Ethanol Utilization: Threshold Differences Among Six Closely Related Species of Drosophila.

Abstract

Ethanol vapour in a closed system, containing only ethanol in solution. causes an increase in adult longevity of six melanogaster-group (subgenus Sophophora) species. up to various threshold concentrations where it becomes a metabolic cost rather than a benefit. The threshold ranking, and the ranking for maximum longevity increase compared with controls, is: D. melanogaster > D, teissieri > D. simulans > D, yakuba > D. erecta > D. mauritiana. Offspring were produced at certain ethanol concentrations. usually to the larval stage only. The ranking for the most advanced developmental stage was the same as above. except that D. erecta and D. mauritiana were reversed. The qualitative effect of environmental ethanol on all species is therefore similar. The five species apart from D. melanogaster form a low-threshold group. Of these, D. simulans is a cosmopolitan species which is more tolerant of climatic extremes (especially cold) than the other four (which are tropical). The possibility that low ethanol thresholds are usual in tropical species finds support from latitudinal clines in D. melanogasrer, the tolerance levels of which approach those of the lower threshold group in tropical regions but are much higher (as above) in temperate regions. A need is emphasized for studies on physiological variables of ecological significance on closely related Drosophila species, especially in taxa such as the melanogasrer subgroup. which includes species both restricted and widespread in distribution.