Corri Waitt

Evidence from rhesus macaques suggests that male coloration plays a role in female primate mate choice

Male animals of many species use conspicuous coloration to attract mates. Among mammals, primates possess the most brilliant secondary sexual coloration. However, whether colour plays a part in primate female mate choice remains unknown. Adult male rhesus macaques undergo a hormonally regulated increased reddening of facial and anogenital skin during their mating season. We experimentally investigated whether red male facial coloration is preferred by simultaneously presenting female rhesus macaques (n = 6) with computer-manipulated pale and red versions of 24 different male faces. The duration and direction of gaze were measured to discern visual preferences. Females exhibited preferences for the red versions of male faces. It is proposed that male coloration might provide a cue to male quality.

Symmetry Is Related to Sexual Dimorphism in Faces: Data Across Culture and Species

Background Many animals both display and assess multiple signals. Two prominently studied traits are symmetry and sexual dimorphism, which, for many animals, are proposed cues to heritable fitness benefits. These traits are associated with other potential benefits, such as fertility. In humans, the face has been extensively studied in terms of attractiveness. Faces have the potential to be advertisements of mate quality and both symmetry and sexual dimorphism have been linked to the attractiveness of human face shape. Methodology/Principal Findings Here we show that measurements of symmetry and sexual dimorphism from faces are related in humans, both in Europeans and African hunter-gatherers, and in a non-human primate. Using human judges, symmetry measurements were also related to perceived sexual dimorphism. In all samples, symmetric males had more masculine facial proportions and symmetric females had more feminine facial proportions. Conclusions/Significance Our findings support the claim that sexual dimorphism and symmetry in faces are signals advertising quality by providing evidence that there must be a biological mechanism linking the two traits during development. Such data also suggests that the signalling properties of faces are universal across human populations and are potentially phylogenetically old in primates.

What time is feeding?: How delays and anticipation of feeding schedules affect stump-tailed macaque behavior

Abstract Everyday animal care routines are essential to an animal’s physical well-being, but the effects of husbandry routines on the animals’ psychological well-being are not often considered. The scheduling of animal care routines may have an important impact on how they are perceived by the animals involved. It was the objective of this study to assess how anticipation and delays of feeding routines impacts captive primates, in this study stump-tailed macaques (Macaca arctoides). To determine how anticipation of food delivery affected behavior, this study compared behavior when feeding routines were carried out earlier to when feeding took place on-schedule. Secondly, the impact of delays of feeding routines were investigated by comparing behavior when feeding routines occurred later than usual to when they took place on time. Results indicate that anticipation of feeding routines had a considerable negative impact on behavior. In the times when animals were awaiting to be fed, rates of self-directed behavior, inactivity, vocalization and abnormal behaviors all increased significantly. When feeding was delayed past the mean routine time, these behavioral patterns were prolonged. It was concluded that feeding animals at a regular time, each day does not truly make routines predictable. Delays in the timing of these events make these events even more unpredictable, and thus all the more stressful. The implications of these results in relation to animal management are discussed.

Preferences for Symmetry in Conspecific Facial Shape Among Macaca mulatta

In human males and females, bilateral symmetry of facial shape influences assessments of attractiveness. It is possible, however, that other primate species also possess preferences for conspecific facial symmetry. To assess this experimentally, we presented 13 adult rhesus macaques (8 females, 5 males) with computer-manipulated images of symmetrical and asymmetrical versions of opposite-sexed conspecific faces. We utilized looking behavior to assess visual preferences for these factors. We found significant preferences for symmetry, raising the possibility that human preferences for facial symmetry are more deeply rooted in our evolutionary history than previously realized. Our results also have implications for the use of facial shape as a mechanism for attractiveness appraisals across the Primates.

The effects of caretaker-primate relationships on primates in the laboratory.

As contact with caretakers is likely to make up the majority of human-primate interactions in laboratories, caretakers represent an important influence in the lives of captive primates. The aim of this study was to determine how caretaker-primate relationships affected the behavior of primates in the laboratory. We examined whether stump-tailed macaques (Macaca arctoides) who were evaluated by caretakers as being either friendly or unfriendly differed in the quality and quantity of interactions with their caretakers during husbandry procedures and in their behavior at times of high and low levels of caretaker activity. Results revealed that animals who had friendly relationships with caretakers were less disturbed by routine husbandry procedures, approached caretakers more often, and were willing to accept food offered by caretakers compared with animals considered unfriendly toward their caretakers. The study concluded that the quality of the primate-caretaker relationship may have an important impact on behavior and may have implications for the well-being of animals and caretakers, as both can benefit from positive feedback from one another.

Females pay attention to female secondary sexual color:An experimental study in Macaca mulatta

Researchers have long considered the color of female sexual skin to play a role in attracting or inciting competition among males, or both; however, females may also use color in intrasexual communication. To assess this possibility, we examined whether variation in same-sex sexual skin color is salient to female rhesus macaques (Macaca mulatta). We exposed adult females to computerized images of conspecific female faces and hindquarters manipulated for color (red vs. non-red), within the natural range of color variation. Females visually attended more to both reddened faces and hindquarters over the non-red counterparts. We conclude that female color might be biologically meaningful to other females.

Pregnancy coloration in macaques may act as a warning signal to reduce antagonism by conspecifics

Instances of bright, hormonally induced coloration among females during gestation have been reported in a few reptile and primate genera. Gravid coloration in lizards has been linked to female aggression but the influence of color changes associated with pregnancy has not yet been experimentally pursued for primates. As a first step to determine whether the crimson to magenta hues common to pregnancy coloration in rhesus macaques (Macaca mulatta) contains information, to which conspecifics of either sex attend, we evaluated whether male and female rhesus macaques discriminate between pregnant and non-pregnant female faces. To these ends, we presented 19 adult rhesus macaques with color-manipulated digital images of female faces where pregnancy coloration was present or absent, and measured visual attention and behavioral reactions. Males were significantly more attentive to female faces with pregnancy coloration over those without pregnancy coloration. Both sexes engaged in higher levels of appeasement behavior toward stimulus with pregnancy coloration, and males showing signs of anxiety did so exclusively when exposed to faces with pregnancy coloration. Our results suggest that pregnancy coloration might be an attention grabbing stimulus to males and a warning stimulus to both male and female rhesus macaques. The findings provide a comparative perspective on the use of color in intra-specific communication, and suggest similarity in female similarity in signalling properties in distantly related taxa.

Do females pay attention to secondary sexual coloration in vervet monkeys (Chlorocebus aethiops)

Several primate species show sexual dichromatism with males displaying conspicuous coloration of the pelage or skin. Studies of scrotal coloration in male vervet monkeys (Chlorocebus aethiops) suggest that it is an important intrasexual signal, with relatively dark, colourful males dominating paler males. To date, no studies have examined the influence of male colour on intersexual social interactions in vervet monkeys. The primary goal of the present study was to evaluate whether female vervet monkeys attend to male coloration. We experimentally introduced females, housed with either “pale” or “dark” males, to stimulus males whose scrota were pale, dark, or pale but painted to look dark. Overall, during introductions, females did not differ in time spent directing affiliative behaviour toward pale, dark, and painted males; however, females, permanently housed with dark males, spent significantly more time directing affiliative behaviour toward pale than painted males. When the stimulus male was pale, affiliative exchanges between males and females were longer than when the stimulus male was painted. Home male colour was not related to female-initiated aggression. Home male colour was also not related to male-initiated aggression, although painted stimulus males were more likely to initiate aggression than pale stimulus males. These findings lead us to conclude that females pay attention to male coloration, but do not bias their interactions toward males solely on the basis of natural male coloration.

An experimental examination of female responses to infant face coloration in rhesus macaques

In many primates, infants possess distinctive coloration that changes as a function of age. This colour is thought to serve the purpose of eliciting caretaking behaviour from the mother as well as other conspecifics. The present study investigated the responses of adult female rhesus macaques (Macaca mulatta) to pictures of infant faces in relation to infant age and facial coloration. Study animals were shown digitized images of neonates and 5-6-month-old infants displaying either unaltered facial colour, pink neonatal colour, or novel (green) facial colour. While infant and neonate faces of all colours elicited the attention of adult females, pink neonatal facial coloration did not appear to be especially attractive to subjects in contrast with the findings from an earlier study [Higley, J.D., Hopkins, W.D., Hirsch, R.M. Marra, L.M. Suomi S.J., 1987. Preferences of female rhesus monkeys (Macaca mulatta) for infantile coloration. Dev. Psychobiol. 20, 7-18]. The results suggest that infant facial colour is not particularly important in mediating infant attractiveness to rhesus macaque females as previously suggested or that other infantile facial characteristics might be more important than colour in eliciting caretaking behaviours amongst females.

Improving the Welfare of Captive Macaques (Macaca sp.) Through the Use of Water as Enrichment

This review evaluates the use of water as a tool for enriching the environments of macaques (Macaca sp.) in captivity. Many macaque species are known to swim and forage in water in the wild, and in-situ reports suggest that access to water promotes activity and cultural behavior. Yet, there is a relative dearth of information on water enrichment, covering only a small number of macaque species in both laboratory and zoo settings. Previous studies in captivity report high levels of usage of water enrichment as well as further behavioral benefits, including increases in play, exploratory behavior, and tool use. Subsequently, there is a clear need for more research on the potential benefits of water enrichment for both macaques and other primate species, especially given that small water troughs and pools provide an inexpensive method for enriching nonhuman primate lives in captivity.