Reduced Survival Expectancy Weakens Reproductive Isolation Between Annual Fishes Garcialebias reicherti and G. charrua.

Hybridization depends on reproductive isolation, which can be impacted by mate choice. Mate choice may vary temporally, as it is modulated by several factors, including survival expectancy and future opportunities for reproduction. Garcialebias reicherti and G. charrua are annual fishes with parapatric distributions that hybridize in the overlapping area of their distributions. They inhabit temporary ponds that flood during the autumn and dry out during the spring, resulting in decreased survival expectancy and future opportunities for reproduction during the breeding season. We predicted that a decrease in survival expectancy would promote reproduction and reduce reproductive isolation between G. reicherti and G charrua. By simulating desiccation in the early and late breeding season, we investigated the effects of the desiccation risk and the phase of the breeding season on reproductive isolation and reproductive effort of these species. As expected, our findings reveal that decreased survival expectancy influences both reproductive isolation between G. reicherti and G. charrua, and their reproductive effort. Notably, reproductive isolation between these species decreased under a high desiccation risk and in the late breeding season. Additionally, we observed an increase in the frequency of mating and courtship events and aggressive behaviours in the late breeding season. Our study suggests that reproductive isolation between G. reicherti and G. charrua and their reproductive effort can change rapidly within a short period of time, emphasizing the influence of survival expectancy on the temporal dynamics of reproductive isolation and hybridization.