Similar fertility losses in response to heat are followed by distinct recovery trajectories across seven Drosophila species

Abstract

Heat-induced sterility is widespread across ectotherm species, yet its underlying mechanisms remain poorly understood. In mated females, thermal stress can disrupt female reproductive physiology while also affecting sperm stored within the reproductive tract, making the mechanisms of fertility loss difficult to distinguish. Here, we investigated the extent and recovery dynamics of female heat-induced fertility loss across seven Drosophila species. We tracked fertility after acute heat exposure, tested whether remating restored fertility, quantified stored sperm in two closely related species, and examined whether reproductive thermal sensitivity covaried with adult heat tolerance. We found that heat exposure reduced egg-hatching success in all seven species, but recovery differed among species. Fertility recovered within several days in most species, whereas D. simulans showed persistent declines and D. melanogaster showed limited recovery. Remating restored or maintained fertility in both species. Stored sperm declined through time in both D. simulans and D. mauritiana, but D. mauritiana retained more sperm at later sampling points, consistent with their contrasting patterns of fertility decline and maintenance. Across species, greater adult heat tolerance was associated with smaller immediate reductions in fertility, but not with cumulative reproductive loss across subsequent days. Together, these findings show that similar initial fertility losses can lead to markedly different recovery trajectories and highlight the importance of comparative, multi-species approaches that integrate female physiology, sperm-storage dynamics, mating behavior, and whole-organism thermal tolerance when assessing reproductive resilience to climate warming.