Thick cuticles as an anti-predator defence in nematodes

Abstract

Summary Although some anti-predator defences have been documented in nematodes, the role of the cuticle in defending against predator attacks remains unclear. Microscopical observations have suggested that certain Poikilolaimus species, including P. oxycercus and P. regenfussi, have thick cuticles relative to their congeners, which may represent an anti-predator defence, but the role of the cuticle in reducing predation has not been examined. To address this knowledge gap, we first quantified cuticle structure using transmission electron microscopy among four Poikilolaimus species (P. oxycercus, P. regenfussi, P. floridensis and P. carsiops). We then examined their survival rates following exposure to the predatory aphelenchoidid nematode, Seinura caverna, and assessed correlations between cuticle thickness and survival rate. The cuticles of P. oxycercus and P. regenfussi were significantly thicker than those of P. floridensis and P. carsiops. In addition, P. oxycercus and P. regenfussi had an osmophilic zone in their cuticle structure, which was not observed in P. floridensis and P. carsiops. Both thickness of specific cuticle zones and total cuticle thickness were positively correlated with survival in the presence of a predator, with the strongest correlation observed with the thickness of the osmophilic zone. We suggest that P. oxycercus and P. regenfussi have uniquely evolved cuticles among members of Poikilolaimus in terms of thickness and structure that play an important role in reducing predation.