Sexual versus individual differentiation: the controversial role of avian maternal hormones.
ABSTRACT Avian embryos are exposed not only to endogenous sex steroids, which are produced by their gonads and have a key role in sexual differentiation, but also to maternal steroids transferred into the egg yolk, which can modulate the development of individual differences in behavior. Studies of maternal hormones have primarily focused on ultimate questions (evolutionary trade-offs, functional significance), whereas proximate mechanistic questions have been largely ignored. A central problem that must be addressed is how exposure to maternal hormones affects the individual phenotype without interfering with sexual differentiation. Separate effects could result from the action of different hormones, at different doses or at different times, on different targets.
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: Maternal effects can result in transgenerational phenotypic plasticity, in which environmental variation experienced by mothers is translated into phenotypic variation in offspring. Although maternal effects have been a focus of much recent research, little is known about the long-term consequences of disturbance of the maternal social environment on offspring phenotype in socially monogamous and biparental species. We hypothesized that pair separation followed by re-pairing may generate maternal effects on offspring development. Here, we gave previously paired female zebra finches access to new males 6 days following removal of their original partner to assess experimentally the effects of re-pairing (an ecologically relevant form of social disturbance) on female reproductive investment, yolk corticosterone concentrations and subsequent offspring phenotype. Pair disruption boosted growth in female offspring and delayed the development of plumage colour sex dimorphism in males. Although yolk corticosterone concentrations were not affected by the treatment, offspring from treated mothers were less responsive to social isolation in a novel environment compared to control offspring. This is, to our knowledge, the first study demonstrating that maternal re-pairing prior to hatching has long-lasting effects on offspring phenotype in a socially monogamous and biparental species. Our results also suggest that prehatching maternal effects of this social disturbance are not mediated by maternal yolk corticosterone. Additional studies are required to determine the potential pathways of these maternal effects (e.g. other hormones, epigenetic programming, protein/nutrient content of eggs, etc.) and their adaptive value.Animal Behaviour 04/2014; 90:195–204. DOI:10.1016/j.anbehav.2014.01.022 · 3.07 Impact Factor