Genetic variation in thermal tolerance among natural populations of Drosophila buzzatii: down regulation of Hsp70 expression and variation in heat stress resistance traits

Summary

• 1
   Thermal adaptation was investigated in the fruitfly Drosophila buzzatii Patterson and Wheeler. Two natural populations originating from a high- and a low-temperature environment, respectively, were compared with respect to Hsp70 (heat shock protein) expression, knock-down resistance and heat shock resistance.
• 2
   Three main hypotheses were tested: (i) The expression level of Hsp70 in flies from the high-temperature habitat should be down-regulated relative to flies from the colder habitat. (ii) Flies having higher Hsp70 expression levels should be weakened most by a hardening treatment and go faster into coma, as Hsp70 level reflects stress intensity, and therefore display reduced heat knock-down resistance. (iii) Heat shock resistance should be increased in the population with highest Hsp70 expression because the level of Hsp70 is positively associated with this trait.
• 3
   The results generally matched the hypotheses. Hsp70 expression was reduced in the high-temperature population. Knock-down resistance was higher in the high-temperature population and survival after heat shock was lower in the high-temperature population.
• 4
   This study showed genetic differences in thermal tolerance between populations, indicating that high temperature in nature may be an important selective factor. Moreover, knock-down resistance in this study seems to be a more relevant trait than standard heat shock resistance for identifying thermal adaptation in natural populations.