Postembryonic growth in two species of freshwater Ostracoda (Crustacea) shows a size-age sigmoid model fit and temperature effects on development time, but no clear temperature-size rule (TSR) pattern

Although the temperature-size rule is a widespread phenomenon that describes the impact of temperature on the intraspecific size of ectotherms, what determines the wide intrinsic variation in moult increment and the intermoult period within and between Crustacea species remains unknown. This work characterizes the growth of freshwater ostracods Chlamydotheca incisa and Strandesia bicuspis under different controlled temperatures and identifies growth patterns. Animals were collected from temporary ponds in Argentina. The experiment was done at two constant temperatures: 17 and 23 °C. The intermoult time and the time from hatching to the final moult were calculated. Three different growth regression equations were tested: von Bertalanffy and two sigmoidal models (Sigmoid and Gompertz). For both species, significant differences in the duration of each instar were found by comparing individuals grown at 17 and at 23 °C. A strong temperature effect was noted on intermoult time but not on growth factors. The best model selected for the size-age relationship was a sigmoid growth type, indicating accelerated growth in the earliest juvenile instars. These results challenge the widely-accepted application of nonsigmoidal growth models and are in agreement with recent analyses of growth patterns in aquatic invertebrates when early juvenile instars are considered.