Maternal yolk testosterone does not modulate parasite susceptibility or immune function in great tit nestlings

Abstract

Summary 1.Maternal yolk hormones can enhance the development and phenotypic quality of nestling birds. Nevertheless, within species large differences in yolk androgen concentrations among clutches are observed. This differential allocation of maternal yolk hormones might be explained by a trade-off between beneficial effects of yolk androgens and their associated costs. 2. Potential costs include an increased susceptibility to parasites in nestlings exposed to high concentrations of yolk androgens during embryonic development, weaker immune response or increased levels of circulating corticosterone that indirectly reduce immune function. 3. In a field study, we manipulated yolk testosterone in great tit ( Parus major ) eggs and tested the nestling's susceptibility to ectoparasites as measured by the parasites' effect on growth, the cellular immune response, and the levels of circulating corticosterone. 4. At the end of the nestling period, nestlings originating from testosterone-injected eggs were heavier than control nestlings. This effect was strongest in nestlings at the end of the size hierarchy, as shown by a significant interaction between hormone treatment and the nestlings' size rank within nests. 5. High levels of yolk testosterone promoted growth of the nestling's body mass similarly in parasite-infested and parasite-free nests, and neither affected the levels of plasma corticosterone, nor the nestling's cell-mediated immune response. 6. In summary, our results do not show negative short-term effects of high concentrations of yolk testosterone on immune function or parasite susceptibility, but emphasize that maternal investment via deposition of yolk testosterone can promote fitnessrelated growth and development of nestlings.

Yolk androgens do not appear to mediate sexual conflict over parental investment in the collared flycatcher Ficedula albicollis

“…This method for manipulating yolk androgen levels has been successfully used and validated in previous studies (e.g. Tschirren et al, 2005). The hatching success of injected eggs did not differ between the control group (79.74%) and the androgen-manipulated group (79.77%, Wilcoxon test: p = 0.94, N = 66).…”

“…Indeed, elevated levels of androgens in the yolk can be costly for the chicks, as an immunosuppressive effect of androgens has been reported in some studies (e.g. Groothuis et al, 2005b;Müller et al, 2005;Navara et al, 2005; but see Andersson et al 2004;Tschirren et al, 2005;Müller et al, 2007b). Moreover, such elevated levels may require elevated circulating androgen levels in the female, which may, for example, delay or inhibit egg laying (e.g.…”

“…Groothuis et al, 2005a). In some bird species, androgens deposited in the egg yolk have been found to increase competitive ability of chicks (correlative data in Schwabl, 1993; experimental data in Eising et al, 2001), chick begging (experimental data : Schwabl, 1996;Schwabl and Lipar, 2002;Eising and Groothuis, 2003;Boncoraglio et al, 2006;von Engelhardt et al, 2006) and growth (experimental data: Schwabl, 1996;Eising et al, 2001;Pilz et al, 2004;Navara et al, 2005Navara et al, , 2006Tschirren et al, 2005). In other studies, however, no positive effect of elevated yolk androgens on begging or growth was found (experimental data: Sockman and Schwabl, 2000;Andersson et al, 2004;Pilz et al, 2004;Uller et al, 2005;Saino et al, 2006), or the effect depended on offspring sex (e.g.…”

Hormonally mediated maternal effects, individual strategy and global change

“…Maternal hormones can be major proximate factors affecting the propensity for dispersal. In different experimental manipulations of yolk testosterone in great tits, Tschirren and co-workers [190,191] proposed that the transfer of low concentrations of yolk androgens into the eggs might play an important role in modulating the offspring's dispersal behaviour. Birds hatched from eggs with experimentally elevated yolk testosterone concentrations dispersed over significantly longer distances.…”

Costly steroids: egg testosterone modulates nestling metabolic rate in the zebra finch

“…Groothuis et al 2005a;Gil et al 2006; but see Sockman & Schwabl 2000) as well as competitive ability of the chicks (e.g. Groothuis et al 2005a;von Engelhardt et al 2006), but they also negatively affect immune function of the offspring (Andersson et al 2004;Navara et al 2005;Groothuis et al 2005b;Mü ller et al 2005; but see Tschirren et al 2005;Navara et al 2006). However, since egg hormones increase growth and activity levels, they may not only entail costs in terms of immunosuppression, but also in terms of increased energy expenditure.…”