Mediators Of Maternal Effects Research Articles

Maternal Temperature, Corticosterone, and Body Condition as Mediators of Maternal Effects in Jacky Dragons (Amphibolurus muricatus).

AbstractTemperature is a crucial environmental component that imposes physiological constraints and ultimately produces variation in life-history traits. Temperatures experienced by mothers can influence offspring phenotypes, including growth and sex ratios, especially in ectothermic species. However, mechanisms by which thermal information can be passed onto offspring have been underexplored. Here, we investigated corticosterone as a potential mediator of thermal maternal effects. We held female jacky dragons (Amphibolurus muricatus) in two different thermal regimes (short [7 h] or long [11 h] basking treatments), then quantified plasma corticosterone levels and tested for correlations between the resulting corticosterone levels and reproductive outputs. Lizards in the long-bask treatment had significantly higher corticosterone levels than those in the short-bask treatment. Maternal corticosterone, in turn, had sex-dependent effects on offspring hatching size but was not associated with maternal reproductive effort or offspring sex or growth. In contrast, maternal body condition was strongly positively related to both reproductive output (including clutch size and total number of eggs) and offspring size at hatching but had no effect on offspring growth. Basking treatment also interacted with condition and corticosterone to affect egg mass and hatchling snout-vent length, respectively. When we tested for relationships between corticosterone levels and body condition, we found corticosterone to be negatively related to condition in long-bask lizards but only in the postbreeding season. These findings indicate that thermal opportunity alters physiology, with potential consequences for fitness. Moreover, the results suggest interactive influences of temperature, corticosterone, and condition as mediators of maternal effects.

Pre- and postnatal environmental effects as potential sources of variation in neophobic behaviour in canaries

Neophobia, the fear of new objects or stimuli, has been shown to be affected by both maternal effects and the environmental conditions experienced during development. However, both pathways have so far only been studied in isolation, even though maternal effects are known to have significant effects on early development. Thus, maternal yolk hormones — an important mediator of maternal effects — may affect neophobia both through direct effects on neophobic behaviour and/or by affecting the early development. Both pathways may even act in concert. We measured the neophobic response and habituation to novel food, as well as the response to a novel object in 8-months-old canaries (Serinus canaria). All birds hatched from eggs with elevated yolk testosterone levels or control-treated eggs, and grew up in distinct experimentally-manipulated positions within the sibling hierarchy, which allowed us to test whether and how the effects of prenatally elevated yolk testosterone levels on neophobic behaviour vary with the environmental conditions experienced post-hatch. Neither the experimentally-manipulated yolk testosterone levels nor the position within the sibling hierarchy had a direct effect on neophobic behaviour. The elevation of the yolk testosterone levels modulated the neophobic behaviour and the habituation to novel situations of juvenile canaries only in interplay with the experimentally manipulated position in the sibling hierarchy and offspring sex. The strongest increase of neophobic behaviour was observed in individuals that hatched from eggs with elevated yolk testosterone content while growing up in a superior position in the sibling hierarchy — and in males. However, these effects varied with the focal explanatory variable. Based on our results and a review of the literature, we conclude that neither prenatal maternal nor early environmental effects post-hatching form the main source of variation of neophobia in itself, but that the effects observed as well as the inconsistency thereof can best be explained by the interaction of different partly unknown pathways.