In addition to direct mortality, predators can have indirect effects on prey populations by affecting prey behaviour or physiology. For example, predator presence can increase stress hormone levels, which can have physiological costs. Stress exposure accelerates the shortening of telomeres (i.e. the protective caps of chromosomes) and shorter telomeres have been linked to increased mortality risk. However, the effect of perceived predation risk on telomeres is not known. We investigated the effects of continuous predator threat (nesting Eurasian pygmy owl Glaucidium passerinum) on telomere dynamics of both adult and partially cross-fostered nestling pied flycatchers (Ficedula hypoleuca) in the wild. Females nesting at owl-inhabited sites showed impaired telomere maintenance between incubation and chick rearing compared to controls, and both males and females ended up with shorter telomeres at owl-inhabited sites in the end of chick rearing. On the contrary, both original and cross-fostered chicks reared in owl sites had consistently longer telomeres during growth than chicks reared at control sites. Thus, predation risk may cause a long-term cost in terms of telomeres for parents but not for their offspring. Predators may therefore affect telomere dynamics of their preys, which could have implications for their ageing rate and consequently for population dynamics.Electronic supplementary materialThe online version of this article (10.1007/s00442-019-04529-3) contains supplementary material, which is available to authorized users.
Environmental shifts may induce sudden reversals in the relative quality or sexual attractiveness of mates (ecological crossovers) leading to non-directional sexual selection. Studies on such ecological crossovers induced by environmental shifts during the nonbreeding season are particularly rare. We studied the interactive effects between nonbreeding conditions and a male white wing patch on the breeding success of breeding pairs and the local survival of females in a migratory passerine population over a 32-year period. After dry winters, females paired with large-patched males were more likely to survive than those paired with small-patched males, and vice versa after moist winters. Moreover, after dry winters, large-patched males succeeded in attracting females that laid large clutches, while small-patched males bred with females that laid small clutches, and vice versa after moist winters. This phenomenon led to a difference in fledgling numbers only during years with dry winters and high precipitation during the breeding season. The selection on this male trait and its signaling value to females thus depended on a complex interaction between conditions both at the nonbreeding and breeding grounds. We show that it is important to consider conditions during the nonbreeding season when examining the effects of sexual ornaments on fitness.
Early-life conditions are crucial determinants of phenotype and fitness. The effects of pre- and postnatal conditions on fitness prospects have been widely studied but their interactive effects have received less attention. In birds, asynchronous hatching creates challenging developmental conditions for the last-hatched chicks, but differential allocation in last-laid eggs might help to compensate this initial handicap. The relative importance and potential interaction between pre- and post-hatching developmental conditions for different fitness components remains mostly unknown. We manipulated hatching order in wild pied flycatchers (Ficedula hypoleuca), creating three groups: Natural asynchrony (last-laid eggs hatching last), Reversed asynchrony (last-laid eggs hatching first) and Hatching synchrony (all eggs hatching at once). We examined the effects of these manipulations on early-life survival, growth and telomere length, a potential cellular biomarker of fitness prospects. Mortality was mostly affected by hatching order, with last-hatched chicks being more likely to die. Early-life telomere dynamics and growth were influenced by the interplays between laying and hatching order. Last-laid but first-hatched chicks were heavier but had shorter telomeres 5 days after hatching than their siblings, indicating rapid early growth with potential adverse consequences on telomere length. Synchronous chicks did not suffer any apparent cost of hatching synchronously. Impaired phenotypes only occurred when reversing the natural hatching order (i.e. developmental mismatch), suggesting that maternal investment in last-laid eggs might indeed counterbalance the initial handicap of last-hatched chicks. Our experimental study thus highlights that potential interplays between pre- and post-natal environments are likely to shape fitness prospects in the wild.
Striking variation in melanin coloration within natural populations is likely due to the different fitness outcomes of alternative phenotypes in varying environmental conditions. There are two types of melanin: eumelanins yield blackish hues, whereas pheomelanins yield reddish hues. The production of eumelanins requires low levels of glutathione (GSH), which is the most important intracellular antioxidant, whereas the production of pheomelanins requires high levels of GSH. We investigated the oxidative status of male pied flycatchers (Ficedula hypoleuca) with different degrees of melanin coloration under different temperatures during the nestling period. Moreover, we assessed the oxidative status of offspring in relation to their biological or foster father's melanin coloration and ambient temperature. To separate offspring genotype effects and paternal effects in different temperatures, we used a partial cross-foster design. The temperature differently affected the oxidative status of differently colored male pied flycatchers and their foster offspring. When the weather was relatively cold, black males had higher glutathione S-transferase levels compared with brown males, indicating enhanced stress in black males. Foster offspring of black males had a lower ratio between reduced and oxidized GSH followed by higher total amount of GSH than foster offspring of brown males. Thus, foster offspring of black males seem to suffer from oxidative stress under relatively cold weather compared with those of brown males, and vice versa under relatively warm weather. Although differently colored males experienced changes in their oxidative status under different temperatures, the link between paternal melanin coloration and offspring oxidative stress appears to be environmentally induced.
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