Effect of Alternating Temperature on Embryonic Developmental Time of the Mayfly Cloeon triangulifer McDunnough
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The number of generations produced annually by the parthenogenetic mayfly Cloeon trianqulifer varies throughout its geographic range. It is hypothesized that in a polyvoltine species such as this one, the effect of a given temperature on the rate of development for an individual should remain constant regardless of life stage. To test this hypothesis, C. triangulifer eggs were maintained at a constant temperature (l4.7°C) except for 2 days exposure at a higher temperature (24.0oC). Exposure to the higher temperature occurred at different stages of embryonic development. Other eggs were kept constantly at 14.7 or 24.0o C as control treatments. Mean developmental time for the various treatments was compared to see if the stimulatory effects of the higher temperature had changed at some point in development. The length of the developmental period did not differ significantly among treatment groups exposed at different stages to both the high and low temperatures, indicating that the effect of a given temperature did not change during embryonic development. Possible causes of variation in developmental time are discussed.