Maternal hormones as a tool to adjust offspring phenotype in avian species.
ABSTRACT Avian eggs contain substantial amounts of maternal hormones and so provide an excellent model to study hormone-mediated maternal effects. We review this new and rapidly evolving field, taking an ecological and evolutionary approach and focusing on effects and function of maternal androgens in offspring development. Manipulation of yolk levels of androgens within the physiological range indicates that maternal androgens affect behaviour, growth, morphology, immune function and survival of the offspring, in some cases even long after fledging. Descriptive and experimental studies show systematic variation in maternal androgen deposition both within and among clutches, as well as in relation to the sex of the embryo. We discuss the potential adaptive value of maternal androgen transfer at all these three levels. We conclude that maternal androgen deposition in avian eggs provides a flexible mechanism of non-genetic inheritance, by which the mother can favour some offspring over others, and adjust their developmental trajectories to prevailing environmental conditions, producing different phenotypes. However, the literature is less consistent than often assumed and at all three levels, the functional explanations need further experimental testing. The field would greatly benefit from an analysis of the underlying physiological mechanisms.
- SourceAvailable from: Marcel Eens[Show abstract] [Hide abstract]
ABSTRACT: It is well established that in many avian species, prenatal maternal resource allocation varies both between and within clutches and may affect offspring fitness. Differential allocation of maternal resources, in terms of egg weight and yolk composition, may therefore allow the female to adjust brood reduction and to fine-tune reproductive investment in accordance with the expected fitness returns. The adaptive value of such maternal resource allocation is thought to be context-dependent as well as species-specific. We investigated the effects of female preference for her mate on the allocation of prenatal maternal resources in the budgerigar, Melopsittacus undulatus, a monogamous species of parrot that shows an extreme hatching asynchrony. We assessed mate preferences in a two-way preference test and allowed females two breeding rounds: one with the preferred and one with the non-preferred partner. We found no effect of preference on either latency to lay or clutch size, but females mated with the preferred partner laid eggs that contained significantly more yolk. Their eggs also contained significantly more androstenedione but not testosterone. Our results suggest that in this species, female preference may influence maternal resource allocation, and that the functional roles of each androgen in the yolk should be considered separately. In addition, we found a significant effect of laying order on egg and yolk weight as well as on yolk testosterone and androstenedione levels. These measures, however, did not change linearly with the laying order and render it unlikely that female budgerigars compensate for the extreme hatching asynchrony by adjusting within-clutch allocation of prenatal maternal resources. Copyright © 2015. Published by Elsevier Inc.Hormones and Behavior 04/2015; 71. DOI:10.1016/j.yhbeh.2015.03.009 · 4.51 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Particularly in species with biparental care and low levels of extrapair paternity, sexual traits that honestly indicate phenotypic and genetic quality are expected. We investigated in the brown booby, Sula leucogaster, whether gular color displayed by males during courtship is related to direct or indirect benefits to females. We performed a cross-fostering experiment in order to identify the relative contribution of parental care and genetic effects on offspring condition. We found that rearing father gular color was positively related to parental care (offspring attendance and provisioning) and chick body mass increase, whereas the genetic father gular color was related to chick structural growth. Contrary to expectations, females paired to more colorful males laid smaller eggs and did not increase parental care. Interestingly, chicks from genetic mothers with more colorful gulars and chicks that hatched from larger eggs “begged” at higher rates to mothers than to fathers. Overall, the results suggest that male gular color may provide females with reliable information on mate genetic quality and parenting abilities.Behavioral Ecology 01/2015; 26(2). DOI:10.1093/beheco/aru204 · 3.16 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Maternal allocation shapes offspring phenotype by being tailored to parental phenotype and offspring sex. Because melanogenesis and immunity have partly common genetic control, maternal effects via egg immune factors and parental melanization may covary. Here, we tested whether barn swallows Hirundo rustica allocated antibodies against a novel antigen to their eggs according to embryo sex depending on maternal melanin-based coloration while controlling for paternal tail ornamentation. Egg antibody concentration increased with maternal plumage darkness in broods with relatively more females, whereas it decreased in broods with relatively more males. Thus, darker females allocated more antibodies to their eggs when offspring sex ratio was female biased, whereas paler females allocated more antibodies to the eggs when offspring sex ratio was male biased. These effects were independent of laying order. Our results are compatible with the hypotheses that maternal allocation to sons depends on their reproductive value as predicted by heritable melanin-based coloration and with the hypothesis of differential susceptibility of pheomelanic daughters to parasitism. These effects may depend on pleiotropy of the genes that control melanogenesis and immunity, which may differentially act on investment in self-maintenance and maternal effects. This study is the first study in vertebrates of the association between maternal effects on either sex via egg quality and parental melanization. The links between the genetic control of melanogenesis and of major fitness traits like immunity and the role of maternal effects in reproductive strategies prompt for more studies of the covariation between parental coloration and maternal sex-dependent allocation via egg quality.Behavioral Ecology 09/2014; 25(5):1248-1255. DOI:10.1093/beheco/aru112 · 3.16 Impact Factor