Adaptive Ratiation &
Functional Morphology

The Salmon Forest Project
Molecular Studies
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Geographical variation and asymmetry of predator defences in threespine stickleback (Gasterosteus aculeatus ) of the Queen Charlotte Islands.

Carolyn A. Bergstrom Ph.D.

    Threespine stickleback have undergone a massive adaptive radiation among freshwater habitats on the Queen Charlotte Islands during the last 12,000 years.  My Ph.D. project has focussed on fine-tuning our understanding of the causes of geographical variation in the predator defense structures of stickleback. 

    Bilateral asymmetry in structural defences of stickleback from these islands demonstrates immense variation from one lake to the next.  My research has looked at the functional implications of asymmetry in the context of the predator/prey interaction.  I am interested in whether asymmetry in some traits is more detrimental than in others, and whether variation in how selection acts on asymmetry is reflected in geographical patterns of morphology.   Stickleback from lakes dominated by predatory trout have considerably less asymmetry in their defence structures than stickleback from bird-dominated lakes.  This suggests that diving bird predation does not select against defensive asymmetry as strongly as trout predation does, and that asymmetry in functional traits may be used as an indication of the history of the intensity of trait-specific natural selection in wild populations.

    In addition to asymmetry, I am also interested in how structural defences affect swimming performance in stickleback.  While previous work has shown that large fish predators select for increased robustness of stickleback defences, my work has provided support for the hypothesis proposed by Dr. Reimchen that diving birds select for structural defence reduction.  My experiments have demonstrated improved swimming performance in stickleback with fewer lateral scutes, making them more likely to outswim a pursuing diving bird.