GENETIC AND NON-GENETIC VARIABILITY IN TEMPERATURE TOLERANCE OF THE COPEPOD EURYTEMORA AFFINIS IN FIVE TEMPERATURE REGIMES

¹ Department of Biological Sciences, University of Maryland Baltimore County (UMBC), Baltimore, Maryland 21228

Genetic and nongenetic variation in temperature tolerance was measured in populations of copepods grown in two environments varying between 10° and 23°C on 26 day (SW) and 26 week (LW) cycles and in three constant environments at 10°C, 15°C, and 23°C.

Genetic variation was maintained and expressed in both sexes in the cycling environments, but declined in males in the 23°C constant environment, perhaps indicating constant directional selection.

Physiological variation was similar in males and females, in contrast to earlier results, again suggesting an effect of selection. There was evidence of selection for physiological flexibility in males in the 23°C and 15°C environments.

A question arising was why sexual dimorphism in genetic variation and in physiological variation was maintained in nature but reduced, reversed, or even eliminated in the laboratory environment. Random drift was not a plausible explanation.