Causes and fitness consequences of telomere dynamics in a wild social bird
Wood, Emma Mary
Thesis or dissertation
University of Exeter
This thesis is available for Library use on the understanding that it is copyright material and that no quotation, figure, or illustration from the thesis may be published without proper acknowledgement.
Reason for embargo
I wish to publish papers using material that is substantially drawn from my thesis
Telomeres are increasingly used as biomarkers of somatic maintenance and could conceivably play a causal role in life history trade-offs. In this thesis, I use longitudinal telomere measures from a wild population of cooperatively breeding white-browed sparrow weavers (Plocepasser mahali) to further our understanding of the causes and fitness consequences of individual variation in somatic maintenance, with particular focus on hitherto unexplored effects of the social environment. In Chapter 2, I start by investigating the key prediction of life-history theory that shortfalls in somatic maintenance in early life entail later-life costs, and find supporting evidence. Nestlings with higher within-individual rates of telomere attrition show reduced survival to the following season, even after controlling for the effects of variation in body mass. In Chapter 3, I then investigate the effects of the social and abiotic environment on nestling telomere length and attrition rates and find the first support, to my knowledge, for the key prediction that helpers in cooperatively breeding societies alleviate telomere attrition rates in growing offspring (consistent with the expectation that helper contributions to nestling feeding relax resource allocation trade-offs in offspring). In addition, I find that rainfall prior to egg-laying has a positive effect on hatchling telomere length; an effect that most likely arises via egg- or incubation-mediated maternal effects. In Chapter 4, I investigate the causes of variation in telomere attrition rates in adults, and while there are no overall differences in telomere length or long-term within-individual telomere dynamics between dominant and subordinate birds, my findings are suggestive of dominance-related differences in the short-term regulation of telomere length. In addition, and in concordance with predictions of life-history theory regarding trade-offs between somatic maintenance and reproduction, I find that annual rainfall (a proxy for reproduction-related activity during the breeding season) negatively predicts the within-individual rate of change in telomere length in adults specifically over the breeding season; there was no such relationship in the non-breeding season. Finally, in Chapter 5, I investigate the extent to which natural variation in oxidative state predicts variation in within-individual rates of change in telomere length over time. This chapter provides evidence suggestive of associations between oxidative state and telomere dynamics in a natural population, and highlights complexity in the nature of these relationships. Together my findings provide novel support for key predictions of life-history theory regarding the causes and consequences of variation in somatic maintenance, and lend strength to the view that longitudinal field studies of telomere dynamics can offer useful insights in this regard. Furthermore, my findings highlight the potential for diverse effects of the social environment on patterns of somatic maintenance, and specifically hitherto unexplored downstream effects of helping behaviour on later-life performance and ageing trajectories.
PhD in Biological Sciences