Ecomorphology of the moray bite: relationship between dietary extremes and morphological diversity

Abstract

The pharyngeal jaws of moray eels function exclusively to transport prey from the oral jaws into the esophagus. This functional innovation in the moray pharyngeal jaw system occurred through the loss of some ancestral functions that presumably included prey processing. Therefore, the oral jaws of morays are used to capture and process prey. Dietary accounts suggest that morays can be categorized as either piscivorous or durophagous in feeding habits. These extreme feeding specializations that select for conflicting biomechanical demands on the oral jaws should result in two discrete clusters of cranial form and diet in morphospace. When functional characters underlying the oral jaws were examined for 10 muraenid species, piscivorous and durophagous morays occupied distinct areas of morphospace. Piscivores exhibited longer jaws, narrower heads, and long recurved teeth, while durophagous morays exhibited shorter jaws, greater dentary depths, and short blunt teeth. Durophagous morays process prey in their oral jaws, and their jaw-opening and jaw-closing ratios, along with their enlarged adductors, revealed jaws modified for force transmission. Pharyngeal jaw characters also separated moray species into different areas of morphospace. For example, Gymnomuraena zebra, a molluscivore, had more teeth on its pharyngobranchials than all other morays, and these teeth were long and thin compared with those of piscivores. The overall patterns of morphological variation corresponded well with moray dietary breadth. In addition, the range of jaw-opening and jaw-closing ratios revealed that for a clade of obligate carnivores, morays exhibit diverse biting behaviors.