The antipredator benefits of postural camouflage in peppered moth caterpillars.

Funder: Churchill College, University of Cambridge; doi: http://dx.doi.org/10.13039/501100000742Funder: Projekt DEALCamouflage is the most common form of antipredator defense, and is a textbook example of natural selection. How animals' appearances prevent detection or recognition is well studied, but the role of prey behavior has received much less attention. Here we report a series of experiments with twig-mimicking larvae of the American peppered moth Biston betularia that test the long-held view that prey have evolved postures that enhance their camouflage, and establish how food availability and ambient temperature affect these postures. We found that predators took longer to attack larvae that were resting in a twig-like posture than larvae resting flat against a branch. Larvae that were chilled or food restricted (manipulations intended to energetically stress larvae) adopted a less twig-like posture than larvae that were fed ad libitum. Our findings provide clear evidence that animals gain antipredator benefits from postural camouflage, and suggest that benefits may come at an energetic cost that animals are unwilling or unable to pay under some conditions

Changes in women’s facial skin color over the ovulatory cycle are not detectable by the human visual system

Human ovulation is not advertised, as it is in several primate species, by conspicuous sexual swellings. However, there is increasing evidence that the attractiveness of women’s body odor, voice, and facial appearance peak during the fertile phase of their ovulatory cycle. Cycle effects on facial attractiveness may be underpinned by changes in facial skin color, but it is not clear if skin color varies cyclically in humans or if any changes are detectable. To test these questions we photographed women daily for at least one cycle. Changes in facial skin redness and luminance were then quantified by mapping the digital images to human long, medium, and shortwave visual receptors. We find cyclic variation in skin redness, but not luminance. Redness decreases rapidly after menstrual onset, increases in the days before ovulation, and remains high through the luteal phase. However, we also show that this variation is unlikely to be detectable by the human visual system. We conclude that changes in skin color are not responsible for the effects of the ovulatory cycle on women’s attractiveness

Partner choice, relationship satisfaction, and oral contraception: the congruency hypothesis

Hormonal fluctuation across the menstrual cycle explains temporal variation in women’s judgment of the attractiveness of members of the opposite sex. Use of hormonal contraceptives could therefore influence both initial partner choice and, if contraceptive use subsequently changes, intrapair dynamics. Associations between hormonal contraceptive use and relationship satisfaction may thus be best understood by considering whether current use is congruent with use when relationships formed, rather than by considering current use alone. In the study reported here, we tested this congruency hypothesis in a survey of 365 couples. Controlling for potential confounds (including relationship duration, age, parenthood, and income), we found that congruency in current and previous hormonal contraceptive use, but not current use alone, predicted women’s sexual satisfaction with their partners. Congruency was not associated with women’s nonsexual satisfaction or with the satisfaction of their male partners. Our results provide empirical support for the congruency hypothesis and suggest that women’s sexual satisfaction is influenced by changes in partner preference associated with change in hormonal contraceptive use

Sexual selection on male vocal fundamental frequency in humans and other anthropoids

D.A.P. was supported by a National Institutes of Mental Health T32 MH70343-05 fellowship. J.R.W. was supported by a National Science Foundation predoctoral fellowship.In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency (F0) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F0 sexual dimorphism than any other ape. We also show that low-F0 vocalizations predict perceptions of men’s dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.PostprintPeer reviewe

Facial appearance affects voting decisions

Human groups are unusual among primates in that our leaders are often 5 democratically selected. Many social judgements are made using only facial 6 information and here we examined the potential influence of facial perceptions 7 on leadership elections. We address this possibility using a case study of the 8 2004 US presidential candidates George Bush and John Kerry. We removed 9 recognition effects by applying the difference between their faces to a neutral, 10 unfamiliar face, and then measured how the difference in their facial 11 physiognomies influenced attributions and hypothetical voting decisions. The 12 ‘plus-Bush’ and ‘plus-Kerry’ faces were seen to possess different but 13 potentially valued leadership traits. For voting, preference for face version was 14 context-dependent. Raters preferred the plus-Bush face as a war-time leader 15 and the plus-Kerry face as a peace-time leader. We also examined voting to 16 computer graphic manipulations of masculinity showing that masculine faces 17 were voted for more in war-time and feminine faces in peace-time contexts, 18 suggesting that attitudes to sexual dimorphism in faces play an important role 19 in voting decisions. Both findings demonstrate that voter’s attitudes to the 20 physical appearance of politicians may interact with their perceptions of the 21 current political climate to determine voting behaviour. Such flexible 22 leadership choice may reflect the selection of leaders who are most beneficial 23 to the individuals of a group at a particular time or in a particular situation

Face, body and speech cues independently predict judgments of attractiveness

Research on human attraction frequently makes use of single-modality stimuli such as neutral-expression facial photographs as proxy indicators of an individual’s attractiveness. However, we know little about how judgments of these single-modality stimuli correspond to judgments of stimuli that incorporate multi-modal cues of face, body and speech. In the present study, ratings of attractiveness judged from videos of participants introducing themselves were independently predicted by judgments of the participant’s facial attractiveness (a neutral-expression facial photograph masked to conceal the hairstyle), body attractiveness (a photograph of the upper body), and speech attractiveness (the soundtrack to the video). We also found that ratings of the face, body and speech were positively related to each other. Our results support the assumption that the single-modality stimuli used in much attractiveness research are valid proxy indicators of overall attractiveness in ecologically valid contexts, and complement literature showing cross-modality concordance of trait attractiveness, but also recommend that research relying on assessments of individual attractiveness take account of both visual and vocal attractiveness where possible

Male counter strategies to cyclic shifts

Human female fertility varies over the menstrual cycle. The likelihood that a single act of intercourse will result in conception is greatest in the days preceding ovulation. At this time, women are more attractive and are more driven to enhance their attractiveness. Androphilic women become more interested in men who are not their primary partner, and their preference for physically and behaviorally feminine men decreases. Because men who are women's primary partners risk desertion or (if their partner engages in short-term sexual relationships with other men) investing in biologically unrelated offspring, they have likely experienced selection pressure to deploy counterstrategies that mitigate the effects of female menstrual cycle shifts. These counterstrategies may include changes to a man's sexual desire, his jealousy and mate-guarding behavior, and his propensity to compete with sexual rivals

Investigating the ovulatory cycle: An overview of research and methods

Human female fertility varies over the menstrual cycle. The likelihood that a single act of intercourse will result in conception is greatest in the days preceding ovulation. At this time, women are more attractive and are more driven to enhance their attractiveness. Androphilic women become more interested in men who are not their primary partner, and their preference for physically and behaviorally feminine men decreases. Because men who are women's primary partners risk desertion or (if their partner engages in short-term sexual relationships with other men) investing in biologically unrelated offspring, they have likely experienced selection pressure to deploy counterstrategies that mitigate the effects of female menstrual cycle shifts. These counterstrategies may include changes to a man's sexual desire, his jealousy and mate-guarding behavior, and his propensity to compete with sexual rivals