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Sexual conflict and secondary sexual traits in West Australian Riffle Bugs (Insecta: Hemiptera: Veliidae). An overview of the relationship between morphology and behaviour

Maroni, Paige (2017) Sexual conflict and secondary sexual traits in West Australian Riffle Bugs (Insecta: Hemiptera: Veliidae). An overview of the relationship between morphology and behaviour. Honours thesis, Murdoch University.

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How and why an animal chooses its mate is characteristic of morphological and behavioural adaptations developed to maximize reproductive success. This thesis compares patterns of sexual dimorphism (through micro-CT analyses) in three Veliidae species (Microvelia oceanica, Nesidovelia peramoena and N. herberti) and aims to explain these in the context of sexual conflict. Sexually antagonistic morphological and behavioural traits were also of interest and were documented through examinations of male-female reproductive interactions of N. peramoena via video recordings and micro-CT scan outputs of interlocked pairs, frozen in copula. Interlocked pairs were captured through a new technique for snap freezing surface dwelling insects, which was developed within this thesis. In all three species, females were found to be generally larger than males and macropters larger overall than apters, as is often the case with insects. All specimens examined were documented to express some form of a secondary sexual trait which are likely to be coevolving in an evolutionary arms race. In females, these resistance traits variously included connexival convergence, genital concealment and setal tufts. Females of N. peramoena showed strong pre-mating resistance behaviours evidenced by either fleeing or vigorously struggling during 96% of all observed intersexual interactions. In both Nesidovelia species, males expressed persistence traits such as a ventral abdominal process on segment 8 and ventral abdominal segment 7 medial concavity. Through this study, these traits are now known to act as a pregenital clamp grasping to the females on the underside of her proctiger during the pre-mating struggle, as well as during copulation. Interestingly, while macropterous males retain their secondary sexual traits, macropterous females were found to lack their putative resistance traits, suggesting either an energetic or mechanical trade-off in development. This study is one of the first to provide evidence that sexual conflict is the likely driving force behind the behaviours and sexual dimorphism in the Veliidae. The array of different secondary sexual traits makes those in the Gerridae (the current model group for sexual conflict and sexually antagonistic character studies) seem tame in comparison. Within these riffle bug species, unique coevolved male-female grasping and anti-grasping structures provide strong evidence for sexual antagonism in veliid mating that have not previously been documented in any surface dwelling insects.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Bryant, Kate and Tatarnic, Nikolai
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