Influence of dietary yeasts on Drosophila melanogaster life-history traits

An organism's fitness is highly dependent on resource quality. The diet of saprobiotic organisms often comprises a variety of microorganisms. Saprophagous Drosophila melanogaster Meigen (Diptera: Drosophilidae) is known to feed on various yeast species, both as larva and adult. The yeasts encountered by the insects may differ in composition and quality, and thus in their influence on larval and adult performance. Our study explores life-history consequences of larval diet on selected larval and adult traits, as well as larval and adult food choice and egg-laying behaviour. The chosen yeast species could be shown to influence several life-history traits of D. melanogaster, such as survival, development time, and adult body weight. Additionally, the amount of yeast biomass initially fed to the larvae significantly influenced development time and adult body weight, whereby the effect depended on the yeast species offered. There were also yeast-specific influences on the measured fitness traits when larvae were reared at different densities. Larvae exhibited a preference for those yeast species that had shown to favour most of the measured life-history traits. Adults, on the other hand, exhibited a different preference. Contrary to our expectation based on the preference-performance hypothesis, female adult flies did not prefer to lay their eggs on substrates inoculated with yeast species that had been shown to favourably influence larval development time. Possible reasons for this seemingly 'bad mother'-behaviour are being discussed.