Fertility loss and recovery dynamics after repeated heat stress across life stages in male Drosophila melanogaster: Patterns and processes

Frequent and extreme temperatures associated with climate change pose a
major threat to biodiversity, particularly for organisms whose metabolism
is strictly linked to ambient temperatures. Many studies have explored
thermal effects on survival, but heat-induced fertility loss is emerging
as a greater threat to population persistence. However, while evidence is
accumulating both juvenile and adult stages heat exposure can impair
fertility in their own ways, much less is known about the immediate and
longer-term fitness consequences of repeated heat stress across life
stages. To address this knowledge gap, we used male Drosophila
melanogaster to investigate (i) the cumulative fitness effects of repeated
heatwaves across life stages, (ii) the potential of recovery from these
heat-exposed, and (iii) the underlying mechanisms. We found individual and
combined effects of chronic juvenile and acute adult heat stress on male
fitness traits. These effects tended to exacerbate over several days after
brief heat exposure, indicating a substantial fertility loss for these
short-lived organisms. Our findings highlight the cumulative and
persistent effects of heat stress on fitness. Such combined effects could
accelerate population declines, particularly in more vulnerable species,
emphasizing the importance of considering reproduction and its recovery
for more accurate models of species persistence.