Abstract
Heat waves are considered to pose a greater risk to arthropods with their limited thermoregulation abilities than the increase of mean temperatures. Theoretically, within- and trans-generational modifications may allow populations to keep pace with rapidly occurring heat waves. Here, we evaluated this assumption using individuals of predatory mite Amblydromalus limonicus from the F1 and F2 generation, which were exposed to summer or simulated heat wave conditions during juvenile development. Independent of generation, survival and male body size were insensitive to heat waves. Heat stress elongated juvenile development of F1 males and females, and lowered the F1 female size at maturity indicating non-adaptive within-generational effects. Trans-generational modifications speeded up the development of F2 males and females and resulted in larger body size of F2 females deriving from the heat wave-experienced F1 generation. Faster F2 development should be adaptive, because it reduces the exposure time to heat waves and promotes an early beginning of mating activities. Being large at extreme high temperatures maybe a benefit for the F2 females, because large individuals are less vulnerable to dehydration and overheating. Thus, the potential fitness loss from reduced F1 growth should be compensated by increased fitness in the F2 indicating adaptive trans-generational modifications.
Highlights
Heat waves are considered to pose a greater risk to arthropods with their limited thermoregulation abilities than the increase of mean temperatures
Female, but not male body size, decreased, when the juveniles were exposed to heat wave conditions (Fig. 2)
The observed shifts in our experiments in relation to age and size at maturity in a terrestrial arthropod, the predatory mite A. limonicus, caused by temperature could be affected by selective mortality, because these two traits are partially genetically determined[43]
Summary
Heat waves are considered to pose a greater risk to arthropods with their limited thermoregulation abilities than the increase of mean temperatures. Even when the daily mean temperatures are still within a suitable thermal range, a single aberration beyond their critical thermal maxima can be fatal[11] These rapid thermal changes are considered to have stronger effects on survival, development and reproduction of arthropods than small shifts in mean temperatures[12,13]. The time frame for effective genetic adaptations, is significantly shorter for populations exposed to rapidly occurring heat waves than to the slow increase of the mean temperatures, which should make plastic modifications more likely[8,9]. Thermal TGP may allow populations with short generation times to keep pace with rapidly changing thermal conditions under heat waves by phenotypic modifications in a temporally adequate manner[8,16]. Plastic modifications to heat shocks reduced maternal fecundity, but increased the offspring heat resistance in the springtail Orchesella cincta L.19
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