Abstract
Avian egg yolks contain various amounts of maternally derived androgens that can modify offspring phenotype and adjust their development to the post-hatching environment. Seemingly adaptive variation in yolk androgen levels with respect to breeding density conditions or male attractiveness has been found in numerous studies. One important consideration that has been overlooked in previous research is the likely non-linear nature of hormone effects. To examine possible complex dose-response effects of maternal androgens on chick development, we experimentally administered three different androgen doses of the naturally occurring mixture of yolk testosterone and androstenedione to spotless starling eggs (Sturnus unicolor). We found that yolk androgens induce a non-linear dose-response pattern in several traits. Androgens had a stimulatory effect on hatchling body mass and nestling skeletal growth, but maximum values were found at intermediate doses, whereas our highest dose resulted in a decrease. However, the opposite U-shaped effect was found on nestling body mass. We also detected linear negative and positive effects on embryonic development period and nestling gape width, respectively. Our results suggest differential tissue responsiveness to yolk androgens, which may result in compromises in maternal allocation to produce adapted phenotypes. Because of the non-linear dose-response pattern, future investigations should carefully consider a wide range of concentrations, as the balance of costs and benefits may strongly differ depending on concentration.
Highlights
Females can influence the phenotype of their offspring through genes and somatic investments. Mousseau and Fox (1998) define maternal effects as epigenetic modifications of offspring phenotype caused by the environment provided by the mother during development
We studied the effects of our treatments on the length of the embryonic development period (EDP), hatching success, nestling survival and growth
Control eggs had a significantly lower hatching success than non-injected eggs from a random sample of nests in the same colony (χ2=8.64, d.f.=1, P=0.003), but hatching success was not influenced by treatment (χ2=1.58, d.f.=3, P=0.662), suggesting that the levels of testosterone+A4 that we used did not have a negative effect on embryo survival
Summary
Females can influence the phenotype of their offspring through genes and somatic investments. Mousseau and Fox (1998) define maternal effects as epigenetic modifications of offspring phenotype caused by the environment provided by the mother during development. Mousseau and Fox (1998) define maternal effects as epigenetic modifications of offspring phenotype caused by the environment provided by the mother during development. Testosterone, in turn, can be directly converted into E2 or DHT (Groothuis et al, 2005) The concentrations of these three androgens vary greatly both within and among species (Groothuis et al, 2005; Schwabl et al, 2007; Gil et al, 2007) and their effects on several offspring traits can be detected at different stages of offspring development (Mousseau and Fox, 1998; Griffith and Buchanan, 2010)
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