Temperature-dependent demographic differences in sessile rotifers of the genus Limnias (Rotifera: Gnesiotrocha)

摘要

Aim : Rotifer research on sessile taxa has received less attention because they are not easy to identify in fixed samples. In the Lake Xochimilco, a Ramsar site in Mexico City, three morphotypes of L. ceratophylli and a single morphotype of L. cf. melicerta occur in different densities. The aim of this study was to test if temperature was responsible for the differences in the population densities of these morphotypes.Methodology : The presentstudy was carried out using population growth method consisting of 4 treatments (3 morphotypes of L. ceratophylli and one of L. cf. melicerta) at 20 and 25 degrees C. Experiments were carried out in 50 ml glass jars containing 25 ml synthetic medium with Chlorella vulgar's as food. The population growth rates (r) were derived. Analysis of variance (ANOVA) and post hoc tests were used to quantify the intro -and interspecific differences in the population growth rates.Results : The temperature levels for optimal population growth rates differed among the morphotypes of same species. At 20 degrees C, the morphotype 1 had the highest r (0.23 d(-1)) similar to that of L. cf. melicerta, while morphotype 3 had the lowest (0.15 d(-1)). For L. cf. melicerta, the r was higher at 25 C than at 20 degrees C. Of three morphotypes of L. ceratophylli, morphotype 3 had the highest rat 25 degrees C similar to that of L. cf. melicerta at same temperature.Interpretation : There were significant differences among growth patterns within the morphotypes of L. ceratophylli, depending on culture temperature. These trends highlight the relative importance of environmental variables in differentiating morphotypes of a sessile species complex which could explain their possible seasonal. changes in the natural waterbodies.