THE ALLOCATION OF RESOURCES TO REPRODUCTION IN DAPHNIA-GALEATA - AGAINST THE ODDS

Variation in offspring size is a common phenomenon in many organisms. In cladoceran zooplankton large offspring are known to have a high sta rvation resistance. One could, therefore, expect offspring to be large at low food levels, whereas at higher food levels the production of m ore, but smaller, offspring would yield the highest parental fitness. However, in Daphnia galeata I found that individual offspring were sma llest at a low food level and largest at intermediate food levels. Mor eover, in contrast to the pre dictions made by several theoretical mod els, I found that large mothers produced larger offspring. The first d iscrepancy between data and theory could be explained by the existence of a maximum offspring size, combined with the difficulty of Daphnia to produce one egg less than was done in reality. The dependence of of fspring size on maternal size could be explained by the higher likelih ood of intraspecific competition when large (=old) females are present , and hence higher starvation risks for the offspring. It was found th at embryonic respiration was lowest at the lower food levels, and henc e the smaller individual egg size seemed to be compensated by lower ca rbon losses during development.