Fig. 4. Acquired thermotolerance of mature Leghorn individuals following a single embryonic heat exposure. Presented is the expression of HSP90 in the brain tissue. Actin levels were used to detect equal amounts of loaded proteins. Control, not exposed to heat as embryos; 6d, exposed to heat (6 h at 42°C) on day 6 of incubation; C, unexposed mature individuals (5 months of age); HS, heat exposure at maturity (8 h at 40°C during two consecutive days). Percentage survival (at the bottom of the figure) was not affected by the embryonic heat exposure (unpaired t-test, P=0.34) and is expressed as means ± S.D. (N=19).