Reproductive traits in the southernmost landlocked population of the fish Galaxias maculatus

Abstract

This work aimed to study the reproductive traits of the southernmost landlocked population of Galaxias maculatus living under extreme environmental conditions (54.5° S). Individuals were measured, weighed, sexed, and dissected. The reproductive cycle was analyzed based on the monthly variation of the gonadosomatic indices (GSIs) and the monthly proportion of gonadal stages (established through histology). Fecundity was evaluated by counting macroscopically hydrated oocytes. The reproductive season of G. maculatus in the population assessed extended from March through November (the more protracted for the species described so far). The GSI was higher in males than females, with maximum individual values occurring at the final maturation stage. The simultaneous presence of postovulatory follicles and developing oocytes indicates iteroparity. Our results suggest lower instantaneous investment in reproduction at the individual level but a more prolonged throughout the year than other populations of the species, even under more extreme winter conditions. Considering the increased reproduction costs under extreme habitats and based on our findings, we suggest how populations from the same geographic area can deploy different strategies to cope with energy trade-offs. These results highlight the importance of integrated physiological and ecological approaches to elucidate the basis for variation in life-history traits.