Effect of temperature on inter- and intraspecific isolates of Urotricha (Prostomatida, Ciliophora)

Ecological models often presume that all members of a functional guild, e.g. herbivorous ciliates, respond identically to temperature changes. To test this general assumption, we investigated if planktonic ciliates within the genus Urotricha exhibit distinct inter-and intraspecific responses to temperature. We examined the response of growth rate, cell volume, and production to changing temperature, using 6 temperatures between 5 and 30 degrees C. This experiment made 3 comparisons using: (1) different species isolated from the pelagic and littoral regions of the same lake; (2) different clones of the same species isolated from lakes of the similar trophic status, but different latitudes; and (3) different clones of the same species isolated from the pelagic region of a single lake. Using ANCOVA and ANOVA procedures (alpha = 0.05) to examine the data we demonstrated that: (1) ciliate species within a single genus may exhibit distinct responses to temperature, suggesting that treating ciliates as a single functional group is an oversimplification; (2) clones isolated from a laboratory culture of a single species, isolated from a single location, differ only to a small extent; and (3) clones isolated from different localities, but belonging to the same species differ considerably in their responses. Our data indicate that (1) temperature regimes may be an environmental niche that separates species and clones and (2) even where apparent morphological and molecular differences do not distinguish taxa, functional differences may still exist.