Time-limited environments affect the evolution of egg - body size allometry

Initial offspring size is a fundamental component of absolute growth rate, where large offspring will reach a given adult body size faster than smaller offspring. Yet, our knowledge regarding the co-evolution between offspring and adult size is limited. In time-constrained environments, organisms need to reproduce at a high rate and reach a reproductive size quickly. In order to rapidly attain a large adult body size, we hypothesize that, in seasonal habitats, large species are bound to having a large initial size, and consequently, the evolution of egg size will be tightly matched to that of body size, compared to less time-limited systems. We tested this hypothesis in killifishes, and found a significantly steeper allometric relationship between egg size and body size in annual, compared to non-annual species. We also found higher rates of evolution of egg and body size in annual compared to non-annual species. Our results suggest that time-constrained environments impose strong selec...