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Title: Experimental and Observational approaches to investigating sexual selection in sepsidae (Diptera)
Keywords: Sexual selection, sepsidae, experimental evolution, mating behaviour, cryptic species
Issue Date: 19-Aug-2011
Citation: TAN SIEW HOONG DENISE (2011-08-19). Experimental and Observational approaches to investigating sexual selection in sepsidae (Diptera). ScholarBank@NUS Repository.
Abstract: In this thesis I explore how data from morphology, behaviour and genes for multiple species can reveal new insights into sexual selection including ? how mating behaviour can reveal species limits in cryptic species, the effects of operational sex ratio on the evolution of sexually dimorphic traits and the relationship between mating behavior, male mating costs, and morphological evolution. In the first chapter, I find high genetic divergence within a supposedly `widespread? species Allosepsis indica (Wiedemann, 1824) that indicates the presence of cryptic species. In order to address if multiple species should be recognized within A. indica, I conducted hybridization experiments and identified multiple reproductively isolated populations. I find that DNA sequences very accurately predicted species boundaries whereas morphological characters provided only partial resolution. Due to high population-level variation, courtship behaviour and copulation duration were the least useful traits for resolving species limits. Population dynamics surveys were conducted and these showed that a female-biased sex ratio persisted in lab cultures of Pulau Tioman flies due to significantly shorter male lifespan. I found strong correlations between the operational sex ratio (OSR) of the population and several aspects of mating behaviour (level of male courtship, degree of female resistance and copulation duration). This inspired the experiment detailed in Chapter Two. In the second chapter, I describe an experimental approach towards testing the effects of a female-biased operational sex ratio on male dimorphic traits in Themira superba (Haliday, 1833). For 15 generations, I artificially manipulated the OSR in experimental treatments to be female-biased (6:1), simulating the effects of a Wolbachia infection. As a result of greater mating opportunities and corresponding reduction in the intensity of mate competition, experimental males took longer to complete development and were significantly larger than control males. In addition, the males invest fewer resources into sexually dimorphic structures. I measured five traits - fore-femur complexity, sternite area, clasper area and testes volume, and four were reduced in males from the experimental cultures. A combination of these traits was significantly affected by the treatments. Due to the rapid nature of this change, we predict that Wolbachia infections maybe be an initiator of speciation in sepsid flies. In the third chapter, we reiterate the usefulness of integrative taxonomy (comparative analyses of genes, behaviour and morphology) for resolving species limits in cryptic species. I contributed the reproductive isolation and mating behaviour data that led to the resurrection of Sepsis pyrrhosoma Melander & Spuler, 1917, a species that was previously synonymised with S. flavimana. In the fourth and final chapter, I describe the mating behaviour of Saltella sphondylii (Shrank, 1803) in detail and find five unique elements for this species. This confirmed that mating behaviour is rapidly evolving in Sepsidae. I discuss aspects of this unique mating profile that may contribute to the high male mating costs in this model species. I also provide SEM images of the S. sphondylii male intromittent organ and document structures that imply that Saltella?s intromittent organ is more fragile than the one of other sepsid species.
Appears in Collections:Master's Theses (Open)

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