Food size matters

By modifying their body shape, size, and reproduction,Daphniahas demonstrated adaptive resilience. However, whileDaphniais a model species for studyingphenotypic plasticity, the precise relationship between the prey's body size and their predator's size preference has not been established.

Now, a group including two universities in Kyoto has determined that prey size and risk of predation are strongly related to the medium-sizedDaphnia-- a small, planktonic crustacean -- targeted by aquatic insects and fish.

"This phenotypic plasticity has been shown to be expressed by a variety of factors, including predator type, predator mode, and density," says corresponding author Mariko Nagano of the Kyoto University of Advanced Science.

The two predator types ofDaphniaare typicallyChaoboruslarvae -- also known as phantom midge -- which prefer smaller prey, and fish, which prefer larger prey as they tend to hunt visually.

Collaborating in the study, Toyama Prefectural University and Kyung See University jointly conducted the team's meta-analysis of experiments on phenotypic plasticity. Results from the team's collective effort suggested that medium-sizedDaphniawould likely be the most vulnerable to predation among its genus by both predator types and therefore have the most defensive strategies.

The meta-analysis also suggests that the larval predators impose a greater influence onDaphnia's morphological change than do fish.

Overall, the small and medium-sizedDaphniaexpressed the highest degree of predator-induced plasticity, which the team found was more evident in smallDaphniathan would be expected from size-selective predation.

"The body size ofDaphniais a key trait influencing its plasticity expression and evolution," concludes co-author Hideyuki Doi of Kyoto University's Graduate School of Informatics.