The Critical Impact of Sub- and Supraoptimal Temperatures on Male Fertility Potential of an Invasive Fruit Fly.

In insects, thermal fertility limits have a narrower tolerance range than survival. Therefore, deciphering these critical limits is crucial for understanding population dynamics during or after harsh winter or summer periods. Here investigated the impact of temperature on male fertility in the invasive pest, . We assessed both developmental and postemergence temperatures, using a range of 11 temperatures from 10°C to 30°C and varying chronic exposure durations. The results revealed asymmetrical thermal performance curves for male fertility, with thermal fertility limits (TFLmin and TFLmax) between 9.8°C and 29°C for developmental temperatures and between 10.05°C and 34.8°C for adult temperatures. Males developed at sub- or supraoptimal temperatures were sterile at emergence, and no recovery occurred if the temperature was maintained. Males developed and maintained at supra-optimal temperatures were more sensitive than those exposed to supra-optimal conditions only during the adult stage, highlighting the cumulative effects of thermal stress across life stages. Supra-optimal temperatures only at the adult stage induced some sterility in initially fertile males after a few days, whereas males exposed to suboptimal temperatures never reached fertility, remaining sterile throughout the experiment. Males that underwent winter-like cold-acclimation were in reproductive quiescence and progressively regained fertility when transferred to 20°C. Morphometric analyses of reproductive organs showed that cold-acclimated winter males had anatomical traits similar to the controls after 12 days of recovery. Despite this, mating tests indicated that cold-acclimated males were less attractive to females, suggesting a cost on reproductive potential. This study defines the thermal limits for male sterility under chronic exposure and highlights a partial recovery of fertility in cold-acclimated winter males. It thus provides key insights into the population dynamics of after winter.