Temperature‐induced changes in spider mite fitness: offsetting effects of development time, fecundity, and sex ratio

Abstract

Abstract Temperature affects many life history parameters in poikilotherms. Temperature clearly affects development time and fecundity, which affect the intrinsic rate of increase. In haplodiploid mites, ambient temperature may also affect offspring sex ratio which, in turn, affects intrinsic rate of increase. The combined effect of all these processes determines the fitness of individual females. However, sex ratio also affects mating structure and, potentially, rate of local adaptation. We investigated the direct effect of temperature variation on sex ratio, development time, and fecundity in the twospotted spider mite ( Tetyranychus urticae ), and calculated the effect of their interaction on mite intrinsic rate of increase. We conducted experiments at 2 temperatures and designed the experiment to separate pre‐adult and adult sensitivity to temperature variation. Mites were reared from eggs to adult ecdysis at either 22 °C or 32 °C. Upon emergence as adults, these 2 groups were each split between 22 °C and 32 °C and allowed to oviposit. Not surprisingly, development from egg to adult was accelerated when mites were exposed to the higher temperature during offspring development, regardless of the temperature experienced by the mother during her development. Fecundity and the proportion of female offspring were affected by temperature only when mothers were exposed during both development and oviposition. About 12 offspring were gained and female bias was increased by 26% when the mother's development occurred at 22 °C, whereas oviposition at 22 °C added only 6 more offspring and increased female bias by only 7%. There was no correlation between sex ratio and fecundity; both were related to temperature but not to each other. Furthermore, development time, not fecundity or sex ratio, appeared to the main factor affecting the intrinsic rate of increase. Our results support other evidence that sex ratio varies independently of development time and fecundity.