Gregory F. Grether

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Life history traits in guppies (Poecilia reticulata) vary geographically along a predator assemblage gradient, and field experiments have indicated that the association may be causal; guppies introduced from high predation sites to low predation sites have evolved the phenotype associated with low predation in as few as seven generations. It has long been(More)
Under the indicator models of mate choice, female preferences evolve to exploit the condition-dependence or "indicator value" of male traits, which in turn may cause these traits to evolve to elaborate extremes. If the indicator value of a male trait changes, the payoff function of the female preference for that trait should change and the preference should(More)
Carotenoid-based sexual coloration is the classic example of an honest signal of mate quality. Animals cannot synthesize carotenoid pigments and ultimately depend on dietary sources. Thus, in carotenoid-poor environments, carotenoid coloration may be a direct indicator of foraging ability and an indirect indicator of health and vigour. Carotenoid coloration(More)
Colour patches are complex traits, the components of which may evolve independently through a variety of mechanisms. Although usually treated as simple, two-dimensional characters and classified as either structural or pigmentary, in reality colour patches are complicated, three-dimensional structures that often contain multiple pigment types and structural(More)
A central question in the evolutionary diversification of large, widespread, mobile mammals is how substantial differentiation can arise, particularly in the absence of topographic or habitat barriers to dispersal. All extant giraffes (Giraffa camelopardalis) are currently considered to represent a single species classified into multiple subspecies.(More)
Carotenoids produce most of the brilliant orange and yellow colours seen in animals, but animals cannot synthesize these pigments and must rely on dietary sources. The idea that carotenoids make good signals because they are a scarce limiting resource was proposed two decades ago and has become the leading hypothesis for the role of carotenoids in animal(More)
I studied the sex-limited red spots on the wings of male rubyspot damselflies (Hetaerina americana) in relation to territoriality and fitness in the wild. Both observational and experimental (wing spot manipulation) studies indicated that wing spots were selected through competition among males for mating territories, not through female choice or direct(More)
Rarely are the evolutionary origins of mate preferences known, but, recently, the preference of female guppies (Poecilia reticulata) for males with carotenoid-based sexual coloration has been linked to a sensory bias that may have originally evolved for detecting carotenoid-rich fruits. If carotenoids enhance the immune systems of these fishes, as has been(More)
The extent to which interspecific interference competition has contributed to character evolution is one of the most neglected problems in evolutionary biology. When formerly allopatric species come into secondary contact, aggressive interactions between the species can cause selection on traits that affect interspecific encounter rates (e.g. habitat(More)
In most animals, the origins of mating preferences are not clear. The "sensory-bias" hypothesis proposes that biases in female sensory or neural systems are important in triggering sexual selection and in determining which male traits will become elaborated into sexual ornaments. Subsequently, other mechanisms can evolve for discriminating between high- and(More)