Don’t underestimate father: Effects of cryptic and non-cryptic paternal traits on maternal effect in a species without paternal care

Avian females can influence their offsprings’ phenotype by providing them certain with non-genetic materials, such as hormones, during early development. The attractiveness of their partners affect reproductive decisions such as how much of such non-genetic materials to provide. Partner attractiveness in many species is correlated with conspicuous external traits, such as comb size in Junglefowl, which are mediated by androgens such as testosterone. Circulating testosterone levels in large combed (attractive) male Junglefowl are higher than in small combed (unattractive) males, whereas ejaculate levels show a reversed pattern. This latter finding indicates that testosterone is a cryptic factor affecting females directly since females have steroid receptors in their reproductive tract. Indeed inseminating females with testosterone enriched ejaculates induces the production of larger eggs. However sons and daughters both from small combed and testosterone enriched male ejaculates showed a different growth pattern compared to offspring from large combed and control male ejaculates. This can be explained by differences in embryonic exposure to androgens, which enhances early growth, because females mated with attractive males exposed daughters in ovo to more androgens than sons, whereas the reversed pattern was observed when mated with unattractive males. Early exposure to testosterone has beneficial effects but may also be immunosuppressive, which has given rise to the hypothesis that only offspring from good quality fathers can endure early exposure. However, this hypothesis seems unlikely since there were no indications that either paternal quality or embryonic exposure to elevated testosterone levels affected offspring immunocompetence.