Temperature Coefficients for Development in Cladocerans.

Abstract

In an earlier paper 1 it was shown that the temperature characteristics for the duration of an adult instar in several species of cladocerans were of the same order of magnitude as those found for development in other arthropods, but that certain specific differences were still markedly manifest. The temperature characteristics for the different temperature ranges and also the position of the critical temperatures or “breaks” in the log rate against reciprocal absolute temperature graphs were accorded a natural interpretation in terms of the geographical distribution and seasonal rhythms of the species studied. The present paper presents data on the temperature coefficients for the complete parthenogenetic generation cycle of several common species of cladocerans.

The literature on the biological application of van't Hoff's rule has been summarized by Kanitz 2 and Przibram. 3 Most of the papers dealing with this subject have been concerned with the relative magnitudes of the temperature coefficients and a subsequent classifying of vital activities into those controlled by physical forces and those controlled by purely chemical reactions. The comparison of several species of cladocerans reared in the laboratory for many generations under similar environmental conditions should reveal specific differences, should such be present, and might be taken to suggest a means for the physiological comparison of related forms. In addition to the ease of propagation in the laboratory, cladocerans are well adapted for such a study as their parthogenetic reproduction insures material that is genetically uniform, and their development by instars provides stages which are morphologically well defined.