The majority of animal species undergoes a metamorphosis at some point during their life. It is thought that ontogenetic changes in diet served as a first step in the evolution of life cycles with metamorphosis. Because different resources require different morphologies, it is expected that species with an ontogenetic diet shift adapt their morphologies to the utilized resource. However, independent adaption to different resources may be prevented by genetic correlations between the different life stages. Therefore, increasing fitness in one stage can be disadvantageous for another stage, leading to a trade-off between juvenile and adult performance. Metamorphosis allows for decoupling of traits such that the different life-stages can evolve independently from each other under different selection regimes. Costs might be associated with metamorphosis as species often lose body mass during metamorphosis and are more vulnerable to predation. It is unknown under which ecological conditions the potential benefits of metamorphosis can outweigh the disadvantages. We used a size-structured biomass model with food–dependent growth and reproduction and the adaptive dynamics approach to study which ecological conditions favor the evolution of metamorphosis in species with an ontogenetic diet shift.
Results/Conclusions
In case of no metamorphosis, consumers fail to adapt to the adult resource when this negatively affects performance of small juveniles. Metamorphosis can break-up the correlation between the different life-stages such that adaptation to the adult resource becomes possible. However, metamorphosis only evolves when the productivity of the adult resource is very high. Surprisingly, a population with metamorphosis will keep this trait even when the adult resource productivity decreases, resulting in evolutionary hysteresis. Hence, metamorphosis is expected to evolve only when the benefits are very high, but can be maintained under less stringent conditions. Our findings contribute to a better understanding of why species with metamorphosis are so widespread.