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Abstract Background Previous research has shown that the type and duration of erotic material that men have access to during masturbation can influence semen parameters. To our knowledge, the use of virtual reality (VR) headsets to present erotica has not previously been studied. We reasoned that, because VR can provide a more immersive experience to the user, semen parameters of masturbatory ejaculates may be altered. Methods This study had a balanced and randomized controlled cross-over within-subjects design. 504 ejaculates were collected from 63 sperm donors at 4 locations in Denmark. During masturbation each donor was instructed to observe erotic material either on a touch screen monitor or using a VR headset. The order of each pair of within-subject treatments was randomized by the throw of a dice. Anonymized data were analysed with linear mixed and piecewise structural equation models. Results Both abstinence period and VR-use influenced the total number of motile spermatozoa ejaculated. For short abstinence periods, VR-use increased the number of motile sperm in the ejaculate. However, the difference between VR and non-VR ejaculates decreased as abstinence period increased such that there was no difference at the mean abstinence period of 58 h. For longer abstinence periods, total motile sperm counts were lower, on average, when men used VR compared to those that did not. Conclusion The use of VR headsets to view erotica had a strong positive effect on the number of motile sperm in an ejaculate when the donor’s abstinence time was short (

To date, the majority of authors on scientific publications have been men. While much of this gender bias can be explained by historic sexism and discrimination, there is concern that women may still be disadvantaged by the peer review process if reviewers’ biases lead them to reject publications with female authors more often. One potential solution to this perceived gender bias in the reviewing process is for journals to adopt double-blind reviews whereby neither the authors nor the reviewers are aware of each other’s identity and gender. To test the efficacy of double-blind reviews in one behavioral ecology journal (Behavioral Ecology, BE), we assigned gender to every authorship of every paper published for 2010–2018 in that journal compared to four other journals with single-blind reviews but similar subject matter and impact factors. While female authorships comprised only 35% of the total in all journals, the double-blind journal (BE) did not have more female authorships than its single-blind counterparts. Interestingly, the incidence of female authorship is higher at behavioral ecology journals (BE and Behavioral Ecology and Sociobiology) than in the ornithology journals (Auk, Condor, Ibis) for papers on all topics as well as those on birds. These analyses suggest that double-blind review does not currently increase the incidence of female authorship in the journals studied here. We conclude, at least for these journals, that double-blind review no longer benefits female authors and we discuss the pros and cons of the double-blind reviewing process based on our findings.

Courtship displays may serve as signals of the quality of motor performance, but little is known about the underlying biomechanics that determines both their signal content and costs. Peacocks (Pavo cristatus) perform a complex, multimodal "train-rattling" display in which they court females by vibrating the iridescent feathers in their elaborate train ornament. Here we study how feather biomechanics influences the performance of this display using a combination of field recordings and laboratory experiments. Using high-speed video, we find that train-rattling peacocks stridulate their tail feathers against the train at 25.6 Hz, on average, generating a broadband, pulsating mechanical sound at that frequency. Laboratory measurements demonstrate that arrays of peacock tail and train feathers have a broad resonant peak in their vibrational spectra at the range of frequencies used for train-rattling during the display, and the motion of feathers is just as expected for feathers shaking near resonance. This indicates that peacocks are able to drive feather vibrations energetically efficiently over a relatively broad range of frequencies, enabling them to modulate the feather vibration frequency of their displays. Using our field data, we show that peacocks with longer trains use slightly higher vibration frequencies on average, even though longer train feathers are heavier and have lower resonant frequencies. Based on these results, we propose hypotheses for future studies of the function and energetics of this display that ask why its dynamic elements might attract and maintain female attention. Finally, we demonstrate how the mechanical structure of the train feathers affects the peacock's visual display by allowing the colorful iridescent eyespots-which strongly influence female mate choice-to remain nearly stationary against a dynamic iridescent background.

We examined sex allocation patterns in island and mainland populations of cooperatively breeding white-winged fairy-wrens. The marked differences in social structure between island and mainland populations, in addition to dramatic plumage variation among males both within and between populations, provided a unique situation in which we could investigate different predictions from sex allocation theory in a single species. First, we test the repayment (local resource enhancement) hypothesis by asking whether females biased offspring sex ratios in relation to the assistance they derived from helpers. Second, we test the male quality (attractiveness) hypothesis, which suggests that females mated to attractive high-quality males should bias offspring sex ratios in favor of males. Finally, we test the idea that females in good condition should bias offspring sex ratios toward males because they are able to allocate more resources to offspring, whereas females in poor condition should have increased benefits from producing more female offspring (Trivers-Willard hypothesis). We used molecular sexing techniques to assess total offspring sex ratios of 86 breeding pairs over 2 years. Both offspring and first brood sex ratios were correlated with the pair-male''s body condition such that females increased the proportion of males in their brood in relation to the body condition (mass corrected for body size) of their social partner. This relation was both significant and remarkably similar in both years of our study and in both island and mainland populations. Although confidence of paternity can be low in this and other fairy-wren species, we show how this finding might be consistent with the male quality (attractiveness) hypothesis with respect to male condition. There was no support for the repayment hypothesis; the presence of helpers had no effect on offspring sex ratios. There was weak support for both the male quality (attractiveness) hypothesis with respect to plumage color and the maternal condition hypothesis, but their influence on offspring sex ratios was negligible after controlling for the effects of pair-male condition. [ABSTRACT FROM AUTHOR]

The size of achromatic (black, white, gray) plumage patches serves as a male status signal in many species of birds, but variation in the colors of these patches has received little attention. We assessed the relation between achromatic plumage reflectance, dominance rank, body condition, and reproductive success in male black-capped chickadees, Poecile atricapillus. We measured plumage reflectance for five body regions of 40 male chickadees in late winter and monitored these males throughout the following breeding season to determine whether they survived to breed, whether they successfully paired, whether their partner laid eggs, and both their apparent and realized reproductive success. As expected from past studies, a male's dominance rank significantly predicted whether his partner laid eggs. However, only achromatic plumage reflectance significantly predicted other measures of male reproductive performance. Among males who fledged at least one offspring, both the brightness of white plumage regions and the UV-chroma of melanin-based plumage regions were significant predictors of the proportion of within-pair young in their nests. When we consider all males we measured, assigning zero values to males who failed to sire any offspring, the UV-chroma of melanin-based plumage regions was a significant predictor of realized reproductive success. Bib size was also related to male realized reproductive success. Our findings suggest that individual variation in achromatic plumage may play an important role in sexual signaling in chickadees. [ABSTRACT FROM AUTHOR]

We investigated the mating patterns in 22 breeding pairs of wild American goldfinches ( Carduelis tristis) with respect to their body size, condition, and carotenoid-based, yellow plumage colour. Using reflectance spectrometry, we objectively quantified plumage colours across the bird-visible wavelengths, revealing a unexpected UV peak in the reflectance spectrum from yellow feathers. We summarized our colour measurements using a principal components analysis to create a single variable, carotenoid PC1, that represents the intensity of this carotenoid-based yellow colour, a measure of phenotypic quality in this species. We found no evidence of assortative mating with respect to measures of body size or condition but there was positive assortative mating by carotenoid PC1, such that the yellow plumage colours of males and females were significantly correlated within pairs. We argue that the yellow carotenoid coloration of goldfinches may be important in mutual mate choice and, thus, that sexual selection in this species may act upon female ornamentation, as well as the more obvious plumage signals of males. Because assortative mating results in an increase in genetic variance, we suggest that this might be a mechanism that maintains variance in ornamental traits in spite of the variance-eroding effects of sexual selection. [ABSTRACT FROM AUTHOR]

Much attention has been devoted to understanding the evolution of elaborate male ornaments and how they may signal male quality. However, the evolution of multicomponent sexual signals remains poorly understood, and past research on this type of signaling has been largely theoretical. Satin bowerbirds, Ptilonorhynchus violaceus, are polygynous, are sexually dichromatic, and construct sexually selected display structures (bowers): a model system for investigating the evolution and signal function of multiple sexual signals. We studied the interrelationship between bower features, plumage coloration, and indicators of male quality in this species. To do this, we located the bowers of male satin bowerbirds in rainforest in Queensland, Australia, and quantified bower quality. We captured the male bower owners and used reflectance spectrometry to objectively measure the plumage coloration of several body regions. We measured various indicators of male health and condition, including the intensity of infection from ectoparasites and blood parasites. Bower quality and male ultraviolet plumage coloration were significantly correlated. By using multiple regression analyses, we show that bower quality predicts ectoparasite load and body size, whereas ultraviolet plumage coloration predicts the intensity of infection from blood parasites, feather growth rate, and body size. Our findings support the multiple messages hypothesis of multicomponent signals: Female satin bowerbirds should assess both male and bower features to choose the highest quality mates. [ABSTRACT FROM AUTHOR]

We compared pairs of closely related taxa of cichlid fishes from Lake Tanganyika to examine the relationship between sperm size and the presumed intensity of sperm competition. In contrast to previous reports of relatively short sperm in polygamous fishes across a variety of taxa, we found that polygamous cichlids had significantly longer sperm than their closest monogamous relatives. In addition, sperm length was significantly related to relative testis size (controlling for body size and phylogeny). The site of fertilization may also be correlated with sperm length, as species that fertilize in the female's buccal cavity had significantly shorter sperm than those that fertilized eggs on the substrate. Assuming that relatively large testes and polygamous mating are indicative of more intense sperm competition, these results indicate that sperm length is related to the intensity of sperm competition in this clade of cichlids, as has been found previously in insects, birds, and mammals. [ABSTRACT FROM AUTHOR]

Males of many bird species acquire a conspicuous breeding plumage through molt. Male rock ptarmigan (Lagopus mutus), however, become conspicuous in a unique way—as snow melts away from the tundra, their cryptic white winter plumage suddenly becomes exceptionally conspicuous, and remains so for at least 3 weeks. While males remain white, females molt into one of the most cryptic plumages known in birds. From our 17-year field study in arctic North America, we show that, unlike other birds, male rock ptarmigan eventually change from conspicuous to cryptic by soiling their plumage, thereby reducing their conspicuousness six fold before they molt to their cryptic summer plumage. Individual males began to soil their plumage as soon as their mates began egg-laying, and were maximally dirty and relatively cryptic by the time incubation began and their mates no longer fertilizable. Thus male plumage conspicuousness appears to serve a reproductive function. Moreover, both polygynous and bachelor males delayed soiling for a few days after monogamous males, as expected because of the prolonged mating opportunities available to them. We use these data to address a variety of hypotheses to explain both the conspicuousness of breeding males and their subsequent plumage soiling. Given the high predation rate recorded for male ptarmigan during the breeding season, we argue that male conspicuousness is best explained by sexual selection and that plumage soiling is an adaptation that reduces predation risk by increasing camouflage. [ABSTRACT FROM AUTHOR]

Female mate choice after copulation or spawning is cryptic when a female differentially influences the fertilization success of sperm from different males. We tested whether ovarian fluid could act as a potential mechanism of cryptic female choice (CFC) in chinook salmon (Oncorhynchus tshawytscha) by comparing how ovarian fluid from each of 7 females affected the sperm behavior of 11 different males. Using computer-assisted sperm analysis, we measured sperm velocity, motility, longevity, and linearity from the ejaculates of each male activated in the ovarian fluid from each female. Mean sperm swimming speed, path trajectory, and longevity differed significantly among males, and within males depended on the females ovarian fluid in which it was activated. Most important, the pattern of within-male variation in these traits also varied significantly among males in response to different females’ ovarian fluids. As sperm velocity is known to be a prime determinant of fertilization success in externally fertilizing fishes. This finding suggests that variation in the composition of female ovarian fluid may be a mechanism for CFC, whereby females differentially enhance the swimming speed of sperm from different males. Thus, female ovarian fluid can alter relative male fertilization success when there is intense sperm competition, as there is in this and other group spawning fish species. [ABSTRACT FROM AUTHOR]