| Genetic correlations between high temperature tolerance and several traits either related to fitness or influenced by temperature were studied in a Chesapeake Bay population of the copepod Eurytemora affinis (Poppe). Broods from two samples of wild ovigerous females were isolated and reared under controlled laboratory conditions. Mature progeny were measured for elevated temperature tolerance, low dissolved oxygen tolerance, length, width, first brood size and first brood viability.; Progeny from the two samples represented, genetically, their respective parents from two distinct generations, who were exposed to different selective pressures. March parents developed during a period of decreasing temperature (5(DEGREES) to 0(DEGREES)C) followed by increasing temperature (0(DEGREES) to 5(DEGREES)C). May parents, in contrast, developed during a period of increasing temperature (approximately 5(DEGREES) to 18(DEGREES)C).; Phenotypic differences in the progeny were detected between samples within each sex. Progeny means for both sexes differed between samples for temperature tolerance, length and width. Female progeny means also differed between samples for brood size and brood viability. Phenotypic differences in low dissolved oxygen tolerance were absent in both sexes.; All within sex, within sample, full-sib estimates of heritability were significantly greater than zero. Heritabilities were consistent between samples for males, but not for females. Heritabilities decreased for both tolerance traits and increased for both measures of brood size in females from March to May. Dominance variance may have inflated the heritability estimates.; Genetic correlations were estimated for each sex within each sample using family means. Statistically significant correlations were evident in females, but not in males. The genetic correlation between the two tolerances changed from negative to positive between March and May. In contrast, the correlations between temperature tolerance and both measures of brood size changed sign in the opposite direction.; Temporal variation for temperature in situ produced a phenotypic, but not a genetic, response when measured in male progeny. In female progeny, both responses were observed and suggest genetic trade-offs between brood size and temperature tolerance.; The observed changes among first-filial phenotypic means, heritabilities and genetic correlations may have been caused by either linkage disequilibrium or pleiotropy. In the absence of direct cytological evidence for E. affinis, it is suggested that linkage results from achiasmate females or chromosome ring structures during females gametogenesis, or from both. Areas for further research are suggested. |
