Fertility loss under thermal stress

Climate change models predict that the frequency and intensity of
heatwaves are likely to increase, therefore understanding population
responses to these extreme climatic events will be key in mitigating
biodiversity loss. Here, using the male dimorphic bulb mite, Rhizoglyphus
robini, we investigate and compare the impact of experimental heat stress
on survival and fertility between females and male morphs that differ in
the expression of a sexually selected weapon. We show that lethal limits
are similar among all individuals, but find clear sex differences,
although no difference between morphs, in sub-lethal temperatures causing
sterility: female fertility remains high close to lethal limits, whereas
both male morphs suffer fertility loss at more than 2.5°C below their
lethal limits. Contrastingly, when thermal stress was lower, the sexes and
morphs do not differ in their thermal sensitivity and declines in
reproductive output are comparable, these declines appear to be additive
as we observe the greatest declines when both sexes were exposed to
thermal stress. In addition, during assays, we included an extra treatment
that allowed individuals two extra days to recover and found that
fertility loss was almost fully recovered when thermal stress was low, but
only partially recovered under the most extreme temperatures. The impact
of heat stress on fertility therefore appears to be temporary with
individuals rapidly recovering: whether recovery can negate negative
population level effects remains to be investigated. Our experiments
reveal the impact of heat stress on survival and fertility, finding
sex-specific fertility loss under the most extreme thermal conditions.