Researchers compare walking, swimming in newborns with bulging bellies and thin juvenile epaulette sharks

A newly discovered walking shark that breaks all the rules of survival is the subject of a groundbreaking study by Florida Atlantic College and collaborators in Australia. Researchers studied how walking and swimming change in the early development of the epaulette shark (Hemiscyllium ocellatum). This small, reef-dwelling benthic shark (approximately 3 feet) enters and forms water by wiggling its body and pushing with its paddle-like fins.

Found in the reef flats around the southern Great Barrier Reef in Australia, epaulette sharks experience short periods of high CO2 and hypoxia (low oxygen) as well as fluctuating temperatures as the reef flats become isolated with the ebb tide. Remarkably, this walking shark is able to survive complete anoxia (without oxygen) for two hours without adverse effects, and at a much higher temperature than most other hypoxia-tolerant animals.

The ability of the epaulette shark to move efficiently among microhabitats in these harsh environmental conditions could have an immediate effect on their survival and physiological responses to climate change. However, very few studies have looked at their kinematics (body movements). Those that have done so have only focused on the adult life stages. So far, no studies have specifically looked at their locomotion (how much they move) during the early stages of their lives.

As locomotor performance may be the key to the robust response of epaulette sharks to harsh environmental conditions, FAU researchers, in collaboration with Australia’s James Cook University and Macquaire University, examined gait and swimming differences in hatchlings (newly hatched ) and juvenile walking sharks.

Newborns retain embryonic diet via an internalized yolk sac, resulting in a bulging belly. In contrast, juveniles are more slender as they actively feed on worms, crustaceans and small fish. During development, the yolk that newborn sharks store starts to diminish as they mature into juveniles. As the yolk is depleted, the shark then begins to actively feed.

Due to differences in body shapes, researchers expected to see differences in the locomotor performance of these walking sharks. To test their hypothesis, they examined the locomotor kinematics of neonates and juveniles during the three aquatic gaits they use – slow to moderate walking, brisk walking and swimming – using 13 anatomical landmarks along the fins, girdles and midline of the body. They quantified the axial body kinematics (velocity, amplitude and frequency of tail beat and body curvature) and the axial body bending, fin rotation, duty cycle and tail kinematics.

Surprisingly, results published in the journal Integrative & Comparative Biology showed that differences in body shape did not alter kinematics between newborn and juvenile walking sharks. Overall velocity, flipper rotation, axial flexion, and tail-beat frequency and amplitude were consistent across early life stages.

The data suggest that locomotor kinematics are maintained between neonate and juvenile epaulette sharks, even if their feeding strategy adjusts. These results suggest that submerged locomotion in neonates is not affected by the yolk sac and the effects it has on body shape, since all features of submerged locomotion were comparable to those of juveniles.

“Studying the locomotion of the epaulette shark allows us to understand the ability of this species – and possibly related species – to move inside and outside the harsh conditions of their habitats,” said Marianne E. Porter, Ph.D. lead author and associate professor. Department of Biological Sciences, Charles E. Schmidt School of Science at FAU. “In general, these locomotor qualities are essential for the survival of a small benthic mesopredator that moves through small reef crevices to avoid aerial and aquatic predators. These qualities may also be related to their general sustained physiological performance under harsh environmental conditions, including those associated with climate change – an essential topic for future studies.”

The Investigating the link between locomotion and the physiological mechanisms necessary to tolerate harsh environmental conditions represents an essential next step in understanding how this group of important mesopredators will respond to future oceanic situations.

“ Investigating how locomotor performance changes during early ontogeny—perhaps the most vulnerable life stages, in terms of predator-prey interactions and environmental stressors—may offer insight into the kinematic mechanisms that allow animals to compensate for stresses to respond to locomotor stresses. and ecological requirements,” Porter said.

Study co-authors Andrea V. Hernandez, an undergraduate student in the Department of Biological Sciences at FAU Connor R. Gervais, Ph.D. Research Fellow at the Arc Center of Excellence for Coral Reef Studies, James Cook dinner University and Macquarie College, Sydney, Australia and Jodie L. Rummer, Ph.D. Professor of Marine Biology at James Cook University College of Science and Engineering diner and Research Associate at the Arc Center of Excellence for Coral Reef Studies.

This work was supported, in part, by a National Science Basis Job Award at Porter (IOS 1941713), and in part, by an Australian Research Council (ARC) Super Science Fellowship, ARC Early Occupation Discovery Award and ARC Center of Excellence for Research Grant in Coral Reef Studies awarded to Rummer.

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