ALFARO, M.E.*; BOLNICK, D.I.; WAINWRIGHT, P.C.; , ; , ; , ; , ; , ; Washington State; Univ. Texas, Austin; UC Davis: Evolutionary consequences of redundant design in labrid fishes

Many physiological traits consist of two hierarchically related levels: physical structures, and the emergent functional properties of those structures. Because selection tends to act on the emergent functional traits, the evolution of structural phenotypes will depend on the nature of the form-function relationship. Complex physiological or biomechanical traits are often characterized by many-to-one mapping: numerous structural phenotypes can yield equivalent functions. We suggest that this redundancy can promote the evolution of phenotypic diversity, and illustrate this effect with a combination of empirical and analytical studies of a complex biomechanical trait, the four-bar linkage found in the jaws of labrid fishes. We show that labrid jaw mechanics are subject to many-to-one mapping of form to function, but that some functions have higher levels of morphological redundancy than others. This variation in redundancy has affected the diversity and distribution of labrid jaw shapes: labrid species are disproportionately concentrated around functional traits with higher potential for redundancy. Many-to-one mapping can also mitigate evolutionary constraints imposed by functional trade-offs, by allowing a species to simultaneously optimize multiple functional properties of the labrid jaw four-bar system. Finally, we illustrate how our model can be used to study the influence of historical contingency on the evolution of form. We test the hypothesis that the shape of presumed ancestral jaws explains derived jaw shapes across functional shifts using empirical examples within labrid fishes. Many-to-one mapping may be an important factor in generating widespread biological patterns such as uneven physiological diversity among clades, morphological convergence, and historical contingency of form.