Search

Heat waves are predicted to be detrimental for organismal physiology with costs for survival that could be reflected in markers of biological state such as telomeres. Changes in early life telomere dynamics driven by thermal stress are of particular interest during the early post‐natal stages of altricial birds because nestlings quickly shift from being ectothermic to endothermic after hatching. Telomeres of ectothermic and endothermic organisms respond differently to environmental temperature, but few investigations within species that transition from ectothermy to endothermy are available. Also, ambient temperature influences parental brooding behaviour, which will alter the temperature experienced by offspring and thereby, potentially, their telomeres. We exposed zebra finch nestlings to experimental heat waves and compared their telomere dynamics to that of a control group at 5, 12 and 80 days of age that encapsulate the transition from the ectothermic to the endothermic thermoregulatory stage; we also recorded parental brooding, offspring sex, mass, growth rates, brood size and hatch order. Nestling mass showed an inverse relationship with telomere length, and nestlings exposed to heat waves showed lower telomere attrition during their first 12 days of life (ectothermic stage) compared to controls. Additionally, parents of heated broods reduced the time they spent brooding offspring (at 5 days old) compared to controls. Our results indicate that the effect of heat waves on telomere dynamics likely varies depending on age and thermoregulatory stage of the offspring in combination with parental brooding behaviour during growth. [ABSTRACT FROM AUTHOR]

In birds, ambient temperature can influence adult incubation behaviour, energy budget, egg temperature and embryonic development, with downstream effects on offspring survival. Surprisingly, experimental manipulations of the whole nesting environment to test causes and consequences of variation in incubation pattern, energy balance, egg temperature and the duration of development are lacking to date. Here, we bred pairs of Zebra Finches Taeniopygia guttata under controlled conditions at 18 and 30 °C and measured clutch size, temperature, hatching success, parental attentiveness and the length of the embryonic period. We found that when breeding at the higher temperature, males, but not females, increased the number of incubation bouts on the nest. Instead, females, but not males, reduced their attentiveness towards the clutch overall. Eggs showed no temperature differences between the two treatments and bigger clutches experienced lower temperatures. This suggests that parental behaviour may buffer the effect of ambient conditions on the thermal profile of eggs, including species with high rates of parental attentiveness. Warmer conditions yielded higher hatching rates but did not cause measurable differences in the length of embryonic development. Still, smaller clutches hatched earlier in accordance with the higher temperature experienced. Additionally, we used data from the literature to calculate parental energy expenditure and demonstrate that this was substantially different across the two treatments, although predicted energy savings from reduced attentiveness at 30 °C appeared negligible. These results suggest that when food is available, ambient temperature and not energy trade‐offs may explain variation in incubation behaviour. [ABSTRACT FROM AUTHOR]

Variation in post-natal growth rates is substantial among organisms and especially strong among latitudes because tropical and south temperate species typically have slower growth than north temperate relatives. Metabolic rate is thought to be a critical mechanism underlying growth rates after accounting for allometric effects of body mass. However, comparative tests on a large spatial scale are lacking, and the importance of metabolism for growth rates remains unclear both within and particularly across latitudes., Songbirds exhibit strong interspecific variation in growth rates across geographic space, although within latitudes an association between metabolic rate and growth rate has not always been observed. Moreover, the hypothesis that differences in growth rates across latitudes reflect underlying differences in metabolism is untested. Here, we investigate these possibilities across north temperate, south temperate and tropical study sites., Phylogenetic analyses showed that, for a given body mass, metabolic rates of north temperate nestlings were higher than tropical and south temperate species. Metabolic rates controlled for body mass correlated with post-natal growth rates both within and among latitudes. Offspring body mass explained substantial residual variation in growth rates as expected under classic allometric theory., Our results suggest that variation in metabolic rates has an important influence on broad patterns of avian growth rates at a global scale. We suggest further studies that address the ecological and physiological costs and consequences of variation in metabolism and growth rates. [ABSTRACT FROM AUTHOR]

Developmental stress affects a range of phenotypic traits in later life-history stages. These long-term effects are thought to provide information to potential mates on individual quality and the ability to cope with adversity (i.e. the developmental stress hypothesis). Developmental stress appears to affect learning broadly, but the direction of effect is not always consistent between studies. This disparity may arise from indirect effects of developmental stress on other physiological or behavioural systems, which can affect outcomes in learning paradigms. Here, we examine the effect of elevated corticosterone (the dominant avian stress hormone) during development on the ability of zebra finches, Taeniopygia guttata, to learn a novel foraging task as adults. Additionally, we evaluate treatment effects on metabolism, to determine whether changes in metabolic rate indirectly alter learning results. We found that birds exposed to elevated corticosterone during development solved a foraging task faster than control siblings. This outcome could result from differences, not in learning ability, but in motivation for reward. However, we found no difference between treatment groups in metabolic rate. Hence, our results indicate that developmental stress can increase learning ability, and suggest that the effects of stress will vary based on the type of learning studied. [ABSTRACT FROM AUTHOR]