Natural thermal stress and heat‐shock protein expression in Drosophila larvae and pupae

Abstract

Summary 1.Whether Drosophila larvae and pupae naturally experience temperatures that can cause heat damage or death is poorly understood, but bears directly on numerous investigations of the thermal biology and heat-shock response in Drosophila. Accordingly, the temperatures of necrotic fruit, which Drosophila larvae and pupae inhabit, the temperatures of larvae and pupae outside the laboratory, and the levels of the heat-shock protein hsp 70 expressed by larvae in nature were examined. 2. When necrotic fruit was sunlit, internal temperatures rose to levels that can harm indwelling insects. Fruit size and evaporative water loss affected these temperatures. Temperatures of larvae and pupae in the field commonly exceeded 35°C, with living larvae recorded at > 44°C and pupae at > 41°C. Natural mortality was evident, presumably because of heat. 3. In the laboratory, these temperatures kill larvae rapidly, with LT 50 s (time taken for half the sample to be killed) of 30 min at 39°C, 15 min at 40°C and 8·5 min at 41°C. Gradual transfer from 25°C to these temperatures resulted in no lesser mortality than did direct transfer. 4. Hsp 70 levels in lysates of whole larvae were measured by ELISA (enzyme-link immunosorbent assay) with an hsp 70-specific antibody. For larvae within necrotic apples experimentally transferred from shade to sun and within necrotic fruit in situ, hsp 70 levels equalled or exceeded levels detected in parallel laboratory studies of whole larvae or cells in culture. 5. These data provide an ecological context for studies of thermal stress and the heatshock response in Drosophila that has heretofore been lacking.

Sexual Selection Fails to Promote Adaptation to a New Environment

“…The temperature treatment used in this experiment was clearly stressful and within the range encountered by D. melanogaster in nature (Feder et al 1997). Natural clines of thermal adaptation have also been found in this species (James and Partridge 1995).…”

“…Lowgrade thermal stress was chosen for two reasons. First, studies of natural populations indicate that it is a common source of selection (James and Partridge 1995;Feder et al 1997). Second, a large number of loci are simultaneously selected for alternative alleles, thereby substantially increasing the heritable variation in condition.…”

Predatory cannibalism in Drosophila melanogaster larvae

“…Furthermore, in addition to energy and protein, cannibalized conspecifics may be a source of limiting elements such as sodium 7 , which is scarce in fruits. However, even though cannibalism is facilitated in mixed-age groups, which commonly occur in nature 43,47 , the lower natural densities mean that encounters between larvae, and thus opportunities for cannibalism, are presumably much less frequent. Wandering larvae may also have greater chances of escape in nature than in laboratory cultures.…”

Partial thermoregulatory compensation by a rapidly evolving invasive species along a latitudinal cline

“…First, D. subobscura evolving by laboratory natural selection at different constant temperatures have not evolved the expected shifts in inversion frequencies or in wing size (Santos et al 2005). Second, the role of temperature as a selective agent in nature is rarely implicated (Feder et al 1997a, Hoffmann et al 2003, Loeschcke and Hoffmann 2007. Third and most importantly, latitudinal variation in body temperatures (T b ) of Drosophila has always been assumed, but never quantified.…”