GENETIC AND PHYSIOLOGICAL FLEXIBILITY 461 



effective range of temperatures over which reproduction occurs in an 

 individual copepod, 20 ovigerous females and 10 males collected at 

 0°C were placed in each of ten flasks, at 4°C, and the resulting 

 progeny were allowed to mature at temperatures increasing to 27 and 

 29°C (five flasks at each temperature). At 27°C, three of the five 

 flasks had survivors, but only one flask contained ovigerous females. 

 At 29°C, four of the five flasks had survivors, but only one ovigerous 

 female was seen. No progeny were obtained at either 27 or 29° C. 

 The outer limit of tolerance of animals collected at 0°C and grown in 

 a slowly increasing temperature seems to be below 30°C, at least in 

 the laboratory. 



In the second experiment, a test of whether females and males 

 collected at 0°C would reproduce at the other end of the 

 temperature range, six of ten females in one flask produced egg sacs 

 at 27°C. In the other flask, however, all animals except one male 

 died. At 28 and 29°C, all animals were dead at 3 days except one 

 female in each flask. These experiments indicate that the reproduc- 

 tive range of one phenotype is less than the total range of 

 environmental temperatures. Information is needed on the rela- 

 tionship between temperature tolerance and reproductive capacity to 

 determine if adaptation to thermal stress may actually be influencing 

 the reproductive capacity of the species. 



DISCUSSIOIM 



The method used to measure temperature tolerance in individuals 

 was not conventional. Some of the existing assays of temperature 

 tolerance were unsuitable because data on individuals could not be 

 obtained. These assays included time to death of 50% of the 

 individuals (Mattice and Dye, 1976), temperature causing 50% 

 mortality after 24-, 48-, or 96-hr intervals (many investigators), and 

 proportion surviving after constant time at high temperature 

 (Carlson, 1974). I tried using the temperature at which activity 

 ceased as a criterion, in a manner similar to the widely used critical 

 thermal maximum (CTM) assay (Gonzalez, 1974; Wallis, 1975; 

 Hassan and Spotila, 1976; McFarlane, Moore, and Williams, 1976; 

 Murphy et al., 1976). Although Gonzalez used CTM successfully 

 with copepods, I found very little variation in the temperature at 

 which they became inactive; it was almost always around 35 C. 

 Furthermore, I needed to be sure they survived the assay, at least in 

 the genetics experiments in which they were to be bred. 



The time to enter a coma after a temperature shock, the assay I 

 used to measure temperature tolerance, proved to be repeatable and, 



