Abstract:

A series of temperature shift experiments have been conducted with homo and/or hemizygous strains for temperature sensitive (ts) mutations of the discless, dl^ts in Drosophila virilis Sturt, where the restrictive temperature is 31℃, and the permissive temperature is 25℃. The temperature threshold is set at 29℃ and fluctuates between 25℃ and 31℃ at an interval of 2℃. The temperaturesensitive period (TSP) is determined by the analysis of both shift up and shift down experiments. Discrete TSPs for lethality are localized on the first, the second and the third larval instar for a 10 hr period after pupation with an interval of a few hours between TSP and the lethal phase (LP). TSPs for adult morphology defects are localized on the second, the third larval instars and the early pupal period. Animals during TSPs are subjected to 12 hr pulse, 24 hr pulse, and 48 hr pulse treatments respectively, and have produced a large number of defects. The defects include: eye scar, clumping pigment eye, small and lozenge shaped eye, missing facets, small wing, thick wing vein, shortened tarsal segments, fused leg segments, extra macrochaetae or bristles, missing antennal segments, and duplicating palpus and/or lacinia, with distinct patterns of eye, wing, bristle and leg defects observed within the third larval instar. Homoeotic mutants also occur in this period. Each defect has its own specific timedependent pattern. The patterns of damage are observed in imaginal tissue and all the defects are categorized into three classes: repeat, deletion and repeat and deletion happened at the same time. There is evidence from genetic somatics that there are some specific time patterns for dl^ts to produce the pleiotropic effects.
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Key words: Drosophila virilis, imaginal disc, temperaturesensitive period, lethal phase, pattern formation