Diet-induced phenotypic plasticity of feeding morphology in the orangespotted sunfish, Lepomis humilis

Generalist fish species often exhibit two or more recognizable morphotypes specialized to exploit a particular habitat and niche. Divergent benthic an d pelagic morphs of sunfish of the North American sunfish genus Lepomis hav e been found in some populations. The proximate cause of this phenomenon is not known. It could be differential survival and habitat segregation among different morphs produced by different genotypes within a species or it co uld be a phenotypically plastic response to environmental influences such a s diet. I tested the hypothesis that variation in feeding morphology (body shape, gill raker and pharyngeal jaw morphology) in the orangespotted sunfi sh, Lepomis humilis occurs in response to diet. Fish were collected as youn g-of-the-year and were reared in individual aquaria and fed three differing arthropod diets. According to a multivariate analysis of covariance on pri ncipal components derived from body truss, gill raker and pharyngeal jaw me asurements, diet significantly affected morphology. Fish that fed on a diet of mealworms developed a significantly more blunt snout based on a least s quares means estimation of component values.