GENETIC AND PHYSIOLOGICAL ADAPTATION OF THE COPEPOD EURYTEMORA AFFINIS TO SEASONAL TEMPERATURES

Evidence of significant additive genetic (genic) variance in temperature tolerance of the copepod Eurytemora affinis was derived from several sources. Differences were observed between average tolerances of progeny of animals exposed and not exposed to heat shock in a power plant. Genic variance was estimated using offspring-parent regressions, full-sib, and half-sib covariances, with quite consistent results. Expressed genic variance between male progeny was always higher than that among female progeny.—The pairs of estimates obtained were as follows: female heritabilities first, 0.40 ± 0.09 and 0.84 ± 0.35 (half-sibs); 0.20 ± 0.09 and 0.79 ± 0.24 (full-sibs); 0.11 ± 0.10 and 0.89 ± 0.45 (full-sibs); 0.28 ± 0.18 and 0.78 ± 0.29 (full-sibs); 0.11 ± 0.44 and 0.72 ± 0.26 (offspring-parent regression). There was no evidence of either nonadditive genetic variance or common environmental (maternal and brood) effects, implying that the genetic variance was mostly additive and was not maintained because of heterozygous advantage.—The presence of so much genetic variance is surprising in view of the high physiological adaptation found earlier, especially in females.