Expression of the heat-shock protein HSP70 in Drosophila buzzatii lines selected for thermal resistance

The level of HSP70 expression induced by a non-lethal high temperature was examined in lines selected for increased thermal resistance and in correspo nding control lines of Drosophila buzzatii, in order to test if selection f or high temperature resistance leads to an increased level of HSP70 express ion. The lines used were selected for up to 64 generations either as adults or through all larval stages. In adult selection lines, hard selection was implemented every second generation after mild heat hardening. In larval s election lines, larvae were exposed each generation to laboratory "natural" selection. Generally lines selected as adults showed a higher HSP70 expres sion than did controls, both in third instar larvae and in adults. A strong negative response to selection of HSP70 expression was found in all lines that were selected at cycling temperatures during larval development. The: results suggests that a trade off between heat resistance in form of HSP70 expression and fecundity/fertility lire responsible For the level of HSP70 expression. The effect of the different methods of selection on HSP70 expre ssion suggests that heat resistance constitutes more than one trait.