In territorial species with polygynous mating systems, reproductivesuccess reflects phenotypic variation. At the gross level, suchphenotypic variation can include that of body size and weaponmorphology, 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 jawsof males function as a weapon in fights, to test the hypothesis thatweapon performance (i.e., bite force) is a better predictor of fitnessthan body size and weapon size.
The study finds that bite-force performance was a strong predictorof reproductive success. However, no size measure was correlated withany estimate of mating success or with potential reproductive output.These results counter the conventional wisdom that bigger is alwaysbetter, and they support the hypothesis that weapon performance, whichis likely to directly influence fight outcomes, has far strongereffects on fitness than size.
The strong influence of weapon performance on reproductive successsuggests that selection acts on weapon performance, which in turndrives the evolution of weapon morphology. As such, the use ofmorphology as a proxy for performance and its presumed extensions tofitness should be based, whenever possible, on empiricalmorphologyperformance relationships.
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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 theCollared Lizard (Crotaphytus collaris)" 166:3 September 2005.
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