Yolk testosterone, postnatal growth and song in male canaries.
ABSTRACT 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).
SourceAvailable from: Zuzana Kankova[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; DOI:10.1016/j.cbpa.2014.07.020 · 2.37 Impact Factor
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ABSTRACT: Hormones of maternal origin transferred to the eggs of oviparous species have been shown to significantly affect offspring development. Furthermore, there is now increasing evidence that these effects may last into adulthood. This underlines the persistence of yolk hormone-mediated maternal effects as well as their trans-generational potential as these changes may involve fitness-related traits such as mate choice behaviour, reproductive traits and longevity. Here, we tested the potential of yolk testosterone to affect sexual selection by experimentally increasing the yolk testosterone levels via egg injections. We focused on two central axes of sexual selection, male–male competition for access to a female (intra-sexual selection) and female mate choice behaviour (inter-sexual selection), using canaries (Serinus canaria) as a model species. Neither male agonistic behaviour nor access to the opposite sex, as measured in staged male–male encounters in the presence of a female, were affected by experimentally elevating yolk testosterone levels. We did not find any evidence for effects on female mate choice behaviour either, given the lack of significant effects on mate choice activity, consistency in female mate choice or choosiness. In conclusion, our results indicate that the consequences of yolk testosterone for sexual selection through changes in behavioural traits, which are expressed during pair formation or male–male competition, are probably limited.Behavioral Ecology and Sociobiology 08/2014; 68(8). DOI:10.1007/s00265-014-1740-9 · 3.05 Impact Factor