UBC Theses and Dissertations
Geographic variation in courtship behaviour of the guppy, Poecilia reticulata Ballin, Peter J.
This thesis attempts to elucidate some adaptive modifications of behaviour in response to environmental influences in geographically isolated populations of the guppy. Poecilia reticulata, Peters, I examined courtship behaviour of ♂guppies from three Trinidad streams which differ in several physical and biotic parameters. Males of two head-stream populations (the Paria and Upper Aripo Rivers) are larger and more brightly colored than ♂♂ of a lowland stream (the Guayamare River). Headstream ♂♂ are more conspicuous in their courtship than downstream ♂♂ in a one ♂ -one ♀ encounter: they exhibit more display behaviour and move around the ♀ more. It was concluded that differences in behaviour are genetic. I then investigated effects of ♂ interactions on courtship. Paria ♂♂ were much more aggressive than Upper Aripo or Guayamare ♂♂ upon encountering other ♂♂of the same race. Increased aggressiveness in P ♂♂ occurred in the presence of ♀♀, suggesting that ♂♂ fight over ♀♀. Display behaviour was reduced (especially in P ♂♂, who fought) when two ♂♂ were introduced to one another and a ♀ after an isolation period. However, no decrease was noted without an isolation period. Display behaviours decreased with the addition of a third ♂ in the Paria and Upper Aripo races, but not in the Guayamare. Increasing the number of ♂♂ generally heightened the level of ♀-oriented activity and reduced the distance between ♂♂ and the ♀. Preferences for fish of the same race occurred. When three ♂♂, one of each race, were presented to a virgin ♀ simultaneously, Paria ♂♂ fought only in the presence of Paria ♀♀, Upper Aripo displays were more successful in eliciting sexual responses, especially from Upper Aripo ♀♀, and Guayamare ♂♂ thrust more at Guayamare. Choice behaviour experiments revealed that virgin Paria and Guayamare ♀♀ respond selectively to ♂♂ of their own race. In another experiment, Upper Aripo ♀♀ responded much more readily to displays from Upper Aripo males. Females seem more likely to complete full sexual responses with ♂♂ of their own race. It appears that relatively light predation and good visibility have resulted in the evolution of displaying and fighting as the primary mating strategies in headstreams. Heavy predation and poor visibility have resulted in selection for downstream ♂♂ which display less frequently and rely more heavily on tactile signals to insure insemination. A simple model is presented to suggest how behavioural differences evolved. The results are discussed in light of other studies on geographic variation in color and mating behaviour.
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