Corticosterone Concentrations Reflect Parental Expenditure in Contrasting Mating Systems of Two Coucal Species

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.

Sex roles, parental care and offspring growth in two contrasting coucal species

“…However, males may pay a physiological price for their higher feeding effort, because feeding male black coucals express higher levels of baseline and stress-induced corticosterone concentrations than non-feeding males. By contrast, feeding individuals of white-browed coucals do not show such elevations in baseline and stress-induced corticosterone [52]. Whether these physiological differences affect survival is unknown.…”

Male-only care and cuckoldry in black coucals: does parenting hamper sex life?

“…Our methods did not assign a systematic, clear role to the exact time point when male activities matter most, as a determinant of model performance; males only rarely changed state precisely between two alternative time points in the data, which-perhaps together with a stochastic delay between copulations (unobserved by us) and fertilization-explains our inability to distinguish precisely between timing alternatives. Time budget constraints may become more severe after a clutch has hatched, as the schedule of provisioning the young is not only physiologically and energetically demanding [49] but also leaves less time to rest, forage or mate [48]. Still, in our analyses, chances to sire young (as evidenced by paternity gains) do not drop to zero during this time either, which might indicate a role for active visits by females seeking fertilizations.…”

“…Hence, a male black coucal endures a 'time-out' period (sensu [43]) of about six weeks. Paternal care thus requires a significant time and energy investment [48,49], with the potential loss of mating opportunities. At first sight, this may appear to be a very special case applying only to polyandrous species with male-only care, but in fact, it applies to a broad range of mating systems in which males contribute to offspring care.…”

Enzymatic antioxidants but not baseline glucocorticoids mediate the reproduction–survival trade-off in a wild bird

“…While some studies show that absolute levels, as well as plastic changes, of baseline Cort are positively associated with the degree of parental care [26,27,36,71,72], other investigations disagree. For example, two recent correlative studies showed a negative association between chick feeding rates and baseline Cort concentrations [30,73]. Thus, the relationship between Cort and reproductive investment (or success) appears to vary across species and/or environmental context.…”

“…However, whether GCs play a role in mediating such trade-offs at low baseline concentrations is less clear, although their involvement has been hypothesized [22]. Baseline GCs are elevated when individuals experience increased energetic demands [11,12,17,18,[22][23][24][25], for example, in the reproductive season when parents provision their offspring [18,[26][27][28][29][30][31]. These findings prompted the hypothesis that baseline GCs may mediate trade-offs, but in an opposite way to stress-induced concentrations: baseline GCs would support investment in current reproduction at the expense of survival [22,32,33].…”