The Evolutionary Ecology of Parasitic Strategies: Experimental Evolution with a Facultatively Ectoparasitic Mite

• Author / Creator

  Durkin, Emily

• Although parasitism is a ubiquitous lifestyle, little empirical evidence exists for how and why parasitism evolves from free-living lineages. Analysis of phylogenetic relationships among taxa that exhibit a range of lifestyles has aided in the development of a commonly proposed hypothesis for the evolution of parasitism: that transient host-associations served as evolutionary stepping-stones towards more obligate parasitism. Using the facultatively parasitic mite, Macrocheles muscaedomesticae, I performed experiments to generate empirical evidence for how free-living organisms evolve parasitic strategies. I successfully artificially selected mites for increased infectious tendency to attach to (infect) Drosophila hydei hosts and estimated the additive genetic variation in the trait to be 16.6%. To learn more about how variation in infectious behaviour is maintained in these mites, I investigated the presence of evolutionary trade-offs (i.e. costs) associated with infectious behaviour. I compared the fecundity, longevity, motility and morphology of mite selected for increased infectious behaviour to unselected control mites. Mite fecundity and longevity were assayed in the presence or absence of a fly host to test for context-dependent trade-offs. I found that regardless of the selection treatment, female mites that attached to a fly produced significantly more nymphs, which provided evidence for the benefits of parasitic behaviour. However, I did not find any evidence for negative trade-offs (i.e. costs) associated with increased infectious behaviour. I then measured the plasticity of infection in selected and control mites to determine whether my directed selection on infectious behaviour caused genetic assimilation (i.e. a loss in plasticity). Contrary to my prediction, the selected mites maintained their infection plasticity despite my direct selection. Lastly, I investigated the biology and life history of M. muscaedomesticae in the context of other published studies, and compared the weights of mites that had and had not previously attached to fly hosts to learn more about whether these mites are merely phoretic on their Drosophila hydei hosts. The mites used in my experiments exhibited similar life-histories to those from other published studies. The female mites that attached to fly hosts indeed weighed significantly more than the mites that did not, but definitive evidence of fluid transfer from fly to mite is necessary to confirm the parasitic nature of M. muscaedomesticae. My research provides experimental evidence for one of the assumptions of the hypothesis that facultative parasitism serves as an evolutionary stepping stone to obligate parasitism. However, it also illustrates the importance of variation in infectious strategies in these mites, which was maintained even in the selected populations. I propose future research to investigate the presence of phenotypic plasticity across multiple parasitic taxa to determine its importance in the evolution of parasitism from free-living ancestors. A better understanding for how parasitisms evolve is critical to developing effective control programs for medically and economically relevant parasites in our changing world.

• Subjects / Keywords

  • Mite
  • Parasitism
  • Evolution
  • Ectoparasite

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-k4et-c285

• License

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