GENETIC AND PHYSIOLOGICAL FLEXIBILITY 



457 



TABLE 1 



ESTIMATES OF HERIT ABILITY* (±SE) AND GENETIC 

 VARIANCE IN TEMPERATURE TOLERANCE OBTAINED FROM 



FOUR EXPERIMENTS 



*Heritability estimates from full-sibs are biased upward (see Appendix A and 

 discussion in text). Standard error of heritability was calculated according to 

 Falconer (1963). 



reproduction observed. Ten pairs of males and females in each of two 

 flasks were placed at each temperature for 3 days, and any ovigerous 

 females were noted. 



RESULTS 



Table 1 summarizes data presented more extensively elsewhere 

 (Bradley, 1978b). Several conclusions can be drawn. First, 

 Eurytemora populations vary considerably in genetic influence on 

 temperature tolerance. Second, the genes express themselves more 

 clearly in males than in females, perhaps because the greater 

 physiological variances in females may tend to obscure genetic 

 differences. Third, on the basis of the similarity of estimates of 

 heritability from full-sib covariances, on the one hand, and half-sib 

 covariances and offspring— parent regressions, on the other, most of 

 the genetic variance seems to be additive (see Appendix A). We 

 should note that the lower heritabilities in female progeny are not 

 the result of higher phenotypic variances; the genetic variances are 

 also lower. 



There were two other sources of evidence for genetic variance in 

 temperature tolerance: (1) Significant and persistent differences in 

 tolerance were found between two separate populations of 



