Are estrous mate preference shifts robust? This question is the subject of controversy within human evolutionary sciences. For nearly two decades, mate preference shifts across the ovulatory cycle were considered an important feature of human sexual selection, directing women's attention towards mates with indicators of "good genes" in their fertile phase, when conception is possible. However, several recent studies on masculine faces, bodies and behaviors did not find evidence supporting this account, known as the good genes ovulatory shift hypothesis. Furthermore, evidence that preferences for masculine characteristics in men's voices are related to women's cycle phase and hormonal status is still equivocal. Here, we report two independent within-subject studies from different labs with large sample sizes (N = 202 tested twice in Study 1; N = 157 tested four times in Study 2) investigating cycle shifts in women's preferences for masculine voices. In both studies, hormonal status was assessed directly using salivary assays of steroid hormones. We did not find evidence for effects of cycle phase, conception risk, or steroid hormone levels on women's preferences for masculine voices. Rather, our studies partially provide evidence for cycle shifts in women's general attraction to men's voices regardless of masculine characteristics. Women's relationship status and self-reported stress did not moderate these findings, and the hormonal pattern that influences these shifts remains somewhat unclear. We consider how future work can clarify the mechanisms underlying psychological changes across the ovulatory cycle.

Explaining intraspecific variation in reproductive tactics hinges on measuring associated costs and benefits. Yet, this is difficult if alternative (purportedly less optimal) tactics remain unobserved. We describe a rare alpha-position take-over by an immigrant male rhesus macaque in a population where males typically gain rank via succession. Unusually, male aggressiveness after the take-over correlated with rank and mating success. The new alpha achieved the highest mating and reproductive success. Nevertheless, he sired only 4 infants due to high extra-group paternity (59.3%). The costs of his immigration tactic were high: after the mating season ended, unable to deter coalitionary attacks by resident males, he was overthrown. The following year he had the highest relative annual weight loss and levels of immune activation among males in the group. Succession-based rank-acquisition in large, provisioned groups of macaques thus appears to be actively maintained by resident males, who impose high costs on challengers.

In non-human primate systems, the Ecological Model of Female Social Relationships (EMFSR) views variation in female social structure as adaptations to variation in recent past and/or current ecological conditions. Group size may be a major additional demographic factor affecting social structure through its effects on resource competition. In particular, in Resident Nepotistic Despotic (RND) societies, when resources are uniformly clumped, larger groups are expected to face higher levels of within-group contest competition (WGC) than smaller groups and to respond by showing more highly despotic social relationships than smaller groups. On the other hand, smaller groups are expected to face higher levels of between-group contest competition (BGC) and hence, show greater levels of intragroup tolerance (or lower despotism). While formal models do not explicitly predict this kind of variation within species, many researchers have investigated such intraspecific variation. Thus, we tested these predictions across three groups of free-ranging rhesus macaques (Macaca mulatta) of varying sizes on Cayo Santiago, Puerto Rico, where we were able to control for variation in resource-patch contestability and predation risk. Subjects were adult females. For each group, we collected data on (1) exposure and (2) behavioural reactions to WGC and BGC at two independent sets of clumped resources (feeding corrals and drinking stations) and (3) agonistic and affiliative social behaviour, using focal animal, all occurrences, and ad-libitum sampling methods. As predicted, our largest group showed the greatest levels of exposure and behavioural responses to WGC contexts. Likewise, our smallest group showed greatest levels of exposure and responses to BGC contexts. However, aspects of social structure did not vary across groups in directions predicted by the EMFSR. These findings are broadly consistent with several previous comparative tests of the model on other primate taxa that found strong links between group size, ecological factors and contest competitive regimes, but little or no evidence of links with social structure. Our study adds strength to these conclusions given our unique ability to control for several variables on Cayo Santiago. We suggest that our findings may be generalizable to several wild rhesus populations in North India, given that they have lived in similarly dense populations and have been frequently provisioned by humans for thousands of years.

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