© Ruedi Aeschlimann
Carry-over effects from parental stress to the next generation
It is known that a pronounced stress situation during reproduction leads to brood abandonment. On the other hand, the effects of a short moderate stress situation on the breeding success and quality of the offspring are not well investigated. During egg laying bird mothers can influence the development of the embryos through hormone deposition into the eggs. In this project we investigate how maternal stress hormones influence the development of the offspring.
Recent studies showed that there are large individual differences in the effects of a stress situation on behaviour and fitness of birds. In the barn owls, the ability to cope with a stress situation is related to an individual's plumage coloration. The pronounced polymorphism in plumage coloration in the barn owl is genetically determined and only weakly influenced by environmental factors. The coloration of breast and belly varies in phaeomelanin-based coloration from whitish to reddish brown and in the number and size of eumelanin-based black spots. These genetically determined differences in coloration, which correlate with differences in behaviour and fitness, make the barn owl an ideal study species to investigate the consequences of elevated maternal stress hormones on the behaviour and fitness of the mother and its offspring.
a) Maternal effects: Do elevated glucocorticoids provide a mechanistic link between stress in mothers and offspring phenotype? Does this link depend on the genotype of the mother and the offspring?
b) Genetic-by-maternal effects: Are more eumelanic individuals better able to cope with a hormonal stress signal than less eumelanic individuals, and is this ability heritable?
The study was carried out on free living barn owls in the canton Vaud, Switzerland. To investigate the effects of a short period of stress during egg laying on the females' reproductive behaviour and on the fitness and phenotype of their offspring, we experimentally increased for a few hours per night the stress-hormone concentration of the mothers. To do so we fed the mothers with dead mice spiked with the stress hormone corticosterone. Each mother received, after having laid the first egg, one dead mouse per night for three consecutive nights. As a control, we had a group of breeding females fed with dead mice without corticosterone.
We assessed the quality of the females and their offspring by counting the number and size of black spots on breast and belly. To assess the effects of elevated stress hormones on the females, we reported the clutch size, breeding and rearing success of the females and the growth and reaction to a new stress situation in the offspring.
The barn owl is one of 50 priority species of the Swiss Species Recovery Programme. With the current project, we aim at closing the knowledge gaps on the effects of stress for a successful and sustained protection of breeding birds. The main aim is to gather knowledge about the subtle influences of stressors on the reproduction of birds. The acquired knowledge can also be used to help decision makers to protect wild birds during breeding.
Prof Alexandre Roulin, Université de Lausanne
Agricultural land use and human presence around breeding sites increase stress-hormone levels and decrease body mass in barn owl nestlings
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Kestrel and the Western Barn Owl
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