ABSTRACT
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 present study 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°C. Experiments were carried out in 50 ml glass jars containing 25 ml synthetic medium with Chlorella vulgaris as food. The population growth rates (r) were derived. Analysis of variance (ANOVA) and post-hoc tests were used to quantify the intra-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°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°C. Of three morphotypes of L. ceratophylli, morphotype 3 had the highest r at 25°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.
ABSTRACT
We performed experiments using Aplysia neurons to identify the mechanism underlying the changes in the firing patterns in response to temperature changes. When the temperature was gradually increased from 11degrees C to 31degrees C the firing patterns changed sequentially from the silent state to beating, doublets, beating-chaos, bursting-chaos, square-wave bursting, and bursting-oscillation patterns. When the temperature was decreased over the same temperature range, these sequential changes in the firing patterns reappeared in reverse order. To simulate this entire range of spiking patterns we modified nonlinear differential equations that Chay and Lee made using temperature-dependent scaling factors. To refine the equations, we also analyzed the spike pattern changes in the presence of potassium channel blockers. Based on the solutions of these equations and potassium channel blocker experiments, we found that, as temperature increases, the maximum value of the potassium channel relaxation time constant, taun(t) increases, but the maximum value of the probabilities of openings for activation of the potassium channels, n(t) decreases. Accordingly, the voltage-dependent potassium current is likely to play a leading role in the temperature-dependent changes in the firing patterns in Aplysia neurons.