The relationship between temperature and duration of egg development in some epiphytic cladocera and copepoda from the River Thames, reading, with a discussion of temperature functions.

Data on the duration of egg development at 5, 10, 15 and 20°C are given for eight cladoceran and one cyclopoid copepod species found associated with the Yellow Water Lily (Nuphar lutea) in the River Thames. A decrease in temperature caused a marked increase in the time taken to complete development for all nine species. The data are compared with published data and a number of conclusions drawn. In general, cladoceran eggs tend to take longer to complete development than copepod eggs, and within the Cladocera the eggs of epiphytic species tend to take longer to develop than those of planktonic species, and the eggs of large species longer than the eggs of small species.The relationship of development time to temperature was examined, and the linear reciprocal relationship, Krogh's curve and the vant' Hoff-Arrhenius function were found to be inadequate. Statistical analysis of the data required a logarithmic transformation, and this gave a significantly curvilinear relationship for all nine species. A quadratic of the form: logD = log a + b log T + c(logT)2 gave the best fit for eight of the species, but this could be reduced to log D = log a ´+c ´ (logT)2 with only a slight decrease in the predictive value of the model. A comparison of regression lines showed that the data for each species could only be described properly by individual regression lines for each species: common slope or common intercept lines, or a single line were not valid. A survey of the literature suggests that the analyses in many previous investigations are statistically inadequate. A critical discussion of temperature functions is given.