Antipredator Behaviour of Caribbean Reef Squid (Sepioteuthis sepioidea)

Abstract

Predation is a major evolutionary driver of animal adaptation. However, understanding of anti-predator evolution is biased toward vertebrate taxa. Cephalopoda, a class in the invertebrate phylum Mollusca, is known for the diverse anti-predator strategies of its species, characterised by their behavioural flexibility. While ancestral cephalopods were protected by a hard outer shell, extant cephalopods have greatly reduced their reliance on physical defences. Instead, cephalopods have evolved highly developed senses to identify potential threats, cryptic skin patterns to avoid detection, startle responses to deter attack, and elaborate means of escape. The Caribbean reef squid (Sepioteuthis sepioidea, CRS) is one example of a species capable of complex and flexible skin patterning and a particularly diverse suite of anti-predator behaviours to defend themselves against regular predator encounters. CRS live in small shoals and previous observational research suggests that CRS coordinate their displays within a shoal to enhance the effectiveness of their displays. Here we present rare experimental field research on the anti-predator behaviour of CRS. Across two data chapters we examine the variety of displays used by CRS during trials employing model fish predators, selected to represent different levels of threat. We also begin to explore how and whether CRS coordinate these defences within a shoal. The results support suggestions from observational work in the literature that CRS appear to have ritualised display sequences which differ according to predator threat. Specifically, we found that behaviours such as paling and inking, which are indicative of high states of alarm, are reserved only for the most dangerous predators, with more moderate displays being used in lower threat encounters. We also found that certain displays are used at consistent points during the defensive sequence. Unravelling the complexities of cephalopod anti-predator behaviour and evolution remains challenging. However, recent technological developments available for cephalopod field and laboratory studies, coupled with new genomic data and analysis approaches, offer great scope to generate novel insights.