" Nuchal humps, crests, combs, horns or gibbosities occur in the predorsal region of many kinds of bony fishes, usually on top of the head. The role of such humps, when dimorphic, has been suggested in a few instances but never tested. We explored the function of the nuchal hump in a Nicaraguan cichlid fish, ‘Cichlasoma’ citrinellum. In nature, the male develops a modest hump only when ready to mate; it never becomes as large as in well-fed captive males. We entertained two sets of hypotheses, non-communicatory and communicatory, to explain the hump. Based on information about behaviour and natural history, we rejected the non-communicatory hypotheses, which were fat storage, mechanical advantage in a fight, improved hydrodynamics and anti-predation. Among the communicatory hypotheses, we favoured a supernormal-stimulus response, suggesting inter- and intra-sexual selection. We also considered recognition of sex and species, as indicated by a unimodal response by females or an inverse supernormal response by males. We tested these hypotheses by presenting to male and to female subjects four dummies whose nuchal humps varied from none to medium to large to huge. The results were interpreted in light of additional information about natural history. The hypothesis of sex recognition is the most parsimonious. If sexual selection is operating, it would be a unique case of conflicting sensory filters: one would favour an enlarged hump that indicates male fitness, opposed by another filter that discriminates against a yet larger hump that interferes with species recognition "
Clasificación: Comportamiento, Centro y norte -américa.