The walking shark learns to walk as a child

A newly discovered walking shark that breaks all the rules for survival is the focus of a study by Florida Atlantic University and collaborators in Australia.

They investigated how walking and swimming change in the early development of the epaulette shark (Hemiscyllium ocellatum). This small (about one meter) benthic reef-dwelling shark walks both in and out of the water by moving its body and pushing with its paddle-shaped fins.

Found within the reefs around the Great Barrier Reef of southern Australia, epaulette sharks experience short periods of elevated CO2 and hypoxia (low oxygen), as well as fluctuating temperatures as the reefs become isolated with the outgoing tide.

Remarkably, this walking shark is able to survive complete anoxia (without oxygen) for two hours without ill effects and at much higher temperatures than most other hypoxia-tolerant animals.

The ability of the epaulet shark to move efficiently between microhabitats in these challenging environmental conditions could directly affect its survival and physiological responses to climate change. However, very few studies have examined their kinematics (body movements). Those who have, only focus on stages of adult life. No study has specifically examined their locomotion during the early stages of life, until now.

Since locomotor performance may be key to epaulette sharks’ robust response to challenging environmental conditions, FAU researchers, in collaboration with Australia’s James Cook University and Macquaire University, examined differences in walking and swimming in newborn and juvenile walking sharks.

Newborns retain embryonic nutrition through an internalized yolk sac, resulting in a bulging belly. In contrast, juveniles are thinner because they actively search for worms, crustaceans, and small fish. During development, the yolk stored by newborn sharks begins to dwindle as they become juveniles. As the yolk is depleted, the shark begins to actively forage for food.

Due to the differences in body shapes, the 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 medium walking, fast walking, and swimming) using 13 anatomical landmarks along the flippers, girdles, and back. midline of the body. They quantified axial body kinematics (velocity, amplitude, and frequency of tail beat and body curvature) and axial body flex, flipper rotation, and work factor and tail kinematics.

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

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The data suggest that locomotor kinematics are maintained between neonate and juvenile epaulet sharks, even when their feeding strategy changes. These findings suggest that submerged locomotion in neonates is not affected by the yolk sac and the effects it has on body shape, as all aspects of submerged locomotion were comparable to those in juveniles.

“Studying epaulette shark locomotion allows us to understand the ability of this species, and perhaps related species, to move in and out of the challenging conditions of their habitats,” Marianne E. Porter, lead author and associate professor, said in a statement. in the FAU Department of Biological Sciences.

“In general, these locomotor traits are key to the survival of a small benthic mesopredator that maneuvers into small reef crevices to avoid aerial and aquatic predators. These traits may also be related to their sustained physiological performance under challenging environmental conditions, including those associated with climate change, an important topic for future study.” (YO)