Phenotypic plasticity occurs when individual organisms alter their phenotype in response to some external environmental cues. One way that the yeast, Saccharomyces cerevisiae, responds to environmental variation is by forming spores under crowded conditions and resource depletion. It is believed that spores have greater resilience in punitive environments compared to that of the metabolically active vegetative cell, and this may contribute to increased dispersal when ingested by insects. The role of the insect’s own biochemistry may also play a role in differential yeast survivorship. Male and female Drosophila melanogaster are comprised of different digestive biochemistries in their respective digestive tracts. We used the fly Drosophila melanogaster to explore the ecological conditions that favor sporulation as a dispersal mechanism. To determine the role of D. melanogaster sex in yeast survivorship, we exposed yeast to male and female fly treatments, using wild strains from five different global regions. We counted colonies of fluorescent yeast following passage through the fly gut to ensure that only surviving, viable cells were counted. We estimated the fly sex-specific and yeast strain-specific relative survivorship of spores as compared with vegetative cells. We additionally looked for evidence of an interaction between these two variables affecting yeast survivorship.
S. cerevisiae were fed to male and female flies separately to assess the yeast survivorship capabilities and to quantify the number of yeast that survived in males and females, respectively. Preliminary data comparing the survivorship of both vegetative and sporulated forms of yeast across five regions indicated higher mortality of all cells passing through the guts of male flies. While strains varied in the degree to which sporulation improves survivorship, spores were overall more resistant to insect passaging than were vegetative cells. We also found that while fly sex affects yeast survivorship, strain regionality plays a larger role. The phenomena of differential microbial survival based on the sex of the vectoring host may have important implications regarding community dynamics of microbial communities that rely on insects to disperse particularly in parthenogenic insect species or insect species with division of labor by sex. Because the sex ratio of foraging flies is expected to be environmentally dependent and variable, the interaction of insect sex and strain specific differences in yeast may play an important role yeast mortality when it experiences insect gut vectored dispersal.