Life stage-specific effects of heat stress on spermatogenesis and oogenesis in Drosophila melanogaster.

Biodiversity is increasingly threatened by unpredictable, frequent, and intense climatic events like heatwaves that pose harmful impacts on ectotherms. Beyond the health and survival of organisms, reduced reproductive performance has emerged as a critical fitness consequence of thermal stress induced by high temperatures. Many studies on these effects expose organisms to heat stress during the adult stage or throughout development, often focusing on cumulative effects across life stages, and they tend to examine one or the other sex. This approach may not reflect the short-term nature of many extreme heat events and limits our understanding of stage- and sex-specific fitness consequences in short-lived organisms. To address this gap, we used Drosophila melanogaster to investigate the sex-specific reproductive performance following short heat stress of varying intensity at different developmental stages. We found the thermal sensitivity to be higher in males than females, and to increase toward adult emergence, leading to nearly complete reproductive failure and substantially slowed recovery. These results highlight how even brief bouts of heat stress during a sensitive phase could affect population dynamics and persistence. Our findings also underscore that incorporating both sex and life stage could improve predictions of species persistence.