title: An experimental analysis of the heritability of variation in glucocorticoid concentrations in a wild avian population.
abstract: Glucocorticoid hormones (CORT) are predicted to promote adaptation to variable environments, yet little is known about the potential for CORT secretion patterns to respond to selection in free-living populations. We assessed the heritable variation underlying differences in hormonal phenotypes using a cross-foster experimental design with nestling North American barn swallows (Hirundo rustica erythrogaster). Using a bivariate animal model, we partitioned variance in baseline and stress-induced CORT concentrations into their additive genetic and rearing environment components and estimated their genetic correlation. Both baseline and stress-induced CORT were heritable with heritability of 0.152 and 0.343, respectively. We found that the variation in baseline CORT was best explained by rearing environment, whereas the variation in stress-induced CORT was contributed to by a combination of genetic and environmental factors. Further, we did not detect a genetic correlation between these two hormonal traits. Although rearing environment appears to play an important role in the secretion of both types of CORT, our results suggest that stress-induced CORT levels are underlain by greater additive genetic variance compared with baseline CORT levels. Accordingly, we infer that the glucocorticoid response to stress has a greater potential for evolutionary change in response to selection compared with baseline glucocorticoid secretion patterns.
authors: Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Ramaley N122, UCB 334, Boulder, CO 80309, USA bjenkins@uwyo.edu.
authors: Brittany R
authors: BR
authors: Jenkins
authors: Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Ramaley N122, UCB 334, Boulder, CO 80309, USA.
authors: Maren N
authors: MN
authors: Vitousek
authors: Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Ramaley N122, UCB 334, Boulder, CO 80309, USA.
authors: Joanna K
authors: JK
authors: Hubbard
authors: Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Ramaley N122, UCB 334, Boulder, CO 80309, USA.
authors: Rebecca J
authors: RJ
authors: Safran
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D003345:Corticosterone / Q000097:blood / Q000235:genetics; D005260:Female; D005838:Genotype; D005938:Glucocorticoids / Q000097:blood* / Q000235:genetics; D008297:Male; D013312:Stress, Physiological / Q000502:physiology*; D046388:Swallows / Q000235:genetics* / Q000254:growth & development / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D003345:Corticosterone
keywords: animal model; barn swallow; cross-foster; environmental variation; glucocorticoids; heritability