Evolution of complex life cycles

The majority of all animal species have a metamorphosis, even though fossil evidence suggests that this life-history strategy only evolved a few times. It is thought that ontogenetic niche shifts, where individuals change their diet, habitat, and/or behaviour during their life, have been the first steps towards complex life cycles where individuals undergo metamorphosis.
Niche shifts and metamorphosis are life-history strategies that evolved millions of years ago. Little is known about the ecological conditions that promoted their evolution. The aim of the research in this thesis is to understand under which ecological conditions niche shifts and metamorphosis may have evolved. The evolution of these life-history strategies is investigated with mathematical models that study evolution in an ecological setting.
The results in chapter 2 and 3 show that the evolution of ontogenetic niche shifts is limited by a trade-off between early and late foraging efficiencies. While it is beneficial for individuals to switch to another food source during their development, it is not possible to specialize on this food when this has negative consequences for their offspring. In chapter 4 it is shown that metamorphosis evolves to allow independent evolution of the different life stages. Metamorphosis is, however, very costly and can therefore only evolve under limited conditions. The results in chapter 5 show that metamorphosis does often not disappear when the ecological conditions change. The main result of this thesis is that metamorphosis is difficult to evolve, but, once evolved, it is a robust strategy that does not easily disappear.