Abstract
dc:description.abstractInvasive species threaten global food security and biodiversity. The process of biological invasion often results in secondary contact between closely related taxa, producing ‘experiments in evolution’. Evolutionary genetics can be used to study invasive species and inform their management. In this thesis I focus on noctuid crop pests in the genus Helicoverpa, which are among the most economically significant agricultural pests in the world. Helicoverpa armigera was first reported as an invasive species in Brazil in 2013, where it hybridized with its native sister species Helicoverpa zea. The two species diverged in allopatry ~1.5–2 million years ago and show strong but incomplete prezygotic reproductive isolation. As a consequence of hybridization, an allele conferring insecticide resistance was introduced into the native Brazilian H. zea population through adaptive introgression. I use this as a system with which to investigate the outcome of secondary contact between native and invasive species. In Chapter 1, I assess the utility of population genomics for the study of invasive species in general, specifically considering the use of whole-genome resequencing data. In Chapter 2, I apply these principles to a study of native H. zea in North America. I reveal genomic signatures of selection at two cytochrome P50 genes associated with pesticide resistance: one rose quickly in frequency over a ~20-year period through strong selection on intraspecific variation, and the other was introduced from South American H. armigera via introgression. In Chapter 3 I focus on the admixed population of Helicoverpa in Brazil using a whole-genome resequencing dataset collected over a ten-year time series from the earliest detected non-native sample. I show that although the two species have remained distinct in sympatry, in part due to genetic incompatibilities distributed throughout the genome, occasional hybridization has resulted in substantial interspecific gene flow. Hybridization resulted in the bidirectional exchange of fitness-enhancing resistance alleles between native and invasive pests. In Chapter 4 I reveal that a viable population of H. armigera has recently established in North America, at Chicago O’Hare Airport. The founders of this population were likely introduced directly from South America. Despite a detectable demographic bottleneck, the newly established population shows high genetic diversity because of inherited introgressed H. zea alleles. Thus, hybridization during the initial incursion into Brazil may have reduced the probability of inbreeding depression during a secondary introduction in North America. In this system, hybridization and adaptation have interacted to shape the outcome of a biological invasion. The spread of H. armigera occurred not only through direct establishment, but also through the spillover of fitness-enhancing alleles into native H. zea populations. Thus, a “genic” view of biological invasion has revealed otherwise cryptic evolutionary dynamics, with implications for ongoing monitoring and management. The results presented here demonstrate that evolutionary genomics is a valuable tool in invasion science, and that biological invasions are powerful systems with which to investigate contemporary evolution. The study and management of invasive species is strengthened through the integration of biological perspectives and disciplines.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2024
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- North, Henry
- Advisor dc:contributor.advisor
-
- Jiggins, Chris
Subjects
dc:subject × 9Rights
dc:rightsIdentifiers
dc:identifier.*- Author Identifier
- 0000-0002-8773-2428
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/378304