Morphological variation of the predatory cladoceran Leptodora kindtii in relation to prey characteristics.

The responses of invertebrate predators to changes in the morphology of their prey, and especially the responses for induced defences, are largely unexplored, compared with the vast amount of data on predator-induced defences. This study demonstrates that the size of the feeding basket, the anatomical structure used to capture prey by the predaceous freshwater cladoceran Leptodora kindtii, shows significant allometric changes with the average body size of the prey (herbivorous cladocerans) in six lakes of northeastern Poland. Prey density influences the basket size only in adult Leptodora individuals, whereas induced defences such as helmets of Daphniasp. seem to have no effect on Leptodora's morphology. In a feeding experiment it is shown that the increase in the feeding basket enables Leptodora to capture larger prey. The seasonal pattern of morphological change, and its measurable benefit suggest that the observed morphological variability of Leptodora is phenotypic plasticity.