Intraspecific variability in the thermal dependence of locomotion, population growth, and mating in the ciliated protist Euplotes vannus

Adaptation to the thermal environment depends upon heritable, intraspecific variability in the thermal dependence of organismal function. Variability in the thermal dependence of crawling speed, population growth rate, and mating compatibility among four strains of the ciliate Euplotes vannus (LL1, Elba, Por7, and Sard6) was tested for. The thermal dependence of crawling speed and population growth rate differed significantly among the four strains. One strain (LL1) showed evidence of positive thermal compensation, whereas other strains showed mixed or no acclimatory responses. The frequency of conjugation between strains of E. vannus was also temperature-dependent. This finding in particular has important implications for Euplotes systematics. Differences in functional traits among these clonal strains represent genotypic variability that may broaden the range of thermal environments available to E. vannus and may, in conjunction with differential mating, accelerate the evolutionary response to selection. Such variability may be particularly advantageous for E. vannus, an organism common to shallow marine environments (eg, tidal pools) that undergo substantial daily and seasonal changes in temperature. -from Authors