The shape, size and number of sperm males produce and the characteristics of the reproductive tract through which they must travel have been shaped by a multitude of evolutionary forces. The selective pressures acting on sperm and the female tract have produced a wide variety of forms, some of which are unusual to the point that they appear maladaptive. This thesis uses a range of behavioural, physiological, morphometric and theoretical techniques to investigate the evolutionary causes and consequences of non-fertile sperm and spermicide in the Drosophila obscura species group. The primary aim of this thesis is to determine the adaptive significance of the non-fertile 'parasperm' found throughout this taxon. Parasperm have been proposed to perform a number of functions including depressing female remating behaviour and transferring nutriment, but support has not yet been found for any existing hypothesis. Similarly, many roles for spermicide have been proposed, but its adaptive significance and prevalence remain unknown. Chapter 1 discusses concepts and empirical results relevant to the background of the thesis. I first introduce a new hypothesis proposing that selection on males to mitigate the effects of spermicide can lead to the evolution of parasperm (chapter ' 2). This hypothesis is mathematically investigated and its predictions determined. I also review the previously undeveloped hypothesis that parasperm evolved in response to cryptic female choice.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:485876 |
| Date | January 2008 |
| Creators | Holman, Luke |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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