Mitochondrial heteroplasmy in Australian native bee Amphylaeus morosus and its association with the parasite Wolbachia

Author: Olivia Davies

  • Thesis download: available for open access on 6 Sep 2024.

Davies, Olivia, 2021 Mitochondrial heteroplasmy in Australian native bee Amphylaeus morosus and its association with the parasite Wolbachia, Flinders University, College of Science and Engineering

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Mitochondrial heteroplasmy is the occurrence of more than one type of mitochondrial DNA (mtDNA) within a single cell or individual. It is reported haphazardly across animal taxa (and other multicellular life), but little is known about its origins or functions in an evolutionary context. Conducting a comprehensive literature review of mitochondrial heteroplasmy in animals revealed patterns in type and prevalence in some taxon groups. Ubiquitous heteroplasmy (where all individuals sampled were heteroplasmic) occurred most frequently in arthropods, but occurrences are documented across multiple phyla. I examined mitochondrial heteroplasmy in the mt-COI gene of the native bee species Amphylaeus morosus (Hymenoptera: Colletidae). Every individual sampled (n = 73) across its ~2,000 km range along Australia’s eastern coast was heteroplasmic, with all individuals possessing the same two mitochondrial haplotypes. Next-generation sequencing results found variable nucleotide sites throughout the entire mitogenome, indicating the conserved presence of two distinct mitochondrial lineages (heteroplasmy). Furthermore, A. morosus was consistently infected with two supergroup A strains of the common insect endosymbiont, Wolbachia (Rickettsiales: Anaplasmataceae). I have proposed that consistent heteroplasmy in this species is maintained by a mutualism with co-inherited Wolbachia strains, as both types of genomes follow the same maternal-inheritance pathway. Wolbachia is known to cause selective sweeps on host mitogenomes, resulting in an overall lack of mtDNA variation in host populations. To explore this relationship further, I assessed the feasibility of traditional antibiotic treatment in this non-model host, to apply to investigations of the changes to mtDNA inheritance, post- Wolbachia infection. Although the infection was not completely removed within one generation, one of the Wolbachia strains showed consistent susceptibility to antibiotic treatment. Finally, to investigate whether the mtDNA uniformity across the A. morosus distribution was reflected in the nuclear DNA, genome-wide single nucleotide polymorphisms (SNPs) were generated for individuals across the bees’ distribution using the DArTseq™ platform. Analyses produced strong evidence of genetic clustering between locations (and potential population structure), as opposed to a single, large population as would otherwise be suggested by the conserved mtDNA. This, in combination with habitat modelling showing well-connected habitats before European settlement, provide further evidence that the lack of mtDNA diversity is because of a past Wolbachia-induced selective sweep and not a population bottleneck. This analysis provides further, but indirect, evidence that Wolbachia has played a key role in the evolution of this host’s unusual mtDNA traits.

Keywords: Hymenoptera, mitochondrial heteroplasmy, endosymbiont, population structure


Thesis type: Doctor of Philosophy
Completed: 2021
School: College of Science and Engineering
Supervisor: Michael Schwarz