Social monogamy vs. polyandry: ecological factors associated with sex roles in two closely related birds within the same habitat

Why mainly males compete and females take a larger share in parental care remains an exciting question in evolutionary biology. Role‐reversed species are of particular interest, because such ‘exceptions’ help to test the rule. Using mating systems theory as a framework, we compared the reproductive...

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Bibliographic Details
Published in:	Journal of evolutionary biology Vol. 28; no. 7; pp. 1335 - 1353
Main Authors:	Goymann, W, Makomba, M, Urasa, F, Schwabl, I
Format:	Journal Article
Language:	English
Published:	Switzerland Birkhäuser 01-07-2015 Blackwell Publishing Ltd
Subjects:	adults Animal Migration Animal reproduction Animals Birds Body Weight breeding Clutch Size coucal Ecosystem Evolutionary biology Female females Habitats Male males mating system mating systems migration migratory behavior monogamy Nesting Behavior nests parental care polyandry Population Density predation Predatory Behavior Sex Characteristics Sex Ratio Sexual Behavior, Animal sexual dimorphism sexual selection sex‐role reversal System theory Tanzania variance variance in reproductive success Tanzania variance in reproductive success parental care sex-role reversal mating system coucal sexual selection migration predation sex ratio
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Summary:	Why mainly males compete and females take a larger share in parental care remains an exciting question in evolutionary biology. Role‐reversed species are of particular interest, because such ‘exceptions’ help to test the rule. Using mating systems theory as a framework, we compared the reproductive ecology of the two most contrasting coucals with regard to sexual dimorphism and parental care: the black coucal with male‐only care and the biparental white‐browed coucal. Both species occur in the same lush habitat and face similar ecological conditions, but drastically differ in mating system and sexual dimorphism. Black coucals were migratory and occurred at high breeding densities. With females being obligatory polyandrous and almost twice as heavy as males, black coucals belong to the most extreme vertebrates with reversed sexual dimorphism. Higher variance in reproductive success in fiercely competing females suggests that sexual selection is stronger in females than in males. In contrast, resident white‐browed coucals bred at low densities and invariably in pairs. They were almost monomorphic and the variance in reproductive success was similar between the sexes. Black coucals were more likely to lose nests than white‐browed coucals, probably facilitating female emancipation of parental care in black coucals. We propose that a combination of high food abundance, high population density, high degree of nest loss and male bias in the adult sex ratio represent ecological conditions that facilitate role reversal and polyandry in coucals and terrestrial vertebrates in general.
Bibliography:	http://dx.doi.org/10.1111/jeb.12657 Data deposited at Dryad:doi 10.5061/dryad.4nt54 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1010-061X 1420-9101
DOI:	10.1111/jeb.12657