Thermal acclimation and tolerance to lethal high temperature in the mountain stream amphipod Paramelita nigroculus (Barnard)

Abstract

1. 1. Rates of upward and reverse acclimation were studied in Paramelita nigroculus (Barnard) from a mountain stream using a modification of the Critical Thermal Maximum (CTM) method. The upper lethal temperatures were measured using the LT 50 method. 2. 2. Acclimation rates were found to be typical of most crustaceans, with a gain of resistance to high temperature, following transfer from 8.5 to 20°C, being completed in 1–2 days. Loss of heat resistance took slightly longer (3 days). 3. 3. The species is strongly sexually dimorphic, males being significantly smaller than females. Neither sex, body length nor feeding status was found to affect tolerance levels. 4. 4. The LT 50 (min) for animals acclimated to 13.5°C ranged from approximately 300 min at 27°C to 4 min at 31°C. 5. 5. LT 50 values for 20°C-acclimated individuals were significantly higher than those acclimated at 13.5°C at corresponding test temperatures.