Bioenergetic and developmental response of a mayfly to thermal variation 1

Abstract

Egg development, growth, and emergence of Isonychia bicolor were observed in White Clay Creek (Pennsylvania) at ambient temperatures and in fluctuating experimental regimes with diel minima ranging from 12°–12.9°C and maxima between 12° and 20.1°C. Development rate of both eggs and nymphs was correlated positively with increased magnitude of the diel temperature pulse. Adult metamorphosis was most successful in regimes with diel maxima >16°C.Subimago body size and fecundity for winter generation females were about double those for the summer generation. Reducing spring and summer water temperatures lowered the fecundity of winter and summer subimagoes.Weight‐specific respiration rates of nymphs measured at 1.4 constant temperatures (range, 1°–21°C) increased with temperature but were inversely related to body size at a given temperature. Metabolic response to short term (1 h) changes in temperature was immediate; thermal acclimation or compensation was not observed.Energy budgets were calculated for male and female nymphs reared in various thermal regimes. Growth rates, net growth efficiencies, and production:respiration ratios of female nymphs were about twice those of males at all temperatures. Overall net growth efficiencies for I. bicolor averaged 44.16% and P:R ratios 0.84 for the combined sexes.