Abstract

The fruit fly Drosophila melanogaster and the baker’s yeast Saccharomyces cerevisiae are
classic research model organisms that are also associated in nature, at least around vineyards.
Sharing the same ephemeral fruit niche, winged Drosophila feed on immotile yeasts. That a
yeast diet is essential for larvae development, and that saprophagous fruit flies are attracted to
a suite of yeast volatiles, has been well established over the last century. Recently, research
has focussed on the potential mutual benefit of this interaction hypothesising yeasts also
benefit via dispersal from ephemeral fruits. It now appears that the concept of a co-evolved
mutualism between yeasts and Drosophila has permeated the literature. However, until robust
evidence regarding the evolution and maintenance of this yeast-fly association has been
provided, we suggest there is no compelling evidence to reject the more simplistic null
hypothesis that these interactions are due to exaptation, and not a mutualism driven by natural
selection.