Why do Daphnia in temperate lakes develop pointed heads during late spring and summer?

In temperate lakes, some species of Daphnia exhibit a seasonal change in morphology, developing pointed heads during late spring and summer rather than the rounded heads seen in winter.1

This adaptation is primarily driven by the need to avoid predation by plankton-eating fish, whose feeding activity increases significantly during the warmer months. These fish tend to target larger, more conspicuous Daphnia. By developing a pointed and enlarged head, the Daphnia effectively reduces the size of its carapace and often its eye, resulting in an overall decrease in visibility to predators. While high water temperatures and turbulence are environmental factors that favor this development, the morphological shift serves as a critical survival strategy against increased predation pressure.1