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In territorial species with polygynous mating systems, reproductive
success reflects phenotypic variation. At the gross level, such
phenotypic variation can include that of body size and weapon
morphology, as well as of weapon function and performance.
In a study published in the September issue of The American Naturalist, A. Kristopher Lappin (Northern Arizona University) and Jerry F. Husak (Oklahoma State University) use the eastern collared lizard (Crotaphytus collaris ), a sexually dimorphic lizard in which the jaws of males function as a weapon in fights, to test the hypothesis that weapon performance (i.e., bite force) is a better predictor of fitness than body size and weapon size.
The study finds that bite-force performance was a strong predictor
of reproductive success. However, no size measure was correlated with
any estimate of mating success or with potential reproductive output.
These results counter the conventional wisdom that bigger is always
better, and they support the hypothesis that weapon performance, which
is likely to directly influence fight outcomes, has far stronger
effects on fitness than size.
The strong influence of weapon performance on reproductive success suggests that selection acts on weapon performance, which in turn drives the evolution of weapon morphology. As such, the use of morphology as a proxy for performance and its presumed extensions to fitness should be based, whenever possible, on empirical morphologyperformance relationships.
Sponsored by the American Society of Naturalists, The American Naturalist is a leading journal in the fields of ecology and evolutionary biology and animal behavior. For more information, please see our website: www.journals.uchicago.edu/AN
A. Kristopher Lappin (Northern Arizona University) and Jerry F. Husak (Oklahoma State University), "Weapon Performance, Not Size, Determines Mating Success and Potential Reproductive Output in the Collared Lizard (Crotaphytus collaris)" 166:3 September 2005.
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