Adaptations of calanoid copepods for escaping predatory attacks

Abstract Calanoid copepods combine high-detection sensitivity, rapid reactions and powerful escapes to allow them to evade predatory attacks contributing to their success in pelagic marine environments. Four key evolutionary adaptations integrate behavioral, morphological and physiological features to enable this. The power output of their escape muscles is exceptionally high, propelling them to speeds that can outpace predators 10 times their size. This performance is associated with unusual muscle structure, suggesting an adaptation for both speed and power. Additionally, mechanosensory setae, crucial for detecting the subtle hydrodynamic signals of an attack, feature sensitivity-enhancing modifications to the arthropod design, including a dense array of microtubules in their neuronal dendrites. Further, giant axons speed the conduction of nerve impulses through the escape circuitry. Finally, around half of calanoid species possess myelin, a multilamellar axonal sheath that further boosts conduction speed. Thus, myelin can allow time for optimal escape, including re-orientation and enhanced temporal resolution of information reaching the central nervous system. Larval clownfish attacks on calanoids illustrate how these adaptations integrate to ensure successful evasion of predatory strikes. This review describes these morphological and physiological adaptations and explains how they contribute to the copepods’ remarkable escapes.