Abstract
Testosterone (T) mediates a variety of traits that function in competition for mates, including territorial aggression, ornaments, armaments, and gametogenesis. The link between T and mating competition has been studied mainly in males, but females also face selection pressures to compete for mates. Sex-role reversed species, in which females are the more competitive sex, provide a unique perspective on the role of T in promoting competitive traits. Here, we examine patterns of T secretion in sex-role reversed Northern Jacanas (Jacana spinosa) during breeding, when females are fertile and males are either seeking copulations or conducting parental care. We measured baseline levels of T in circulation along with a suite of behavioral and morphological traits putatively involved in mating competition. We evaluated hypotheses that levels of T track gonadal sex and parental role, and we begin to investigate whether T and competitive traits co-vary in a sex- and stage-specific manner. Although females had higher expression of competitive traits than males at either breeding stage, we found that females and incubating males had similar levels of T secretion, which were lower than those observed in copulating males. T was correlated with wing spur length in females and testes mass in copulating males, but was otherwise uncorrelated with other competitive traits. These findings suggest that levels of T in circulation alone do not predict variation in competitive traits across levels of analysis, including gonadal sex and parental role. Instead, our findings coupled with prior research indicate that selection for female mating competition and male care may generate different physiological regulation of competitive traits in jacanas.
Highlights
In role reversed species, females face stronger competition and males care for offspring
We examine testosterone (T) and competitive traits in female and male jacanas
Circulating T is similar in females and incubating males, but higher in copulating males
Both gonadal sex and parental role shape patterns of T secretion
Physiological regulation of competitive traits may differ in female and male jacanas
Footnotes
We have provided more information on sample collection. We have also made more caveats regarding small sample sizes. We have re-analyzed our phenotypic co-variation results between testosterone and competitive traits to control for multiple testing. We have also added an additional table comparing our findings to that of other sex-role reversed species.