Genes Integral to the Reproductive Function of Male Reproductive Tissues Drive Heterogeneity in Evolutionary Rates in Japanese Quail

Genetic parameters for cloacal gland, sexual maturity, reproductive organs weight, and body weight in meat-type quail

Selection to increase body weight in poultry can hamper reproduction traits and compromise production efficiency. Thus, attention to reproduction traits is essential to improving the sustainability of breeding programs. Data from a domestic quail breeding program for meat production were used to estimate genetic parameters. We analyzed five traits: 4-week body weight, age at sexual maturity for males and females, cloacal gland area, female, and male reproductive organs weights. A multi-trait mixed model analysis with fixed effects of generation/hatch was performed, assuming environmental covariance equals zero for sex-limited traits. Heritability estimates range from low to moderate for male sexual maturity and cloacal gland area, and high for other traits. Intersexual genetic correlation for age at sexual maturity is positive, which can lead to correlated responses in the other sex. Reproductive organs weights are genetically correlated with body weight, but not significantly between sexes and nor with sexual maturity. Genetic correlations for the cloacal gland area were positive with body weight and negative with age at sexual maturity of males and females, demonstrating a potential use of this trait for selection with favorable outcomes in reproduction. The use of the cloacal gland area can be used in the same way as the scrotal circumference in mammals, improving female reproduction traits by selecting a trait recorded in males.

Developing a transcriptomic framework for testing testosterone-mediated handicap hypotheses

Sexually selected traits are hypothesized to be honest signals of individual quality due to the costs associated with their maintenance, development, and/or production. Testosterone, a sex steroid associated with the development and/or production of sexually selected traits, has been proposed to enforce the honesty of sexually selected traits via its immunosuppressive effects (i.e., the Immunocompetence Handicap Hypothesis) and/or by influencing an individual's exposure/susceptibility to oxidative stress (i.e., the Oxidation Handicap Hypothesis). Previous work testing these hypotheses has primarily focused on physiological measurements of immunity or oxidative stress, but little is known about the molecular pathways by which testosterone could influence immunity and/or oxidative stress pathways. To further understand the transcriptomic consequences of experimentally elevated testosterone in the context of handicap hypotheses, we used previously published RNA-seq data from studies that measured the transcriptome of individuals treated with either a testosterone-filled or an empty (i.e., control) implant. Two studies encompassing three species of bird and three tissue types fit our selection criteria and we reanalyzed the data using weighted gene co-expression network analysis. Testosterone-treated individuals exhibited signatures of immunosuppression and our results describe the molecular pathways underlying this effect. We also provide some evidence to suggest that the transcriptomic signature of immunosuppression is evolutionarily conserved between the three species. While our results provide no evidence to suggest testosterone mediates handicaps via pathways associated with oxidative stress, they do support the hypothesis that testosterone enforces the honesty of sexually-selected traits by influencing an individual's immunocompetence. Overall, this study develops a framework for testing testosterone-mediated handicap hypotheses and provides guidelines for future integrative and comparative studies focused on the proximate mechanisms mediating sexually selected traits.