Experimental investigation of physiological factors that may influence microhabitat specificity exhibited by Leptorhynchoides thecatus (Acanthocephala) in green sunfish (Lepomis cyanellus)

Representatives of Leptorhynchoides thecatus (Acanthocephala) inhabit ceca of green sunfish but cannot survive in the anterior intestine. The influenc e of elevated cecal protein concentrations, pH, and amounts of lumenal mate rials on the microhabitat specificity of L. thecatus was investigated. An a ttempt was made to alter the distribution of worms in starved fish, in fish of which cecal pH was reduced, and in fish of which intestinal protein con centration was elevated. Protein concentration and pH showed no effect on w orm distribution. Starving hosts had no effect on worm number or distributi on but resulted in retardation of worm growth and development, providing a mechanism by which worms may overwinter and by which peak egg production ma y coincide with abundance of the amphipod intermediate host. None of the fa ctors investigated is solely responsible for the microhabitat specificity o f L. thecatus. It is suggested that helminth site specificity is characteri zed by long histories of adaptation to specific habitats with many physiolo gical adaptations being facilitated synergistically. Maximization of sexual congress may exert an important selective pressure favoring this establish ment of microhabitat specificity.