Abstract
Summary - Eight Indian geographical populations of D ananassae, collected along a 20°N latitudinal range, revealed significant clinal variation at the Adh (alcohol dehydrogenase) locus and Adh allelic frequency increased by about 1.5% with 1° latitude. Latitudinal increase of ethanol tolerance (1.8-3.7%) was observed in adults. Survival studies with adults showed that, in all cases, ethanol was used as a resource at low concentrations, while becoming a stress at higher concentrations. The resource/stress concentration threshold increased from 1.2 to 4% with latitude. Larval behaviour also exhibited an attraction/avoidance threshold, increasing from 1.6 to 4.4% ethanol with increasing latitude of origin. The parallel occurrence of latitudinal variation at the Adh locus and ethanol tolerance and utilisation in natural populations of D ananassae could be maintained by balancing the natural selection, which varies spatially along the northsouth axis of the Indian sub-continent. Drosophila ananassae / Adh polymorphism / ethanol utilisation / larval behaviour 1
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