Abstract
Maternal hormones are important mediators of prenatal maternal effects in animals. Although their effects on offspring phenotype are often sex-specific, the reason why sometimes sons are more sensitive to prenatal hormone exposure and sometimes daughters is not well understood. Here I combine an experimental manipulation of yolk testosterone concentration in the egg and quantification of selection acting on yolk androgen-sensitive traits in a natural population of great tits (Parus major) with a literature review to test the hypothesis that sex-specific selection on traits affected by yolk androgens determines which sex is more sensitive to prenatal hormone exposure. An experimental increase of the testosterone content in the egg boosted the post-hatching growth of male, but not female great tit nestlings. However, I found no evidence that survival selection on body mass or size is acting differently in the two sexes. A literature review revealed that yolk androgen manipulations affect the growth of males and females differently across species. Interestingly, in studies performed in the wild a significant association between the strength and direction of sexual size dimorphism and sex-specific sensitivities to yolk androgens was observed. In studies performed in captivity, no such relationship was found. Thus, across species there is some evidence that sex-specific selection on body size influences how strongly growth trajectories of males and females are affected by maternally-derived yolk androgens.
Highlights
Environmental conditions encountered early in life can modify developmental processes and can have long-term effects on the morphology, physiology and behavior of organisms [1]
I tested if natural selection acts in a sex-specific way on fledging mass and size, which are differentially affected by yolk androgens in male and female great tit nestlings
There was no evidence that survival selection is acting in a sex-specific way on two traits that were differentially affected by yolk androgens in male and female great tits
Summary
Environmental conditions encountered early in life can modify developmental processes and can have long-term effects on the morphology, physiology and behavior of organisms [1]. Mothers can considerably influence the environment encountered by the offspring during early development by differentially transferring resources and cues to the developing young [1]. Important mediators of such prenatal maternal effects are hormones that are transferred by the mother during pregnancy [2,3] or egg laying [4]. Experimental studies have demonstrated that maternal hormones, and in particular maternal androgens, can affect various aspects of offspring phenotype, including growth, physiology and behavior (reviewed in [5,6]).
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