Stereotyped feeding behaviors of polyphenic bluegill sunfish

Abstract

AbstractPolymorphic populations are often considered as intermediate stages of speciation. Bluegill sunfish (Lepomis macrochirus) from Lake Waban, Wellesley, MA have diverged into two ecomorphs based on their diet, occupied habitat and morphology. Littoral bluegills are generalist feeders that consume a variety of aquatic invertebrates. Pelagic bluegills feed primarily on Daphnia. We aimed to understand if suction pressure generation, prey capture behaviors and pharyngeal jaw morphology differed between the littoral and pelagic ecomorphs feeding on three prey types. Littoral and pelagic bluegills showed similar feeding kinematics and peak pressure, however, significant differences were observed among prey types within an ecomorph. Feeding events on brine shrimp were slower and accompanied by less negative pressure for both ecomorphs. Littoral bluegills varied their use of ram among prey types, however, pelagic bluegills (zooplankton specialists) did not. Similar to previous studies, when presented with different prey items both dietary generalists and specialists varied equally in most aspects of their feeding behaviors. However, pelagic bluegills (dietary specialists) did not vary in their approach behaviors. Despite the lack of differences in trophic morphology among the individuals sampled here, the prey approach behaviors of dietary specialists appears to be fixed in pelagic bluegills. This result deemphasizes the importance of suction during feeding and places more importance on prey approach behaviors.