Sexual signals reveal males’ oxidative stress defences: Testing this hypothesis in an invertebrate

Abstract The hypothesis that sexual traits reveal the oxidative stress resistance of their bearers has been widely tested in vertebrates but remains unexplored in invertebrates. Here, Hetaerina americana was used to test whether oxidative stress defences are advertised by male wing spot size and colour (a male sexual trait). To this end, we investigated (1) whether oxidative stress reduced survival, (2) whether wing spot size revealed males’ antioxidant defences and (3) how wing spot size and colour were affected by oxidative stress. We elevated oxidative stress by injecting adult males with paraquat (PQ, a compound that favours the production of free radicals) and then examined how this affected male survival and wing spot size. We then related the expression of wing spot size to indicators of oxidative stress—hydrogen peroxide (H 2 O 2 ) and total antioxidant capacity (TAC), super oxide dismutase (SOD) and catalase (CAT)—in adult males (whose wing spot is fixed) injected with PQ . In teneral males, whose wing spots are still forming, we compared wing spot size, colour (red and yellow chroma) and brightness in individuals injected with PQ or water as a control. Oxidative stress reduced the survival of adult and teneral males. While the H 2 O 2 and TAC markers of antioxidant defences were positively correlated with wing spot size, there was no correlation with CAT and a negative correlation with SOD . In teneral males, PQ increased the yellow chroma and brightness of wing spots, but did not affect spot size or red chroma. Our results highlight the importance of measuring different markers as indicators of male oxidative stress defences, and that the sexual signals of invertebrates may reveal the oxidative stress status of their bearers. A plain language summary is available for this article.