Are contest-related trait exaggeration and intrasexual dimorphism evolutionarily correlated across harvestman species?

Abstract Exaggerated male traits used in intrasexual contests are often condition dependent and, in many taxa, intrasexual dimorphism in these traits arise in association with alternative reproductive tactics. Although it is frequently assumed that trait exaggeration and intrasexual dimorphism evolve in concert, this hypothesis has not yet been tested within a comparative framework. Here, we investigate whether the degree of exaggeration of contest-related traits is evolutionarily correlated with intrasexual dimorphism across species of Neotropical harvestmen. We focus on two subfamilies of Gonyleptidae—Goniosomatinae and Mitobatinae—in which males use extremely elongated legs as threat devices during ritualized contests. Using morphological data from individuals representing 46 species, we quantified leg exaggeration as relative leg length and estimated the degree of intrasexual dimorphism using bootstrap-supported mixture models. We then applied phylogenetic comparative analyses in a Bayesian framework to test for correlated evolution between these traits. In Goniosomatinae, we detected moderate positive phylogenetic correlation between leg exaggeration and intrasexual dimorphism. In contrast, no evidence of correlated evolution was found in Mitobatinae, where many species exhibit pronounced leg exaggeration without intrasexual dimorphism. Together, these patterns suggest that although trait exaggeration may be a necessary condition for the evolution of intrasexual dimorphism, it is not sufficient on its own. Instead, the macroevolutionary association between trait exaggeration and intrasexual dimorphism appears to depend on functional constraints, behavioral flexibility, and the genetic architecture underlying condition-dependent trait expression.