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Bird-associated permanent ectosymbionts examined at coarse and fine scales
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- Author / Creator
- Grossi, Alexandra A.
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All multicellular organisms host one or more species of symbiont. Endosymbionts of homeotherms experience relatively constant environments whereas those of ectotherms and all ectosymbionts experience variation in external environment. For ectosymbionts, both the presence of a host and a compatible external environment are necessary. Permanent symbionts (those with no off-host stages) are typically transferred from parent to offspring or via close contact between host individuals. There has long been an expectation that permanent symbionts should show patterns of genetic diversification similar to the host’s. Using the host/symbiont systems of Rock Pigeons (Columbidae: Columba livia Gmelin) and Ovenbirds (Parulidae: Seiurus aurocapilla [Linnaeus]) and their permanent ectosymbionts (lice and mites), I investigated factors that influence ectosymbiont assemblage and population structure at both broad and fine scales.
To determine diversity of ectosymbionts that infest Rock Pigeons in Canada and whether there are geographic patterns in assemblages (Chapter 2), I sampled pigeons from: Vancouver BC, Calgary AB, Edmonton AB, Saskatoon SK, Winnipeg MB, Southern Ontario, and Halifax NS. I found 13 species of ectosymbionts: three of feather-dwelling mites, three skin mites, two nasal mites, and five feather lice. Only Vancouver and Halifax had all 13 ectosymbiont species, and only five species were found in every sampling location. I statistically assessed relationships between the local environment and the mite and louse assemblages. Annual precipitation, minimum humidity and maximum humidity of the month the pigeon was euthanized explained 10.6% of the variation in mite assemblages; annual maximum temperature, annual minimum humidity, and minimum temperature, and precipitation in the month before the pigeon was euthanized explained 10.7% of the variation in louse assemblages. Based on their more restricted distributions, I conclude that feather mites are more strongly affected by local environment than other ectosymbiont groups, and that humid coastal environments are suitable for more ectosymbiont species than dry continental regions.
Rock Pigeons are non-migratory and are usually restricted to urban centres, suggesting that they should show strong genetic structure, which should be mirrored by their permanent ectosymbionts. In Chapter 3, I assess population structure of Rock Pigeons across Canada together with that of two of their louse species, Columbicola columbae (Linnaeus) and Campanulotes compar (Burmeister). ddRAD sequencing was used for pigeons and mtCOI for lice. Based on ΔK values and DAPC there were three genetic clusters for pigeons: one for Halifax, one for Vancouver and one that included all other sampling locations. The two louse species had different haplotype networks and the genetic structure of C. compar more closely resembled that of its host, matching predictions based on previous studies of its vagility relative to C. columbae. Rock Pigeons may be less sedentary than typically thought, or continuing introductions of Rock Pigeons are obscuring the signal of local differentiation of both bird and symbionts in most Canadian locations.
In Chapter 4, I move from broad- to fine-scale distribution of symbionts on hosts. Infestation parameters of quill mites (Syringophilidae) are rarely examined because this requires dissection of quills. These mites use their long chelicerae to pierce the quill wall to feed on living tissue, and reproduce only inside the quill; therefore, quill wall thickness and quill volume could influence their colonization success. I assessed the distribution of the quill mite Betasyringophiloidus seiuri (Clark) from Ovenbirds from Canada to determine if specific feathers have higher mite prevalences or intensities, and if quill-wall thickness and quill volume vary with either of these infestation parameters. I examined the flight feathers of 21 dead ovenbirds, nine of which proved to be infested with quill mites. Feathers with the highest prevalence were Primaries 1 and 2, and Secondaries 1, 2, and 5. There was a strong positive correlation between quill volume and mean mite intensity. Feathers with quill walls thicker in some areas than the mites’ extended chelicerae had lower prevalences than feathers with walls consistently thinner than the length of the chelicerae.
In summary, I found that aspects of both the ectosymbionts’ immediate habitat, the host, and the habitat of the host can potentially influence their broad- and fine-scale distribution and assemblage structure. However, much of the variation in my results was not explained by the parameters I examined; I recommend manipulative experiments in order to resolve some of the remaining mysteries. -
- Graduation date
- Fall 2020
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.