Strategic variation of egg size in Keratella cochlearis

The volume of a single amictic egg of Keratella cochlearis can vary between 32 000 and 132 000 mu m(3). Much of this variation is related to the size of the female laying the egg. When compared to populations in Europe, those in the Southern Hemisphere (Southern Africa and New Zealand) show a smaller increase in egg volume per unit increase in lorica length. Both lorica length and egg volume show a strong negative correlation with temperature. At high temperatures the females are smaller and they lay smaller eggs, but there are differences between populations in different lakes. In oligotrophic and high altitude lakes there is less variation than in lowland eutrophic lakes.