2b) Fertility after adult heat-stress
Adult males were given an initial group of virgin females to mate with, and there was no interaction between stress temperature and hardening treatment on immediate fertility of adult males (χ2(1) = 0.244, p=0.621; Figure 2b, days 13-19). We also found no effect of heat-stress on immediate fertility (χ2(1) = 2.286, p=0.130; Figure 4, days 13-19), and no main effect of hardening on fertility at this initial time point (χ2(1) = 0.590, p= 0.443; Figure 2b, days 13-19).
From 7 days post heat-stress onwards in non-hardened flies, there was no interaction between heat-stress and time (χ2(1) 3.333, p=0.068; Figure 2b, days 19-27). However, we found that heat stress significantly reduced fertility through a main effect of stress (χ2(1) = 28.444, p< 0.001; Figure 2b, days 19-27). Stressed males had lower fertility than controls after 7 days post heat-stress. We found no significant effect of time on fertility after day 7 (χ2(1) = 2.413, p= 0.120; Figure 2b, days 19-27) meaning fertility remained low post 7 days.
There was no interaction between hardening and time on fertility at the stress temperature of 34°C when measured after day 7 (χ2(1) = 2.1824, p= 0.140; Figure 2b, days 19-27). Hardening also did not affect fertility of heat-stressed adults (χ2(1) = 0.1319, p= 0.717; Figure 2b, days 19-27) meaning hardening does not change the sterility pattern induced by thermal stress, even though there was a main effect of time on fertility (χ2(1) = 4.265, p= 0.039; Figure 2b, days 19-27), where fertility increased slightly as the experiment progressed.