Evolution of novel jaw joints promote trophic diversity in coral reef fishes

Abstract

We investigated the functional morphology and ecology of biting among the squamipinnes, an assemblage of nine successful and distinctive reef fish families. We demonstrate that an intramandibular joint (IMJ) may have evolved at least three and possibly five times in this assemblage and discuss the impact of this recurring innovation in facilitating prey-capture by biting. Using character mapping on a supertree for the squamipinnes, we reveal up to seven gains or losses of intramandibular flexion, all associated with trophic transitions between free-living and attached prey utilization. IMJs are basal in six of the studied families whereas the origin of intramandibular flexion in the Chaetodontidae (butterflyfishes) coincides with a transition from ram-suction feeding to benthic coral feeding, with flexion magnitude reaching its peak (49 ± 2.7°) in the coral scraping subgenus Citharoedus. Although IMJs generally function to augment vertical gape expansion during biting behaviours to remove small invertebrates, algae or coral from the reef, the functional ecology of IMJs in the Pomacanthidae (angelfishes) stands in contrast. Pomacanthid IMJs exhibit over 35°of flexion, permitting gape closure when the jaws are fully protruded. We demonstrate the widespread IMJ occurrence among extant biters to result from a complex convergent evolutionary history, indicating that the IMJ is a major functional innovation that enhances biting strategies in several prominent reef fish groups.

Mechanics of snout expansion in suction feeding seahorses: musculoskeletal force transmission

“…Note, however, that the orientation of the hinge axes of the ceratohyal and dentary symphysis differ considerably in H. reidi (Fig.2). Although articulations between dentaries and anguloarticulars (Aerts et al, 1987;Vial and Ojeda, 1992;Konow et al, 2008;Ferry-Graham and Konow, 2010), and between the anterior and posterior ceratohyals of a single side (Diogo, 2005; are relatively common in actinopterygian fishes, the model assumes that mobility in these connections is negligible in H. reidi. The posterior ceratohyal bone tapers ventrally where there is a strongly interdigitated, firm synchondrosis with the anterior ceratohyal bone (Leysen et al, 2011).…”

Feeding characteristics reveal functional distinctions among browsing herbivorous fishes on coral reefs

“…These refined groupings are based on studies considering both behaviour (e.g., microhabitat utilization of biting) and morphology, especially jaw-shape, dentition, jaw articulation, and musculature (Bellwood and Choat 1990;Ceccarelli et al 2005;Konow et al 2008;Bellwood et al 2014). While all of these grazing fishes may facilitate the removal of algae from turfs, they have different dietary targets and means of ingestion.…”

The cerato-mandibular ligament: a key functional trait for grazing in damselfishes (Pomacentridae)

“…Although different definitions of key innovations have been proposed [1][2][3][4][5][6][7], all of them share the basic idea that some attributes of the organism have been important over evolutionary time [8] and that the key innovation allows the utilization of resources in ways not previously possible [9,10]. The pharyngeal jaw in cichlids [11], the intramandibular joint in squamipinnes such as pomacanthids and acanthurids [12][13][14][15][16], the "beak-like" jaws in parrotfishes [17], the toepads of geckos [10,18], the presence of molars with a hypocone in mammals [19] are all classic examples of key innovations in vertebrates.…”