Temperature, kairomones, and phenotypic plasticity in the rotifer Keratella tropica (Apstein, 1907)

Abstract

A Patagonian strain of Keratella tropica exhibits extensive non-genetic variation in spine development and body size. This study experimentally investigates the effect of temperature (10, 15, 20, and 25°C), both alone and with Daphnia and Asplanchna kairomones, on spine and lorica length. Temperature by itself had a major effect on right and left posterior spines and the lorica; these increased in length as temperature decreased, most notably from 20 to 15°C. At these two temperatures and a high food level (1 × 104 cells Cryptomonas erosa ml−1), lengths were, respectively, ca. 24 and 38 μm for the right posterior spine, 19 and 32 μm for the left posterior spine, and 116 and 126 μm for the lorica. A lower food concentration (2 × 103 cells C. erosa ml−1) at these two temperatures had little effect; the left posterior spine and lorica were slightly but significantly smaller. The growth-promoting effects of low temperature and kairomones generally were additive. Daphnia induced a moderate increase in the length of both posterior spines and lorica; these increases were significantly greater at 15 than 20°C. Asplanchna induced a great elongation of the right posterior spine, a reduction or loss of the left posterior spine, and moderate elongation of the outer two pairs of anterior spines. The right posterior spine and anterior spines were of similar length at 15 and 20°C, but the left spine and lorica were significantly longer at 15°C. Temperature and kairomones from Asplanchna and some crustaceans control the expression of a great variety of phenotypes and probably are largely responsible for seasonal changes in the spine development of this rotifer in natural communities.