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theses

The label ‘invasive’ is most often applied to exotic species that have established and spread, frequently becoming so abundant that they have negative impacts on humans and ecosystems. Understanding what factors promote invasiveness may allow us to better manage the impacts of exotic species. In my dissertation I strive to elucidate ecological and evolutionary processes responsible for the success of an emerging invasive mosquito, Aedes japonicus japonicus, a cold-adapted species from Asia with established populations in Europe, North America, and surprisingly, in sub-tropical Hawaii. In Chapter 1, I report the results of laboratory experiments examining the interactions between larvae of Ae. j. japonicus and another invasive mosquito, Culex quinquefasciatus, and associated microbial fauna. In a high temperature experiment, Ae. j. japonicus only survived when Cx. quinquefasciatus, a tropical and pollution-tolerant species, was present. Treatments with Cx. quinquefasciatus contained significantly lower numbers of a protozoan flagellate that is potentially toxic to Ae. j. japonicus. From these findings I speculate that some invasive mosquitoes can ameliorate habitat conditions allowing other species to exploit new geographic areas and microhabitats, the first time that facilitation between mosquitoes has been proposed. In Chapters 2 and 3, I describe the genetic structure of Ae. j. japonicus across elevational gradients in Hawaii and Virginia, respectively. In Hawaii, populations at warmer low elevations display signatures of bottlenecks, including lower genetic diversity and greater genetic differentiation, which support the findings from Chapter 1 that this species survives poorly at warm temperatures. In Virginia, I also observed elevational differences in genetic patterns consistent with temperature-mediated selection, though frequent long-distance dispersal events (probably human-mediated transportation along roads) augment genetic diversity within low elevation populations. In summary, I postulate that Ae. j. japonicus has profited from habitat amelioration by co-occurring mosquitoes and from long-distance transport by humans. In fact, I hypothesize that humans have driven the post-establishment evolution of invasiveness in this mosquito, both by increasing genetic diversity though population admixture and by exposing it to novel selective pressures. These results underline the importance of preventing multiple introductions and restricting gene flow between exotic populations in order to limit their evolutionary potential.

ETD_5408

Ph.D.

Includes bibliographical references

by Andrea M. Egizi

doi:10.7282/T3Q23XK7

ETD doctoral

The author owns the copyright to this work.