Spiroplasma infection and tolerance of nematode parasitism in Drosophila

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Most species of insects are infected by symbiotic microorganisms, which spread either by directly benefiting their hosts or by manipulating host reproduction in ways that benefit the symbiont, but not the host. Bacterial Spiroplasma are among the more widespread of these symbionts. All Spiroplasma discovered to date either manipulate host reproduction or are pathogenic to their insect hosts. In populations of the fruit fly, Drosophila neotestacea, Spiroplasma have been found to confer resistance to nematode parasitism. Parasitized flies in the wild are essentially sterilized by the nematode if they do not carry Spiroplasma, but have nearly normal fertility if they are infected with these symbionts. This is the first finding of a beneficial effect of Spiroplasma on any insect species, and the first demonstration of an adverse effect of Spiroplasma on nematodes. Spiroplasma infection in D. neotestacea appears to have increased rapidly in the last 20 years in the eastern US and may be spreading westward. This project will conduct experiments to test for the effect of nematode parasitism on Spiroplasma infection dynamics within populations of D. neotestacea. Reciprocally, the effect of Spiroplasma on nematode parasitism in these flies will also be tested. Although most individuals of D. neotestacea in eastern North America are infected with Spiroplasma, none of the flies west of the Rockies are infected. This project will sample populations in British Columbia and Canadian Prairie Provinces, that were last sampled in 2002, to assess whether Spiroplasma is spreading westward across North America. The fertility-restoring effect of Spiroplasma will also be tested on other combinations of Drosophila and nematode species. If general, such effects could be of great applied significance. River Blindness and Elephantiasis are caused by filarial nematodes that are transmitted by blackflies and mosquitoes. If Spiroplasma confers resistance to filarial nematodes, then Spiroplasma could spread within populations of the insect vectors, which might reduce nematode reproduction and thus incidence and severity of filarial diseases. In principle, a relatively simple manipulation of the insect vectors could yield great public health benefits. This project will provide research training for undergraduate and graduate students.