Browsing by Author "Telford, Steven"

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    Communication and sexual selection in the barking gecko (Ptenopus kochi)
    (1997) Polakow, Daniel Adam; Jarvis, Jenny; Cherry, Michael; Telford, Steven
    This study focused on elucidating the functional significance of some aspects of the behaviour of Koch's barking gecko, Ptenopus kochi, during a field season conducted at the Desert Ecology Research Unit in Namibia for four months in 1995. Ptenopus kochi is a terrestrial species, and males were observed calling from their burrow entrances in the dry Kuiseb river bed during the hot summer months. First, aspects of competition among calling males were investigated. Calling males were seen to be non-randomly distributed relative to one another with evidence for regularity of spacing in dense aggregations. Sound intensity was investigated as the mechanism of spacing, and was mathematically modelled to gauge how the intensities of the calls of nearest-neighbour males overlapped. Results revealed a constancy at which neighbouring call intensities overlap, and playback experiments ratified the presence of a critical intensity threshold in the population, beyond which male tolerance broke down. These results suggested that spacing in P. kochi is vocally-mediated and that sound intensity acts as the proximate cue through which individuals gauge the closeness of neighbouring males. Second, the inter-relationships between call features of P. kochi's vocalisation, and how these features related to both intrinsic (morphological) and extrinsic (ambient) sources of variability were analytically explored. The principles of information theory and individual recognition by voice were used to gauge the variation manifest in the features of P. kochi's call. A novel statistical method for disentangling the influence of incidental sources of variation from 'signal' features in animal voices was developed. Results showed how once the predictable covariance in call structure was removed, the calls of P. kochi males were rendered statistically indistinguishable from one another. Several descriptor measures of P. kochi's vocalisation were seen to be highly dependent on meteorological determinants, as was nightly chorus duration. Lastly, mate-choice in P. kochi was explored using correlational evidence. Results revealed that mating success was closely linked to individual male differences in display effort and chorus site burrow activity, and less to morphological or territorial characteristics. Counter-intuitively, a positive relationship between call rate and chorus site residency was found in males, suggesting a possible role for classical condition-dependence in the evolution of female mate preference. Aspects of mate choice, together with the emergent importance of residency in this study were discussed and some ideas suggested for further research.
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    Mating dynamics of South African forest millipedes : Centrobolus (Diplopoda: Pachybolidae)
    (1998) Cooper, Mark Ian; Telford, Steven; Nicolson, Sue W
    This study focuses on the mating dynamics of South African forest millipedes Centrobolus (Diplopoda: Spirobolida: Pachybolidae). The main objectives were to investigate the two most common mechanisms of sexual selection, sperm competition and cryptic female choice. The approach was to (1) quantify sexual dimorphism and find the selection pressures operating on the sexes, (2) determine the functional significance of male and female genitalia, (3) understand why there should be a conflict of sexual interests in prolonged copulations, and (4) resolve the mechanisms of sperm competition and cryptic female choice by comparing male mating strategies and sperm precedence to female mating strategies and sperm usage. All hypotheses tested in this thesis are centered on whether there is a conflict of interests between the sexes.
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    Sex in southern african spirostreptida millipedes : mechanisms of sperm competition and cryptic female choice
    (1997) Barnett, Mandy; Telford, Steven; Nicolson, Sue W; Brown, Alec C
    Spirostreptida millipedes comprise three families, the Harpagophoridae, Spirostreptidae and Odontopygidae. They are polygynandrous. Males transfer sperm via species-specific accessory genitalia called gonopods, that comprise three components, two of which, the emote and telopodite, are involved in processes of sperm transfer. The emotes function to translocate ejaculates from the penes to the vulvae, where they are stored. A delay between insemination and fertilisation provides an arena for syn- and postcopulatory sexual competition. These operate at the gametic level via sperm competition and cryptic female choice. By combining studies of genital form and function with single and double mating experiments, this study elucidates these processes in some southern African Spirostreptida millipedes.