Effects Of Heat Stress Expeirences On Life-history Traits In English Grain Aphid (Sitobion Avenae)

By simulating temperature experiences of climate warming: short-time heat exposure, persistenthot days or night warming on hot days within generation, and the altered frequency of hot days inmaternal generation of Sitobion avenae, we investigated the immediate and time-lagged effects of heatstress experiences on the thermal tolerance and life history traits, as well as the consequence ofpopulation dynamics in S. avenae. The main conclusions are as follows:(1) Heat shock at the age with the greatest heat resistance does not mean that there are lessthermal time-lagged effects on other life history traits and population dynamics. The3rd-and4th-instars of S. avenae have the highest upper thermal tolerance. However, they were least able toacclimate (CTmax) in response to high temperatures, suggesting a potential trade-off between basaltolerance and the hardening ability to thermal tolerance. In addition, the time-lagged effects of heatshock at different ages may be trait-dependent. There were significant differences of nymphaldevelopmental times between heat exposure treatments at different age. The most inhibiting effects ondevelopmental time were observed at the first and fourth instars nymphs. But adult traits were affectedmainly by the duration of brief heat exposure. Further, the extent of population parameters reduceddepended on not only the duration of heat exposure but also the age exposed to heat.(2) Continuous hot days occurred at the early stage of nymphs or adult stage play moreimportant roles in population consequences than those occurred at the later stage of nymphs.Effect of high temperatures on nymph duration depended crucially on whether1st-instar stageexperienced hot days. And adult traits were determined largely by duration of hot days. However,nymphal survival depended on both1st-instar stage experienced hot days and duration of hot days.Overall, Continuous hot days occurred at the early stage of nymphs or adult stage play more importantroles in population consequences than those occurred at the later stage of nymphs.(3) Changes of these moderate nighttime temperatures have much biological impact whencombined with hot days. The development rates of nymphs increased with night warming on hot daysduring early or whole stage of nymph and a generation, although the increase of nighttime temperatureduring later stage of nymph did not significantly affect developmental rate. When compared toexpectations based on constant temperatures, night warming raised the optimum temperature fordevelopment by3°C, in contrast to results from experiments where temperature variability was alteredsymmetrically or in a parallel manner. Night warming experiences in whole stage of nymph alsoreduced linearly aphid survival under heat despite of temperatures shifting within a moderate range.Overall, night warming exacerbated the detrimental effects of hot days on the intrinsic rate ofpopulation increase except for any effects of night warming during early stage of nymph beingoverwhelmed by negative impacts of daytime high temperatures.(4) Maternal temperature has significant effects on population performance of offspringreared under high developmental temperature. Maternal temperature experience under continuous hot days affected negatively not only the development and survival of nymph exposed to highfluctuating temperature, but also the prereproductive time and the adult proportion of immediatelybreeding of offspring reared under22℃constant temperature. In addition, maternal high temperatureexperience (continuous hot days or frequent hot days) also affected profoundly fecundity of offspringunder normal fluctuating temperature. Further, both of two maternal patterns of hot days increased thedevelopmental variation of offspring. Although maternal experience of frequent hot days also increasedthe variation of adult traits, the least variation of offspring was observed when mothers were rearedunder continuous hot days. Overall, mediate temperatures of offspring might offset the negative effectsof maternal high temperature experience on population performance. However, maternal hightemperature condition can deteriorated further population consequence of offspring by50%if progenywas continued to be reared under high temperature condition.