Substrate Selection by Larvae of the Sessile Rotifer Ptygura Beauchampi

Larvae of the sessile rotifer Ptygura beauchampi begin substrate selection activities when they chemotactually sense a stimulus associated with the glandular trichomes which cover their preferred substrate, the trap door region of the largest, prey capturing organs of the carnivorous aquatic plant, Utricularia vulgaris. Four other co—occurring congeneric species (U. gibba, U. inflata minor, U. intermedia, and U. purpurea) and 2 smaller, morphologically distinct, trap types of U. vulgaris were not colonized. All of these Utricularia traps (except U. purpurea) have glandular trichomes which are nearly indistinguishable from one another. The stimulus appears to be chemical in nature, arising from the terminal head cells of trichomes as they develop. The chemical stimulus (an allelochemic agent) may be the utricularian prey—lure first proposed by Cohn in 1875. This symbiotic relationship should be termed commensal because rotifers colonize, but do not feed on the plant or its prey, and because the plant is apparently not affected by the colonization.