Thermal Tolerance of Dragonfly Nymphs. II. Comparison of Nymphs from Control and Thermally Altered Environments

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Abstract
Dragonfly nymphs were collected from ponds and streams thermally altered by reactor cooling water and from control ponds and streams. The critical thermal maxima of seven species of dragonfly nymphs were estimated at acclimation temperatures of 12, 16, 20, 24, 28, and 32 C. Within each environment, species with greater mean body length exhibited a higher thermal tolerance than smaller species. Species differences in critical thermal maximum (CTM) were statistically significant within each environment examined, but these differences were trivial relative to the much greater influence of acclimation temperature. Mean CTM was significantly regressed against acclimation temperature in each species. Nymphs from a thermally elevated pond exhibited a greater increase in CTM per degree rise in acclimation temperature than nymphs from other habitats. Mean thermal tolerances of dragonfly nymphs from the four environments increased in the following order: control stream, control pond, thermal stream, and thermal pond.

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