Behavioural versatility of the giant murex Muricanthus fulvescens (Sowerby, 1834) (Gastropoda: Muricidae) in interactions with difficult prey

Abstract

Muricanthus fulvescens, one of the largest muricid gastropods in the world, was once thought to be a behavioural specialist, using its shell to grind feeding holes in bivalve prey. New experimental observations, however, reveal that this predator employs up to four modes of predation, including selective use of shell grinding and edge drilling in interactions with the large, thick-shelled venerid clam Mercenaria campechiensis. Shell-grinding attacks were found to be slightly faster than edge-drilling attacks, but had a lower success rate. Choice of predatory mode was more strongly correlated with the prey's anterior-posterior shell length than predator size. Smaller clams were attacked more frequently by shell grinding, while larger, thicker prey tended to be attacked by edge drilling. Several larger predators edge-drilled their prey successfully after first failing with the faster grinding behaviour; trial-and-error initiation of attacks with the more rapid grinding behaviour, however, was rare and expressed only by the largest predators. We also report an anecdotal observation of wall drilling and morphological evidence consistent with two modes of edge-drilling attacks, including drilling of larger holes for proboscis insertion and feeding and smaller, barely detectable (<1 mm) holes for toxin injection. Toxin use is further supported by a lack of correlation between predator size and inner drill-hole dimensions. The occurrence of previously undetected diversity in predatory modes of M. fulvescens, a common, easily accessible species, demonstrates how much we have to learn about ecological versatility in muricids and its role in muricid evolution.