Describe the forces of natural selection acting on the wild guppy population.
The strongest selection in most cases was not for size, but for age of maturity. Guppies under lower predation tended to mature later, and size was sometimes even negatively selected for. For example, guppies that have evolved under high predation pressure show early sexual maturation and increased reproductive effort (how much of their body weight is made of embryos). They also tend to have many embryos, but small ones. In addition, guppies also differ in their schooling and mating behaviors. Males from low-predation environments engage females in courtship and pursue them, displaying their coloration – males with more coloration tend to have higher reception from females. In contrast, in high-predation environments males tend to approach females quickly, because courtship behavior increases the chances of being spotted by a predator. Finally, when fish from a high-predation population are introduced to a previously guppy- and predator-free environment, they evolve to trait values similar to those of natural low-predation fish..