Browsing by Subject "vision"

Now showing 1 - 2 of 2
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    Host-Parasite Arms Races and Rapid Changes in Bird Egg Appearance
    (2012) Spottiswoode, Claire N; Stevens, Martin
    Abstract Coevolutionary arms races are a powerful force driving evolution, adaptation, and diversification. They can generate phenotypic polymorphisms that render it harder for a coevolving parasite or predator to exploit any one individual of a given species. In birds, egg polymorphisms should be an effective defense against mimetic brood parasites and are extreme in the African tawny-flanked prinia (Prinia subflava) and its parasite, the cuckoo finch (Anomalospiza imberbis). Here we use models of avian visual perception to analyze the appearance of prinia and cuckoo finch eggs from the same location over 40 years. We show that the two interacting populations have experienced rapid changes in egg traits. Egg colors of both species have diversified over time, expanding into avian color space as expected under negative frequency-dependent selection. Egg pattern showed signatures of both frequency-dependent and directional selection in different traits, which appeared to be evolving independently of one ano...
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    Worms, frogs, crabs, and the Eye of God: Mpondo and Hlubi perceptions of white malevolence and surveillence
    (Taylor & Francis, 2011) Blackbeard, Susan I
    This paper extends the debate on black-perceived white supernatural powers in the late nineteenth and early twentieth-century Eastern Cape, South Africa – a conversation initiated by Sean Redding, and developed further by Clifton Crais, whose main contention has been rebutted by Jeff Peires. Having briefly considered their claims, this paper examines, first, Western Mpondo perceptions of missionaries' extraordinary or supernatural powers by focusing on a dream/vision of herdboys, and second, a claim that the amaHlubi in the Matatiele district ceased resistance to dipping owing to fear of white supernatural powers. Finally, I show how, in different ways from those described by Redding and Crais, these powers were perceived by various groups, and counteracted or exploited.