Survival after heat shock (heat-shock resistance) in selection and control lines was measured at generation 11.
Previously, several authors revealed effects of density on heat-shock resistance, but their studies yielded conflicting results.
based on an analysis of several Drosophila species, Levins (1969) reported higher heat-shock resistance in larger flies compared to smaller ones reared at the same density.
In the present work, we revealed no direct association between knockdown resistance and heat-shock resistance estimated as the proportion of flies that survived after exposure to a potentially lethal temperature.
Here we provide results for selection on heat-shock resistance in the cactophilic Drosophila, Drosophila buzzatii, which inhabits necrotic cladodes of Opuntia cactus, generally in hot and sun-exposed environments (Barker and Mulley 1976), with temperatures in the cladodes at noon commonly exceeding 37 [degrees] C (Krebs and Loeschcke 1994).
Heat-shock resistance of adults was measured after 17 selection generations in the adult selection lines, and separately, after 19 generations in the larval selection lines.
Heat-shock resistance of larvae was measured the same selection generation as that for adults in the larval selection lines, and both in the same and the prior generation for the adult selection lines.
- After 17 generations of selection on heat-pretreated individuals [ILLUSTRATION FOR FIGURE 1 OMITTED], heat-shock resistance was significantly higher in selected lines than in control lines, which received pretreatment each selection generation but were not otherwise exposed to stress (selection effect, [F.sub.1,2] = 73.6, P [less than] 0.05).
- Differences in larval heat-shock resistance among selection and control lines were examined twice in the adult selection lines [ILLUSTRATION FOR FIGURE 2 OMITTED].