EFFECTS OF BODY WEIGHT AND TEMPERATURE ON THE METABOLIC RATE OF HYALELLA CURVISPINA SHOEMAKER, 1942 (AMPHIPODA)

Hyalella curvispina Shoemaker, 1942 has a broad distribution across freshwater habitats of southern South America, where it can reach very high densities. This species plays an important role in food webs, linking a main portion of primary production with higher order consumers. In this work we provide the first data on the metabolic rate of H. curvispina and determine how it is affected by environmental temperature and individual body weight. Additionally, we present a predictive equation that allows the estimation of standard metabolic rate from temperature and body weight. The mean standard metabolic rate of juveniles of both sexes and adult males of H. curvispina was measured for a wide range of body weights (0.07 to 2.90 mg dry weight) at four temperatures (11.5, 18, 24, and 30 degrees C), covering the thermal range of its natural habitat. Metabolic rate showed an allometric scaling with body weight. Scaling exponents were significantly less than 1, having a mean value of 0.66 +/- 0.032. There was an interaction between body weight and temperature, thus scaling exponents varied with temperature, from 0.51 at 24 degrees C to 0.78 at 30 degrees C. An increase in temperature over the range 11.5-24 degrees C produced a raise in metabolic rate irrespective of body weight; between 24 and 30 degrees C, however, response to temperature varied with body weight. The metabolic rate of H. curvispina is similar to that in the two other species of Hyalella for which published data are available. Scaling of metabolic rate with body weight is similar to commonly reported results for other species, as well as to what is expected from theoretical considerations. The predictive equation presented in this work provides a means to estimate the standard metabolic rate of H. curvispina in further studies from temperature and body weight data.