Predator-specific reversibility of morphological defenses inDaphnia barbata

Abstract

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.

Predator‐specific inducible morphological defenses of a water flea against two freshwater predators

“…Furthermore, the formation of specialized defensive structures has been described, for example, the expression of neckteeth in D. pulex as a response to Chaoborus larvae (Krueger & Dodson, 1981), or the large crest in species of the D. carinata complex induced by backswimmers ( Anisops sp., Notonectidae; Grant & Bayly, 1981). Although inducible defenses in Daphnia have been intensively studied throughout the last decades, so far unrecognized defenses as well as novel defense mechanisms and adaptions are still revealed on a regular basis (Herzog & Laforsch, 2013; Herzog, Rabus, Wolfschoon Ribeiro, & Laforsch, 2016; Herzog, Tittgen, & Laforsch, 2016; Maurone, Suppa, & Rossi, 2018). Many of these recently discovered defenses have been found in Daphnia inhabiting pools and temporary ponds.…”

“…For instance, D. magna exposed to T. cancriformis , expresses an increased bulkiness, that is, a larger and wider body, an elongated tail spine and a fortified exoskeleton (Rabus & Laforsch, 2011; Rabus, Söllradl, Clausen‐Schaumann, & Laforsch, 2013; Rabus, Waterkeyn, Van Pottelbergh, Brendonck, & Laforsch, 2012; Riessen et al, 2012). Daphnia barbata not only responds to predatory invertebrates in general but in fact modulates its defensive traits, specifically adapted against the different hunting strategies of T. cancriformis or the backswimmer N. glauca (Herzog & Laforsch, 2013; Herzog, Rabus, et al, 2016; Herzog, Tittgen, & Laforsch, 2016).…”

Predator‐specific responses of Moina macrocopa to kaironmones from different fishes

“…Natural selection produces a finely tuned array of defenses in organisms that keep them relatively safe when coping with predator stress. In contrast to inherent defenses, inducible defenses allow organisms to reap benefits while saving potential costs associated with investment in the defensive strategy when it is not needed (Agrawal, Laforsch, & Tollrian, ; Herzog, Tittgen, & Laforsch, ).…”

Induction and reversibility of Ceriodaphnia cornuta horns under varied intensity of predation risk and their defensive effectiveness against Chaoborus larvae

“…When predation risks disappear, the prey organism may reverse the phenotype to increase its fitness (Gabriel et al., 2005). Some reversible processes can happen in ontogeny (Herzog et al., 2016), whereas some require multiple generations (Albini et al., 2019; Walsh et al., 2015). Thus, understanding the induction and reversibility of inducible traits in an environment with fluctuating predation pressure remains challenging.…”