This adaptation was featured in a recent groundbreaking study on the striking Moorish Idol, Zanclus cornutus. This fish has the ability to move its jaws laterally, a remarkable evolutionary adaptation. Peter Wainwright, chair of the Department of Evolution and Ecology at the University of California, Davis, is the professor who spearheaded this finding. It uncovers a fascinating trait of an astonishing adaptive reef fish that is key to the process of herbivory on coral reefs.
Using high-speed video technology, Michalis Mihalitsis, now an assistant professor at the University of Guam, observed feeding behaviors in Zanclus cornutus. The research team substantiated their discovery with CT scans and dissections. Interestingly, they found that it’s not just the lower jaws of this fish species that can move sideways. The Moorish Idol’s special lateral jaw movement allows it to delicately pluck food off surfaces. It is uniquely able to position its mouth into cracks and crevices of the reef to reach algae hiding there.
Key Findings on Jaw Movement
The study published in the Proceedings of the National Academy of Sciences sheds light on how Zanclus cornutus utilizes its unique jaw movement. Wainwright noted the significance of this adaptation by stating, “They take a mouthful of algae and move their jaws to pull it off the surface.” This mechanism is key for their natural feeding behavior in the field. It is an example of how anatomical development responds and changes to fit new ecological niches.
In fact, 50% of all fish species on reefs eat primarily by grazing on algae and other organisms growing on the reef. The Moorish Idol’s unique alternative jaw motion sets it apart from a wide range of other fish species. Wainwright noted that even though this adaptation would not seem unusual from a human viewpoint, it is extremely unusual overall across vertebrates. He emphasized, “Being able to move your jaw from side to side might not seem surprising from a human point of view, but if you look across all vertebrate species—half of which are fish—it is almost unique.”
Implications for Reef Ecosystems
The study also looked into the feeding structures of other herbivorous fish like surgeonfish. These fish are typically lazy feeders, preferring to browse on algae growing on rocks and dead coral. The results demonstrate that Zanclus cornutus has the ability to move its jaw laterally. This unusual locomotion provides the fish with distinct benefits while foraging in jagged reef goby holes. Mihalitsis pointed out that “For Zanclus, this adaptation seems to relate to where they feed (reef cracks and crevices), whereas for the surgeonfish, how efficiently they feed.”
This difference in feeding adaptations further explains how different adaptations can similarly live together within reef ecosystems, increasing biodiversity and ecological harmony. Our work broadens the functional repertoire of vertebrates. It provides fascinating reversals into the evolutionary processes that drive species to adapt in such dramatic ways.
Broader Context of Herbivory on Reefs
The impact of this study goes well beyond the Moorish Idol. This is important because about half of all fish species on reefs are herbivores. Knowing how to best feed these super pollinators is key to more successful conservation efforts. As herbivores, these fish graze on algae, preventing it from overtaking coral and allowing healthy reefs to thrive. By limiting algal growth, they stop coral reefs from being suffocated by algae.
Wainwright expressed his surprise at the findings, stating, “I thought, holy cow, that’s not something we expected.” This groundbreaking find sheds new light on the anatomy of these creatures. Most importantly, it highlights how certain traits are fundamentally important across varied ecosystems.