Avian eggs contain substantial amounts of maternal yolk androgens, which have been shown to modulate offspring phenotype. The first studies on the functional consequences of maternal yolk androgens have focused on early life stages and their role in sibling competition. However, recent longitudinal studies reported long-lasting effects of maternal yolk androgens on offspring phenotype, mostly concerning traits that are sensitive to androgens. This suggests that maternal yolk androgens could play an important role in sexual selection, since the expression of many male sexual characters is testosterone-dependent. Using male canaries as a model, we examined the consequences of an experimental elevation of yolk testosterone concentrations on early development as well as long-lasting effects particularly on song, which is one of the most important sexual characters in male songbirds. Elevated yolk testosterone concentrations inhibited male growth, possibly in interaction with an existent ectoparasite exposure. Males hatched from testosterone-treated eggs (T-males) did not have enhanced competitive skills, in contrast to previous studies. The elevation of yolk testosterone concentrations delayed song development but did not affect adult song phenotype. This is intriguing, as yolk testosterone possibly induced developmental stress, which is known to reduce song quality. We hypothesize that yolk testosterone has either no direct effect on adult song phenotype, or that positive effects are merged by the negative effects of developmental stress. Finally, females mated with T-males invested more in their clutch indicating that females either assess T-males as more attractive (differential allocation hypothesis) or compensated for lower offspring viability (compensation hypothesis).
"Egg yolk testosterone concentrations reflect changes in environmental conditions experienced by females during egg formation (Sheldon, 2000; Gasparini et al., 2007; Safran et al., 2010; Remeš, 2011) and these alterations consequently manifest in the overall phenotype of the offspring. Maternal androgens are expected to have positive effects on fitness since they can modulate postnatal growth (Schwabl, 1996; Pilz et al., 2004; Müller et al., 2008; Vergauwen et al., 2011), behaviour (Schwabl, 1996; Eising et al., 2001; Niall Daisley et al., 2005; Bonisoli-Alquati et al., 2011; Müller et al., 2012) and secondary sexual characteristics (Eising et al., 2006; Bonisoli-Alquati et al., 2011) of the offspring. Negative influences on the immune system are often presented as a possible limitation of maternal androgen deposition. "
[Show abstract][Hide abstract] ABSTRACT: Yolk testosterone concentrations vary in response to environmental conditions and different testosterone contents can subsequently modify the phenotypic traits of offspring. Apart from effects on growth, proactive behaviour and secondary sexual characteristics, possible negative impacts of maternal testosterone on the immune system are often considered a limitation for its deposition. Effects of maternal testosterone can be modulated by postnatal environmental conditions, such as the availability of food resources. However, the majority of studies considering the effects of maternal testosterone on the immune system have been conducted under optimum conditions. In our study we evaluated the influence of genetic selection for high (HET) and low (LET) egg testosterone content in Japanese quail on immune responsiveness of offspring to phytohaemagglutinin (PHA) and lipopolysaccharide (LPS) stimulation under severe protein restriction. Protein restriction negatively influenced body weight and performance in the PHA-test. We observed an increase in Cort (corticosterone) and He/Ly (heterophil/lymphocyte ratio) after LPS, while no changes occurred in total IgY levels in the protein-restricted group. HET quails showed higher body mass and total IgY levels and lower He/Ly ratio than LET quails, while the PHA index and Cort concentration did not differ between lines. No interactions were found between protein restriction and genetic line. In conclusion, the immune response was not compromised under conditions of severe protein restriction in the faster growing HET line compared with the LET line. We hypothesise that the immune responsiveness of birds with higher yolk testosterone may be linked with other maternally-derived substances in a context-dependent manner.
Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology 11/2014; 177. DOI:10.1016/j.cbpa.2014.07.020 · 1.97 Impact Factor
"However, the only two experimental studies examining the effect of maternally derived testosterone on the development of their offspring song in canaries and starlings provided complex and nonsignificant results (Müller et al. 2008; Müller and Eens 2009). In the blood, circulating egg hormone concentrations, moreover, did not seem to pass to the egg yolk (Marshall et al. "
[Show abstract][Hide abstract] ABSTRACT: Maternal investment can play an important role for offspring fitness, especially in birds, as females have to provide their eggs with all the necessary nutrients for the development of the embryo. It is known that this type of maternal investment can be influenced by the quality of the male partner. In this study, we first verify that male song is important in the mate choice of female Eurasian reed warblers, as males mate faster when their singing is more complex. Furthermore, female egg investment varies in relation to male song characteristics. Interestingly, clutch size, egg weight, or size, which can be considered as an high-cost investment, is not influenced by male song characteristics, whereas comparably low-cost investment types like investment into diverse egg components are adjusted to male song characteristics. In line with this, our results suggest that female allocation rules depend on investment type as well as song characteristics. For example, egg white lysozyme is positively correlated with male song complexity. In contrast, a negative correlation exists between-song speed and syllable repetitiveness and egg yolk weight as well as egg yolk testosterone concentration. Thus, our results suggest that female egg investment is related to male song performance in several aspects, but female investment patterns regarding various egg compounds are not simply correlated.
Ecology and Evolution 04/2014; 4(8):1328-39. DOI:10.1002/ece3.1034 · 2.32 Impact Factor
"Indeed, long-term studies showed that egg androgens affected male morphological and secondary sexual traits (Strasser & Schwabl 2004; Eising et al. 2006; Rubolini et al. 2006; Riedstra et al. 2013), female reproduction (Rubolini et al. 2007), as well as socio-sexual behaviour (Strasser & Schwabl 2004; Eising et al. 2006; Partecke & Schwabl 2008; Bonisoli- Alquati et al. 2011a; Schweitzer et al. 2013) and personality traits (Tobler & Sandell 2007; Ruuskanen & Laaksonen 2010). These effects, however, were often inconsistent across studies and species (M€ uller et al. 2008; M€ uller & Eens 2009; Bonisoli-Alquati et al. 2011b; Ruuskanen et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Studies of avian species have shown that maternal effects mediated by the transfer of egg hormones can profoundly affect offspring phenotype and fitness. We previously demonstrated that the injection of a physiological amount of testosterone (T) in the eggs of ring-necked pheasants (Phasianus colchicus) disrupted the covariation among male morphological traits at sexual maturity and positively affected male mating success. Here, we investigate whether egg T exposure affected adult male circulating T levels at the onset of the breeding season (reflecting gonadal maturation), and the relationship between circulating T and male traits. Egg T exposure did not affect pre-mating plasma T. T levels were not associated with the expression of secondary sexual and non-sexual traits or socio-sexual behaviour (social rank, overall fighting ability and mating success). However, wattle brightness decreased with increasing circulating T in males hatched from T-eggs (T-males) but not among control males. In dyadic encounters during the peak mating period, control males with higher pre-mating T levels had higher chances of being dominant over other control males. However, higher pre-mating T levels did not predict success in male-male competition in encounters involving T-males. We suggest that the long-term effects of egg T on male phenotype do not originate from differential gonadal maturation according to egg T treatment. Rather, prenatal androgens may have priming effects on functioning of target tissues, translating into differential phenotypic effects according to androgen exposure during embryonic development.
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