Fig. 2. Effect of species, parental genotype and pre-treatment (PT) on (A) basal and (B) inducible thermotolerance. Data for D. lummei strain 200 and D. virilis strain 9 are replotted from Garbuz et al. (2002). In B, two-headed arrows represent the change in thermotolerance from basal levels (broken lines) to tolerance after PT (solid lines). In pretreated D. virilis strain 9 (solid red), PT was 30 min at 35°C, 36°C or 37°C. In pretreated D. lummei strain 200 (solid blue), PT was 30 min at 35°C (as shown), 36°C (not shown) or 37°C (not shown). No D. lummei pre-treated at 36°C or 37°C survived the ensuing heat shock. The inset indicates color coding for reciprocal hybrids of D. lummei strain 200 and D. virilis strain 9 and the species identity of female (F) and male (M) parent. Broken and solid lines indicate thermotolerance with and without pretreatment, respectively, after 35°C PT for 30 min. Hybrids also underwent PT at 36°C for 30 min with heat shock either following immediately (triangles) or 3 h later (squares); these symbols signify the LT₅₀s.