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

Abstract

The decision to provide parental care is often associated with trade-offs, because resources allocated to parental care typically cannot be invested in self-maintenance or mating. In most animals, females provide more parental care than males, but the reason for this pattern is still debated in evolutionary ecology. To better understand sex differences in parental care and its consequences, we need to study closely related species where the sexes differ in offspring care. We investigated parental care in relation to offspring growth in two closely related coucal species that fundamentally differ in sex roles and parental care, but live in the same food-rich habitat with a benign climate and have a similar breeding phenology. Incubation patterns differed and uniparental male black coucals fed their offspring two times more often than female and male white-browed coucals combined. Also, white-browed coucals had more ‘off-times’ than male black coucals, during which they perched and preened. However, these differences in parental care were not reflected in offspring growth, probably because white-browed coucals fed their nestlings a larger proportion of frogs than insects. A food-rich habitat with a benign climate may be a necessary, but—perhaps unsurprisingly—is not a sufficient factor for the evolution of uniparental care. In combination with previous results (Goymann et al. 2015 J. Evol. Biol. 28, 1335–1353 (doi:10.1111/jeb.1265710.1111/jeb.12657)), these data suggest that white-browed coucals may cooperate in parental care, because they lack opportunities to become polygamous rather than because both parents were needed to successfully raise all offspring. Our case study supports recent theory suggesting that permissive environmental conditions in combination with a particular life history may induce sexual selection in females. A positive feedback loop among sexual selection, body size and adult sex-ratio may then stabilize reversed sex roles in competition and parental care.

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

“…However, when feeding dependent offspring, individual male black coucals have a four-fold higher feeding rate than individual white-browed coucals and, in between feeding bouts, rest only 1/3rd of the time white-browed coucals do (Goymann et al, 2016). These data suggest a substantial difference in time and energy costs of offspring care between male black coucals and pairs of whitebrowed coucals.…”

“…Further details regarding the study site can be found in the work by Goymann et al (2015Goymann et al ( , 2016.…”

“…Black coucals are migrants and hence start breeding slightly later than white-browed coucals, which stay in the area year-round (Goymann et al, 2015). Further comparative details on the life-history, breeding biology, and parental behavior of the two species can be found in the studies by Goymann et al (2015Goymann et al ( , 2016.…”

“…In contrast to the black coucal, the whitebrowed coucal is the least sexually dimorphic of all 26 coucal species with females being only ca. 13% larger than males, and the one with the greatest similarity in sex roles (Van Someren, 1956;Rowan, 1983;Andersson, 1995;Goymann et al, 2015Goymann et al, , 2016. Both partners sing and often duet (Brumm and Goymann, 2017), jointly defend a territory, and form socially monogamous pairs with both partners contributing to offspring care equally (Goymann et al, 2016).…”

On the natural history of duetting in White-browed Coucals: sex- and body-size-dependent differences in a collective vocal display

“…This species is a nesting Old World Cuckoo, occurring in sub-Saharan Africa (Fry et al 1988). The breeding system and life history of White-browed Coucals have only recently been studied (Goymann et al 2015(Goymann et al , 2016. They are year-round resident birds that live in socially monogamous pairs, and both partners contribute to parental care.…”