Robust manipulation of the behavior of Drosophila melanogaster by a fungal pathogen in the laboratory, bioRxiv, 2017-12-11
AbstractMany microbes induce striking behavioral changes in their animal hosts, but how they achieve this is poorly understood, especially at the molecular level. Mechanistic understanding has been largely constrained by the lack of a model system with advanced tools for molecular manipulation. We recently discovered a strain of the behavior-manipulating fungal pathogen Entomophthora muscae infecting wild Drosophila, and established methods to infect D. melanogaster in the lab. Lab-infected flies manifest the moribund behaviors characteristic of E. muscae infection hours before death, they climb upward, extend their proboscides and affix in place, then raise their wings, clearing a path for infectious spores to launch from their abdomens. We found that E. muscae invades the fly nervous system, suggesting a direct means by which the fungus could induce behavioral changes. Given the vast molecular toolkit available for D. melanogaster, we believe this new system will enable rapid progress in understanding the mechanistic basis of E. muscae’s behavioral manipulation in the fly.
biorxiv animal-behavior-and-cognition 200-500-users 2017Testing the parasite mass burden effect on host behaviour alteration in the Schistocephalus-stickleback system, bioRxiv, 2017-12-06
ABSTRACTMany parasites with complex life cycles modify their intermediate host’s behaviour, which has been proposed to increase transmission to their definitive host. This behavioural change could result from the parasite actively manipulating its host, but could also be explained by a mechanical effect, where the parasite’s physical presence affects host behaviour. We created an artificial internal parasite using silicone injections in the body cavity to test this mechanical effect hypothesis. We used the Schistocephalus solidus - threespine stickleback (Gasterosteus aculeatus) system, as this cestode can reach up to 92% of its fish host mass. Our results suggest that the mass burden brought by this macroparasite alone is not sufficient to cause behavioural changes in its host. Furthermore, our results show that wall-hugging (thigmotaxis), a measure of anxiety in vertebrates, is significantly reduced in Schistocephalus-infected sticklebacks, unveiling a new altered component of behaviour that may result from manipulation by this macroparasite.
biorxiv animal-behavior-and-cognition 0-100-users 2017Experimental evidence that female rhesus macaques (Macaca mulatta) perceive variation in male facial masculinity, bioRxiv, 2017-11-25
AbstractAmong many primate species, face shape is sexually dimorphic, and male facial masculinity has been proposed to influence female mate choice and male-male competition by signalling competitive ability. However, whether conspecifics pay attention to facial masculinity has only been assessed in humans. In a study of free-ranging rhesus macaques, Macaca mulatta, we used a two-alternative look-time experiment to test whether females perceive male facial masculinity. We presented 107 females with pairs of images of male faces – one with a more masculine shape and one more feminine – and recorded their looking behaviour. Females looked at the masculine face longer than at the feminine face in more trials than predicted by chance. Although there was no overall difference in average look-time between masculine and feminine faces across all trials, females looked significantly longer at masculine faces in a subset of trials for which the within-pair difference in masculinity was most pronounced. Additionally, the proportion of time subjects looked toward the masculine face increased as the within-pair difference in masculinity increased. This study provides evidence that female macaques perceive variation in male facial shape, a necessary condition for intersexual selection to operate on such a trait. It also highlights the potential impact of perceptual thresholds on look-time experiments.
biorxiv animal-behavior-and-cognition 0-100-users 2017General sexual desire, but not desire for uncommitted sexual relationships, tracks changes in women’s hormonal status, bioRxiv, 2017-06-27
AbstractSeveral recent longitudinal studies have investigated the hormonal correlates of both young adult women’s general sexual desire and, more specifically, their desire for uncommitted sexual relationships. Findings across these studies have been mixed, potentially because each study tested only small samples of women (Ns = 43, 33, and 14). Here we report results from a much larger (N = 375) longitudinal study of hormonal correlates of young adult women’s general sexual desire and their desire for uncommitted sexual relationships. Our analyses suggest that within-woman changes in general sexual desire are negatively related to progesterone, but are not related to testosterone or cortisol. We observed some positive relationships for estradiol, but these were generally only significant for solitary sexual desire. By contrast with our results for general sexual desire, analyses showed no evidence that changes in women’s desire for uncommitted sexual relationships are related to their hormonal status. Together, these results suggest that changes in hormonal status contribute to changes in women’s general sexual desire, but do not influence women’s desire for uncommitted sexual relationships.
biorxiv animal-behavior-and-cognition 100-200-users 2017No compelling evidence that preferences for facial masculinity track changes in women’s hormonal status, bioRxiv, 2017-05-13
AbstractAlthough widely cited as strong evidence that sexual selection has shaped human facial attractiveness judgments, evidence that preferences for masculine characteristics in men’s faces are related to women’s hormonal status is equivocal and controversial. Consequently, we conducted the largest ever longitudinal study of the hormonal correlates of women’s preferences for facial masculinity (N=584). Analyses showed no compelling evidence that preferences for facial masculinity were related to changes in women’s salivary steroid hormone levels. Furthermore, both within-subject and between-subject comparisons showed no evidence that oral contraceptive use decreased masculinity preferences. However, women generally preferred masculinized over feminized versions of men’s faces, particularly when assessing men’s attractiveness for short-term, rather than long-term, relationships. Our results do not support the hypothesized link between women’s preferences for facial masculinity and their hormonal status.
biorxiv animal-behavior-and-cognition 500+-users 2017A practical guide for inferring reliable dominance hierarchies and estimating their uncertainty, bioRxiv, 2017-02-24
AbstractMany animal social structures are organized hierarchically, with dominant individuals monopolizing resources. Dominance hierarchies have received great attention from behavioural and evolutionary ecologists. As a result, there are many methods for inferring hierarchies from social interactions. Yet, there are no clear guidelines about how many observed dominance interactions (i.e. sampling effort) are necessary for inferring reliable dominance hierarchies, nor are there any established tools for quantifying their uncertainty. In this study, we simulated interactions (winners and losers) in scenarios of varying steepness (the probability that a dominant defeats a subordinate based on their difference in rank). Using these data, we (1) quantify how the number of interactions recorded and hierarchy steepness affect the performance of three methods, (2) propose an amendment that improves the performance of a popular method, and (3) suggest two easy procedures to measure uncertainty in the inferred hierarchy. First, we found that the ratio of interactions to individuals required to infer reliable hierarchies is surprisingly low, but depends on the hierarchy steepness and method used. We then show that David’s score and our novel randomized Elo-rating are the two best methods, whereas the original Elo-rating and the recently described ADAGIO perform less well. Finally, we propose two simple methods to estimate uncertainty at the individual and group level. These uncertainty measures further allow to differentiate non-existent, very flat and highly uncertain hierarchies from intermediate, steep and certain hierarchies. Overall, we find that the methods for inferring dominance hierarchies are relatively robust, even when the ratio of observed interactions to individuals is as low as 10 to 20. However, we suggest that implementing simple procedures for estimating uncertainty will benefit researchers, and quantifying the shape of the dominance hierarchies will provide new insights into the study organisms.Highlights<jatslist list-type=bullet><jatslist-item>David’s score and the randomized Elo-rating perform best.<jatslist-item><jatslist-item>Method performance depends on hierarchy steepness and sampling effort.<jatslist-item><jatslist-item>Generally, inferring dominance hierarchies requires relatively few observations.<jatslist-item><jatslist-item>The R package “aniDom” allows easy estimation of hierarchy uncertainty.<jatslist-item><jatslist-item>Hierarchy uncertainty provides insights into the shape of the dominance hierarchy.<jatslist-item>
biorxiv animal-behavior-and-cognition 0-100-users 2017