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Temperature‐induced changes in the life cycle of Leuctra nigra (Plecoptera: Leuctridae) from a Lake District stream
Author(s) -
ELLIOTT J. M.
Publication year - 1987
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1987.tb01305.x
Subject(s) - instar , larva , zoology , growth rate , biology , ecology , growth model , mathematics , geometry , mathematical economics
1. The life cycle of Leuctra nigra (Olivier) took 2 years in a small stream in the English Lake District and the exponential growth of the larvae was scarcely affected by variations in water temperature (range 4.2‐14.0°C). Mean growth rates for three year‐classes were 0.43±0.01, 0.42±0.01, 0.39±0.05% body length day −1 . There were thirteen or fourteen larval instars for males and fourteen or fifteen for females. The ratio between successive instars was a constant 1.20 (conformed with Dyar's rule). 2. Larval growth and mortality were exponential at six constant temperatures (5.9, 8.2, 12.1, 15.8, 18.2, 19.8°C) in the laboratory. Mean growth rates (% body length day −1 ) increased directly with temperature from 0.37 (5.9°C) to 0.55 (19.8°C). Mean mortality rates (% day −1 ) increased directly with temperature from 0.20 (5.9°C) to 0.26 (12.1°C) and then markedly increased to 0.54‐0.58 at the three higher temperatures. Only 7‐10% of animals completed their life cycle at the three higher temperatures compared with 23–27% at the three lower temperatures. Egg production also decreased considerably at the higher temperatures. 3. As growth rates in the stream and laboratory were similar at similar temperatures (<14°C), the optimum conditions for growth in the laboratory were probably similar to those in the stream; therefore resources such as food and space were not restricting growth in the stream. 4. The implications of the temperature‐induced changes in growth and mortality are discussed and it is concluded that although the life cycle can change from semivoltine to univoltine with increasing temperature, the costs of a univoltine life cycle are high in terms of survival and egg production, both of which decreased markedly between 12.1 and 15.8°C. Therefore the optimum habitat for this species appears to be a summer cool stream (maximum temperature <14°C) and the optimal life cycle appears to be about 2 years from egg to adult.