Microdefences in Daphnia - Predator induced changes in spinule morphology and distribution

Patricia Diel1, Christian Laforsch1, Max Rabus1
1 Animal Ecology I, University of Bayreuth

P 4.9 in BayCEERversity: Across scales, compartments & communities

Phenotypic plasticity in defensive traits is a common response of prey organisms in ecosystems with variable predation regimes. Cladocerans of the genus Daphnia are known for their ability to express a large variety of inducible morphological defences in response to invertebrate predators, thereafter rendering the daphnids less susceptible to predation. So far, primarily large-scale morphological defences, like helmets, crests and tail-spines have been documented. However, less visually prominent traits may contribute to the effectiveness of the defence. Here, we studied the expression of predator-induced micro defences, namely changes in the morphology of the spinules, tiny spines located on the ventral margins of the carapace and the dorsal ridge, and the size of the spinule bearing areas (SBAs), in Daphnia magna and D. longicephala. The results show that both D. magna and D. longicephala expressed micro defences, against the invertebrate predators Triops cancriformis and Notonecta glauca, respectively. Thereby, the induced individuals showed significantly longer spinules along the ventral margins and the dorsal ridge, in comparison to non-induced individuals. In addition to the size of the spinules, also predator-induced changes in their spatial distribution could be observed: In D. magna, Triops induced the expression of a significantly larger dorsal SBA, while Notonecta-induced D. longicephala showed a significantly larger ventral and a smaller dorsal SBA. Since these micro defences likely interfere with the fine cuticular appendages of the feeding apparatus of predatory invertebrates, we anticipate that these minute defensive structures may act synergistically with the macro defences and thus enhance the effectiveness of the defence.

Keywords: Daphnia, phenotypic plasticity, predator prey interactions, inducible defences