Morphological and life-history differentiation between littoral and pelagic forms of pumpkinseed

Trophically dimorphic pumpkinseed populations were investigated in five lakes in Ontario, Canada to determine: (1) whether the morphological traits that distinguish littoral from pelagic forms are consistent among populations; (2) whether the pharyngeal Jaw apparatus is diminished in pelagic pumpkinseeds because of a lower proportion of hard-bodied prey in their diets (3) whether there is life-history differentiation between littoral and pelagic forms. Pumpkinseeds captured from the littoral and pelagic zones differed significantly in morphology in four of the five lakes, but the number of external measures that differed significantly within the differentiated populations ranged from zero to six. Littoral pumpkinseeds generally had longer heads. more rearward placement of dorsal and pectoral fins, longer pectoral fins and deeper bodies than pelagic pumpkinseeds. Littoral and pelagic pumpkinseeds were more readily differentiated by internal morphometric measures. with littoral individuals having larger molars and wider spacing between gill rakers than pelagic individuals. Littoral and pelagic differences in age at maturity. size at maturity and gonado-somatic index were present only in one of three populations assessed for these traits, Suggesting that morphological divergence is not necessarily accompanied by life-history differentiation. (C) 2003 The Fisheries Society of the British Isles.