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Title: Sperm morphology and fertilisation success in the zebra finch Taeniopygia guttata
Author: Bennison, Clair
ISNI:       0000 0004 5346 3826
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2014
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The aim of this study was to understand how variation in sperm morphology influences sperm swimming velocity, and consequently, the fertilisation success of males in a competitive context. Chapter 2 provides the methods behind the three key aspects underpinning the work described in this thesis. The set-up and maintenance of the selective breeding regime producing the population of zebra finches is described. The procedures involved in the collection of sperm, and assessment of sperm quality are then given in detail. Chapter 3 describes the artificial selective breeding regime, involving the three lines (long, intermediate and short) used to investigate how sperm morphology responds to selection on sperm total length. The tail and total length of sperm respond similarly to artificial selection, with decreasing and increasing lengths observed in the short and long selection lines, respectively. There were differences in the relationships between various sperm components in the three lines, for example midpiece and tail length were positively associated in the short selection line, yet generally, there was a negative relationship between these traits observed across the long and intermediate selection lines. Chapter 4 focuses on the genetic relationships that underpin the phenotypic associations evident in Chapter 3, and how these genetic relationships may determine the evolutionary trajectory of sperm morphology in response to selection. The difference in phenotypic relationships in the short selection line compared to the long and intermediate lines originate from a difference in genetic covariance between the sperm components across the lines. Chapter 5 uncovers the possibility that phenotypic changes in sperm morphology may be constrained by stabilising selection, based on the evidence that increased sperm swimming velocity is associated with absolutely larger component dimensions, but only up to certain values, beyond which swimming velocity declines. Chapter 6 draws together the work carried out through this thesis, and tests the hypothesis that longer, faster swimming sperm have a fertilisation advantage compared to shorter and slower swimming sperm in a competitive situation. There was a strong effect of sperm length on the competitive ability of sperm, but this advantage was mediated by complex interactions between the male and female selection history, and the different relationships that these male - female mating combinations have on the proportions of sperm that finally reach the ovum.
Supervisor: Birkhead, T. R. ; Slate, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available