Survival and Lt50 after exposures at constant low temperature were compared to the values obtained at alternating temperatures in two active (summer acclimated) temperate terrestrial arthropods. The experimental regimes used interruptions - daily transfers from the lower temperature to various higher temperatures for two hours or to one high temperature for Various durations. In both species the alternating conditions improved survival, implying reparation of the chill injury. In the collembolan Orchesella cincta, there was a maximum Lt50 when the higher exposure temperature was equal to the temperature of rearing (19°C). In the bug Pyrrhocoris apterus, Lt50 increased strongly with increasing higher temperature from 0 to 15°C, and was subsequently constant over the entire physiological range suitable for development (to 35°C). Exposure at 0°C was harmful if continuously applied, but survival increased, relative to a constant exposure at -5°C, if the temperature alternated between -5 and 0°C., Zdeněk Hanč, Oldřich Nedvěd, and Lit
Genetic variation for thermal plasticity plays an important role in the success or failure of a species with respect to the colonization of different thermal habitats and the ability to deal with climatic change. The aim of this paper is to study the relative contribution of the additive and non-additive components of genetic variation for the slope of the temperature reaction norm for juvenile growth rate in the springtail Orchesella cincta. We present the outcome of an artificial selection experiment for steep and flat temperature reaction norms and the results of a parent-offspring heritability experiment. There was a considerable phenotypic variation for the slope of the reaction norm. The selection experiment and the offspring to parent regression analysis, however, yielded no evidence for significant additive genetic variance. There were also no indications for maternal effects. The full-sib analysis, on the other hand, revealed a significant broad sense heritability of 0.76. An unforeseen result was that the slopes of females were steeper than those of males. This influenced the broad sense heritability of the full-sib analysis, since accidental female or male biased broods inflate the estimate of heritability. A randomization test showed that the probability level of the observed "between group" variance on the basis of the sexual differences alone was less than 10-5. From this we conclude that autosomal genetic variation played its own separate role. In conclusion, the thermal reaction norm for growth in juvenile O. cincta is not very much determined by the additive effects of a large number of independent genes, but more likely based on a still unknown but mainly non-additive, partially sex-related genetic mechanism, possibly including both dominance and epistatic effects. Hypotheses about the role of phenotypic plasticity in processes of local adaptation and speciation should thus be alert to such a complex genetic architecture.