Size Variation and the Distribution of Hemimetabolous Aquatic Insects: Two Thermal Equilibrium Hypotheses

Abstract

Adult body size and fecundity of a number of hemimetabolous aquatic insects depend largely on thermal conditions during the larval period. Small adults and reduced fecundity result when temperatures are either warmed or cooled with respect to more optimal thermal conditions. Temperature apparently affects adult size by altering the larval growth rate and the timing and rate of adult tissue development for each larva. The data suggest a new interpretation for the geographic distribution of aquatic insects.

Physiological Studies on Cancer irroratus Larvae. I. Effects of Temperature and Salinlty on Survival, Development Rate and Size

“…Growth rates at higher (24 'C) and lower (10 "C) temperatures were less than those for larvae cultured in temperatures between 15-18 "C. Similar growth patterns have been reported by Rothlisberg (1979) for the larvae of Pandalus jordani and by Sweeney and Vannote (1978) for several species of aquatic insects. Sweeney and Vannote suggest that the reduction in size in arthropods at the thermal extremes is expected due to a disequilibrium in the balance between growth rate and timing of ecdysis.…”

Body size shifts influence effects of increasing temperatures on ectotherm metabolism

“…Ameletus ludens and Ephemerella subvaria were 6% and 26% smaller, respectively, at a 3.1°C 304 warmer temperature (Sweeney & Vannote, 1978). None of the species in this study decreased 305 sufficiently in size for the indirect effect of temperature to offset the direct effect.…”

Implications of imaginal-size variation over the flight period in stoneflies (Plecoptera)

“…This explanation may also be valid in the case of stoneflies. Sweeney & Vannote (1978) and Vannote & Sweeney (1980) (in Moreira & Peckarsky 1994) interpret this decline in mean size as a phenomenological problem, based on the premise that temperature variations affect growth and development rates differently. Higher temperatures favour reproductive development while lower temperatures favour somatic development (growth).…”