Influences of Atmospheric Ethanol on AdultDrosophila mojavensis:Altered Metabolic Rates and Increases in Fitness among Populations

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Abstract
Adult Drosophila mojavensis are exposed to low-molecular-weight volatiles produced by fermenting tissues, "rots, " of several columnar cacti endemic to deserts of Mexico and Arizona. Because these cactus tissues lack carbohydrates required for adult survival, volatiles have been hypothesized to be sources of energy. Extension of adult longevity in 4% ethanol versus water vapor under starvation conditions and in thepresence of fermenting cacti used in nature for feeding was determined in a system designed to avoid hypercapnic side effects common to many studies. Adults from a mainland population survived longer in 4% ethanol vapor than adults from a Baja population, with females always living longer than males under starvation conditions. No carryover of stored metabolites derived from ethanol vapor was detected under starvation conditions. Metabolic rates, estimated by study of oxygen consumption in a closed system, were higher in ethanol vapor than in water vapor. Significant amounts of metabolites were recovered in body tissues and as respired carbon dioxide in radioisotope studies. Ethanol vapor also increased lifetime fecundity but had no effect on age at first reproduction. Ability to survive and reproduce in low-molecular-weight volatile-rich, carbohydratepoor cactus environments has allowed D. mojavensis to colonize extensive desert regions now within their species range.