Abstract
Vector-borne parasites often manipulate hosts to attract uninfected
vectors. For example, parasites causing malaria alter host odor to
attract mosquitoes. Here we discuss the ecology and evolution of
fruit-colonizing yeast in a tripartite symbiosis – the so-called
“killer yeast” system. “Killer yeast” consists of
Saccharomyces cerevisiae yeast hosting two double stranded RNA
viruses (M satellite dsRNAs, L-A dsRNA helper virus). When both dsRNA
viruses occur in a yeast cell, the yeast converts to lethal
toxin‑producing “killer yeast” phenotype that kills uninfected yeasts.
Yeasts on ephemeral fruits attract insect vectors to colonize new
habitats. As the viruses have no extracellular stage, they depend on the
same insect vectors as yeast for their dispersal. Viruses also benefit
from yeast dispersal as this promotes yeast to reproduce sexually, which
is how viruses can transmit to uninfected yeast strains. We tested
whether insect vectors are more attracted to killer yeasts than to
non‑killer yeasts. In our field experiment, we found that killer yeasts
were more attractive to Drosophila than non-killer yeasts. This
suggests that vectors foraging on yeast are more likely to transmit
yeast with a killer phenotype, allowing the viruses to colonize those
uninfected yeast strains that engage in sexual reproduction with the
killer yeast. Beyond insights into the basic ecology of the killer yeast
system, our results suggest that viruses could increase transmission
success by manipulating the insect vectors of their host.