Abstract
IntroductionMaternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions. All of these pathways may, therefore, form significant sources of variation in maternal effects. Here, we focused on the maternal transfer of carotenoids and vitamin E to the egg yolk, using canaries as a model species. Maternal yolk carotenoids and vitamin E are known to generate significant phenotypic variation in offspring, representing examples of maternal effects. We studied the intra-individual consistency in deposition patterns across two years and the mother-daughter resemblance across two generations in order to estimate the level of heritable variation. The effects of the current environmental conditions were studied via a food supplementation experiment, while the consequences of past environmental conditions were estimated on the basis of the early growth trajectories.ResultsThere was a significant effect of the current environmental conditions on the yolk carotenoid and vitamin E deposition, but this effect varied between antioxidant components. The deposition of yolk carotenoids and vitamin E were linked to the process of yolk formation. Past environmental conditions did not contribute to the variation in yolk carotenoid and vitamin E levels nor did we find significant heritable variation.ConclusionsThe transfer of carotenoids or vitamin E may be an example where current environmental variation is largely passed from the mother to the offspring, despite the numerous intermediate physiological steps that are involved. Differences in the effect of the environmental conditions as experienced by the mother during laying may be due to differences in availability as well as physiological processes such as competitive exclusion or selective absorption.
Highlights
Maternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions
There was a significant effect of the current environmental conditions on the yolk carotenoid and vitamin E deposition, but this effect varied between antioxidant components
Past environmental conditions did not contribute to the variation in yolk carotenoid and vitamin E levels nor did we find significant heritable variation
Summary
Maternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions. Even though maternal effects have been well studied in birds, there is still little information available on heritable variation in maternal traits generating changes in offspring phenotype through variation in egg components One exception to this is the maternal transfer of hormones to the yolk, for which the heritability has recently been investigated, revealing a comparatively high degree of mother-daughter resemblance [13,14,15] (see [6] and references therein for the heritability of egg size). The degree of inheritance varied with the type of hormone investigated, with high heritability estimates being found for testosterone, but not for androstenedione deposition [13,14] (but see [15]) This suggests that the heritability of a given trait may depend on the physiological mechanisms of transfer that are available to the female. At present it is obviously most rewarding to study the heritability of the maternal deposition of egg components of which the transfer to the yolk is very different from the transfer of maternal androgens - such as in case of carotenoids or vitamin E
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