Maximum gonad investment reveals male bias when temperature decreases or latitude increases for a broadcast-spawning intertidal chiton (Polyplacophora: Chitonida)

Appraising sexual asymmetry during maximum gonad investment (MGI) offers a sharp tool to evaluate the reproductive response of species to climate by coupling extrinsic and intrinsic factors. We comparatively analyze how the mass and physiological male and female gonad investments of the broadcast-spawning intertidal Chiton articulatus in two populations from the Mexican Tropical Pacific respond to the thermal phases of cold “La Niña” and warm “El Niño.” We found that local rather than regional temperature modulates MGI intensity and breadth in this species, evidencing higher MGI levels in the southern tropical zone (Oaxaca). Male gonad investment was higher than that of females during neutral and cold phases compared to warm thermal phases. Physiological gonad investment during MGI suggests that males spawn before females, and the adult sex ratio of each population was close to unity. Our results suggest reproductive success regulation through sexual asymmetry in both mass and physiological gonad investment, modulated by temperature changes due to thermal phases. The male bias in gonad investment found under neutral to cold temperatures suggests physiological resilience in this species, especially considering its habitat and the impact of climate change· The MGI value is a phenotypic trait that varies as a function of temperature.