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Drosophila fruit flies are some of the most common visitors to mushrooms in temperate forests and are
commonly infected with obligate nematode (worm) parasites. Female nematodes infect Drosophila larvae
feeding inside mushrooms, and produce juvenile nematodes, which are shed by adult flies as they visit
new mushrooms. There is striking variation in many aspects of this host-parasite association, such as
nematode host range and virulence, with some hosts rendered completely sterile upon infection. Our
long-term interests include understanding the causes and consequences of this variation, the role of
parasites in contributing to species differences, and the genetic basis of insect resistance to nematodes.
Many animals and plants harbour microbial symbionts that help protect them against natural enemies, and
these defensive symbionts are increasingly recognized as major players in the ecology of species interactions.
In collaboration with John Jaenike (U Rochester) and his lab, we recently discovered a novel defensive
symbiosis involving Drosophila neotestacea, and a strain of Spiroplasma. Drosophila neotestacea is commonly
infected with a virulent nematode (worm) parasite, Howardula aoronymphium, and until recently, almost all
infections resulted in complete sterility. We have found that the obligate endosymbiont Spiroplasma appears
to completely restore fertility to flies that are infected with nematodes. While the mechanism of defense is
not currently known, worms in Spiroplasma-positive flies are about half the size. Evidence also suggests that
Spiroplasma infection frequencies have recently increased, and that Spiroplasma infections are spreading across
North America. We are actively monitoring this spread and are interested in its long-term consequences. We are
also interested in understanding the mechanism of defense, and in understanding interactions between the host
immune system, symbionts, and natural enemies. Our long-term goals are to understand the costs and benefits
of symbiont-encoded versus host-encoded defense.
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