handling can be considered pseudo-foraging behavior. Our “behavior systems” approach will serve as a foundation for the future testing of the motivational basis of stone handling. Additionally, a comparison of 39 stone handling patterns performed by three macaque species (M. fascicularis, M. fuscata and M. mulatta) showed overlapping behavioral propensities to manipulate stones; however, the differences suggest that long-tailed macaques might be more prone to use stones as percussive tools in a foraging context. This work could offer insights into the development and evolution of complex activities such as percussive stone tool use in early humans.