Predator-specific reversibility of morphological defenses in Daphnia barbata

Inducible defenses are a common phenotypically plastic response to a heterogeneous predation risk. Once induced, these defenses cannot only lose their benefit, but even become costly, should the predator disappear. Consequently, some organisms have developed the ability to reverse their defensive traits. However, despite extensive research on inducible defenses, reports on reversibility are rare and mostly concentrate on defensive behavior. In our study, we investigated the reversibility of morphological defenses in the freshwater crustacean Daphnia barbata. This species responds to Notonecta glauca and Triops cancriformis with two distinctively defended morphotypes. Within the numerous defensive traits, we found both trait-and predator-specific reversibility. Body torsion and tail-spine-related traits were highly reversible, whereas helmet-related traits remained stable, suggesting different physiological constraints. However, in general, we found the defenses against Triops mostly reversible, while Notonecta-induced defenses were persistent and grew further, even in the absence of a predator.