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The pairing of female Rattus norvegicus with males copulated to satiety three weeks previously or recently copulated males shows that litters sired by rested males have higher sex ratios. The sex ratio bias exists only in litters conceived during a cycling estrus and is negatively associated with the time of mating completion. A relationship between sex ratio and rest-influenced mating behavior exists only in litters with fewer pups at birth than at implantation. The bias is probably due to adaptive litter decrease as post-implantation losses occur when uterine horns are crowded.

James argues that post-implantation loss may not be the reason for sex-ratio biases in rats. He argues, instead, that maternal hormone levels can influence whether ovum are likely to be fertilised by sperm carrying Y chromosomes. Such a mechanism prior to conception could occur but there may be other mechanisms affecting sex ratios following conception. There is a great deal of theory relating to sex ratio biases but less correlation and almost no explanation of mechanisms relating to such biases.

A study of sex-ratio biasing in Norway rats through targeted analysis revealed sex-ratio biasing to be opportunistic in response to physiological conditions and facultative in response to environmental ones. Sex-ratio biasing occurred at post-implantation and other reproductive stages. Post-implantation loss occurred when the number of offspring was less than the number of implantation sites.

Abstract: Purpose: Variation in sleep duration has been linked with mortality risk. The purpose of this review is to provide an updated evaluation of the literature on sleep duration and mortality, including a critical examination of sleep duration measurement and an examination of correlates of self-reported sleep duration. Methods: We conducted a systematic search of studies reporting associations between sleep duration and all-cause mortality and extracted the sleep duration measure and the measure(s) of association. Results: We identified 42 prospective studies of sleep duration and mortality drawing on 35 distinct study populations worldwide. Unlike previous reviews, we find that the published literature does not support a consistent finding of an association between self-reported sleep duration and mortality. Most studies have employed survey measures of sleep duration, which are not highly correlated with estimates based on physiologic measures. Conclusions: Despite a large body of literature, it is premature to conclude, as previous reviews have, that a robust, U-shaped association between sleep duration and mortality risk exists across populations. Careful attention must be paid to measurement, response bias, confounding, and reverse causation in the interpretation of associations between sleep duration and mortality. [Copyright &y& Elsevier]

Evidence suggests the putative human pheromone Δ4,16-androstadien-3-one (androstadienone), a natural component of human sweat, increases attention to emotional information when passively inhaled, even in minute amounts. However, the neural mechanisms underlying androstadienone’s impact on the perception of emotional stimuli have not been clarified. To characterize how the compound modifies neural circuitry while attending to emotional information, 22 subjects (11 women) underwent two fMRI scanning sessions, one with an androstadienone solution and one with a carrier control solution alone on their upper lip. During each session, participants viewed blocks of emotionally positive, negative, or neutral images. The BOLD response to emotional images (relative to neutral images) was greater during exposure to androstadienone in right orbitofrontal and lateral prefrontal cortex, particularly during positive image blocks. Androstadienone did not impact the response to social images, compared to nonsocial images, and results were not related to participant sex or olfactory sensitivity. To examine how androstadienone influences effective connectivity of this network, a dynamic causal model was employed with primary visual cortex (V1), amygdala, prefrontal cortex, and orbitofrontal cortex on each side. These models indicated that emotional images increased the drive from V1 to the amygdala during the control session. With androstadienone present, this drive to amygdala was decreased specifically for positive images, which drove downstream increases in orbitofrontal and prefrontal activity. This evidence suggests that androstadienone may act as a chemical signal to increase attention to positively valenced information via modifications to amygdala connectivity. [ABSTRACT FROM AUTHOR]

Abstract: We previously reported that paternally inherited human leukocyte antigen (HLA) alleles are a template for women''s preferences for male odors (p = 0.0007). However, it has been suggested that sequence variation in a nearby olfactory receptor (OR) cluster on chromosome 6p influences smell preference. To determine whether the HLA-linked OR genes contribute to previously observed HLA-mediated behaviors, we use the odor preference data from our earlier study in combination with a new resequencing study of four functional, HLA-linked OR genes in the same subjects. Our results indicate that OR alleles in the genes surveyed are not in linkage disequilibrium with HLA variation and do not explain the previous findings of HLA-associated odor preference. [Copyright &y& Elsevier]