Male alternative reproductive strategies are found in some species of most major animal taxa, but are especially widespread in fishes. Mature males of the shortfin molly, Poecilia gillii, display extensive variation in size and morphology. We devised a field test of a priori hypotheses regarding the interrelationships between male size, colouration, morphology, and mating tactics. Males did not occur in discrete size classes, but instead occurred in a size and morphological continuum. Large males exhibited...