The main aims of this thesis are to firstly determine the genetic mating system in a
little studied New Zealand passerine, the tūī, Prosthemadera novaeseelandiae.
There is a paucity of data on the genetic mating systems of the honeyeaters, thus this thesis will make a significant contribution to furthering our knowledge of honeyeater life histories. Secondly, I aim to advance the knowledge of the adaptive function of female genetic polyandry, and the role of sexual selection in the evolution of male secondary sexual characters. Although there has been much research conducted on sexual selection and the adaptive significance of extra-pair paternity over the past two decades, the hypotheses are still contentious and no consensus has been reached. The tūī is particularly suitable for assessing these
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hypotheses as they possess some intriguing sexually dimorphic characteristics and behaviours that are not normally associated with monogamy. Thus the tūī may provide us with valuable information of the evolution and maintenance of mixed reproductive strategies. I achieve this by examining the role of male phenotypes in male mating success, and the fitness consequences to females of mating with males possessing certain genotypic and phenotypic traits.
This thesis comprises four research chapters (Chapters 3 to 6) with an introductory (Chapter 1), methods (Chapter 2) and concluding (Chapter 7) chapter. This thesis is concerned with the subject of sexual selection and fitness consequences of female mate choice and thus some of the theories and conclusions explored in these chapters invariably overlap and resulted in some unavoidable repetition. For this reason each chapter should be considered with respect to the preceding and following chapters. Every effort has been made to limit duplication where appropriate, and therefore a chapter describing the genetic methodology has been included.
Chapter 1 provides a general overview to the theories explored in this thesis. A background to extra-pair paternity is given and current theories that have been proposed to explain the adaptive significance of extra-pair paternity are detailed. A background to general sexual selection theory and its role in the evolution of male sexually selected traits is presented. I also summarise the current published
literature on the life histories of the study species and the Meliphagidae family.
Chapter 2 details the methodology used to develop and amplify microsatellite markers for the tūī that are used in every chapter of this thesis. This chapter was published as a paper: S. J. Wells, W. Ji, S. M. Baillie, and D. Gleeson (2013).
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Characterisation and cross-amplification of fourteen microsatellite loci for the New
Zealand endemic tūī (Meliphagidae), Prosthemadera novaeseelandiae. Conservation
Genetic Resources 5: 113–116.
Chapter 3 examines the rate of extra-pair paternity and SSD in a wild population of tūī at Tawharanui Regional Park. I first review the current evidence for selection pressures, acting via extra-pair paternity, on the evolution of sexual size dimorphism in birds. I then investigate this in the tūī by assigning genetic parentage to offspring, and examining male within-pair and extra-pair paternity success in relation to male phenotypic and genotypic characteristics in a population where a significant proportion of the candidate males were sampled. This chapter has been published as a paper: Wells S.J., Ji W., Dale J., Jones M. B., and Gleeson D. (2015) Male size predicts extra-pair paternity in a socially monogamous
bird with extreme sexual size dimorphism. Behavioral Ecology 26 (1): 200-206
Chapter 4 assesses the importance of direct and indirect benefits in female mate choice in the tūī. I draw on the outcomes of male mating success in the previous chapter and investigate the benefits that these males may provide for offspring survival and offspring reproductive value (measured as offspring sex) as two common proxies of offspring fitness. I determine whether these males provide direct or indirect benefits by disassociating the benefits provided by social and
genetic fathers. This chapter is currently being submitted to the journal Animal
Behaviour.
Chapter 5 investigates whether EPP has led to the selection for alternative male reproductive strategies in the tūī. I examine this by determining whether males of differing phenotypic quality invest differentially in parental effort. As parental care
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has not been studied in tūī, I firstly quantify two measures of male and female provisioning as proxies for relative parental effort. I then apply these rates to test various sexual selection hypotheses that predict the parental effort of male and female parents in response to male quality and reduced average certainty of paternity as a consequence of EPP.
Chapter 6 provides insight into nestling growth rates in tūī and examines offspring growth, as an important proxy of fitness, in relation to female mate choice. First, nestling growth rates and size at hatching are quantified and the hypothesis of sex-specific growth rates due to SSD in tūī is investigated. Second, I determine the effect of male and female provisioning rates on offspring growth. Third, I examine whether females gain direct or indirect benefits from mate choice that influence offspring growth and size at hatching by comparing traits of the social and genetic fathers and within-pair and extra-pair maternal half-siblings. Chapter 7 concludes by summarising findings from each research chapter and integrating them into a general framework. I consider these findings in relation to current sexual selection hypotheses and discuss my conclusions on the adaptive significance of male secondary sexual characters and extra-pair paternity in tūī. I outline the novel contribution that this thesis has contributed to these theories and suggest priorities for future research.
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