Vilchez-Ramirez, Igor (2018-08). Exploring The Persistence Of A Non-Male-Killing Spiroplasma Infection In Drosophila And The Potential Host Range Of Drosophila-Infecting Spiroplasmas. Doctoral Dissertation.
Thesis
This work addresses the persistence of a non-male-killing Spiroplasma strain infecting the fly Drosophila hydei under conditions where there are no apparent fitness benefits to the host. This work also addresses the potential host range and the factors affecting those potential host ranges of distinctly related Spiroplasma strains on a group of Drosophila hosts that are distinctly related. We began by exploring if the infection modifies a set of characters in the host as compared to the same characters in uninfected hosts. The characteristics explored were sex ratio, larval stage mortality, longevity and fecundity. These factors were chosen because if modified by the infection, they could promote its long-term persistence. We then reexamined longevity and fecundity and expanded to the exploration of the effect of the infection on age at maturity and preferential mating to infected females by all males. Our results show that longevity and early fecundity are affected by the infection, with infected females having a higher early fecundity and shorter life-span than uninfected ones; together, these factors can promote the long-term persistence of the infection. These results suggest that fitness effects have to be reexamined on other host-parasite pairs where no benefits to the host seem to occur along with the long-term persistence of parasites. We also report the results of the potential host range experiments, for which we cross-infected 5 Spiroplasma strains into each other's 5 natural Drosophila hosts, generating 25 pairs of infections. The Rohde Index was used to evaluate the host range. The factors evaluated for their effect on host ranges were parasite and host phylogenies, intrinsic host and parasite characteristics, and the interaction of all of these factors. The potential host ranges of Spiroplasma strains are varied and not predictable simply based on phylogenetic relatedness of either bacteria or host. Only the host and parasite intrinsic characteristics and their interaction were found to affect the infection success rate of Spiroplasma when introduced to new and old hosts.
