Abstract
The period of parental care can be a demanding life-history stage because parents need to find sufficient resources to feed themselves and their offspring. Often, this is reflected by elevated baseline levels of glucocorticoids – hormones that regulate metabolism and energy allocation. During 10 breeding seasons, we studied plasma corticosterone (the major avian glucocorticoid) concentrations as a physiological correlate of parental expenditure in two closely related coucal species with fundamentally different mating systems: the sex-role reversed black coucal (Centropus grillii) with female competition and male-only care and the socially monogamous and biparental white-browed coucal (C. superciliosus). The two species live in the same habitat and share a similar breeding biology. However, female black coucals aggressively defend a territory and produce many eggs for their various male partners, and male black coucals feed their offspring much more frequently and rest less often than female and male white-browed coucals. These differences were reflected in baseline and stress-induced concentrations of corticosterone: male black coucals had higher baseline and stress-induced corticosterone concentrations when they were feeding young than outside a feeding context, and also the concentrations of female black coucals were higher during the main period of breeding when they defended territories and produced multiple clutches. In contrast, baseline and stress-induced concentrations of corticosterone in female and male white-browed coucals did not differ between periods when they were feeding young and periods without dependent offspring. Paradoxically, on an individual basis feeding effort was negatively related to baseline corticosterone in male black coucals and female white-browed coucals. In conclusion, corticosterone concentrations of coucals reflected differences in competition and parental roles and support the notion that a switch from biparental to uniparental care and an increase in mate competition may come at a physiological and energetic cost.
Highlights
The period of parental care is a demanding lifehistory stage
Parents need to find enough food to sustain themselves and their offspring. Such increasing demands are often reflected by increased levels of baseline glucocorticoids, steroid hormones that play a paramount role in energy metabolism and resource allocation (Harvey et al, 1984; Lea et al, 1992; Landys et al, 2006; Crespi et al, 2013)
Differences in baseline corticosterone may be species-specific, and a comparison among species may provide limited information regarding differences in allostatic states. With this limitation in mind, we looked at among-species differences in baseline corticosterone concentrations
Summary
The period of parental care is a demanding lifehistory stage During this time, parents need to find enough food to sustain themselves and their offspring. Parents need to find enough food to sustain themselves and their offspring Such increasing demands are often reflected by increased levels of baseline glucocorticoids, steroid hormones that play a paramount role in energy metabolism and resource allocation (Harvey et al, 1984; Lea et al, 1992; Landys et al, 2006; Crespi et al, 2013). Glucocorticoids mediate different levels of homeostasis that are required to tune critical internal variables to existing environmental conditions and life-history demands (Landys et al, 2006). Brood manipulation in tree swallows (Tachycineta bicolor) affected baseline corticosterone concentrations: females with enlarged broods showed a larger increase in baseline corticosterone between the incubation and the nestling phase than females with normal or reduced broods (Bonier et al, 2011, but see Kern et al, 2007, for a study on pied flycatchers where brood manipulation apparently had no effect on baseline corticosterone)
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