The walking shark learns to walk as a child

Aug. 19 () –

A newly discovered walking shark that break 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 changes in the early development of the epaulet shark (Hemiscyllium ocellatum). This small benthic shark (about one meter), which lives in the reefs, it walks both in and out of the water by moving its body and pushing with its paddle-shaped fins.

Found within reefs around South Australia’s Great Barrier Reef, epaulet sharks experience short periods of elevated CO2 and hypoxia (low oxygen), as well as fluctuating temperatures as reefs become isolated with the outgoing tide. Surprisingly, 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 epaulet shark’s ability 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 that have, only focus on stages of adult life. No study has specifically examined their locomotion during early life, until now.

Since locomotor performance may be key to epaulet sharks’ robust response to challenging environmental conditions, the FAU researchers, in collaboration with James Cook University and Macquarie University in Australia, 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 womb. In contrast, juveniles are slimmer because they actively seek out worms, crustaceans, and small fish. During development, the yolk stored by newborn sharks begins to decrease as they become juveniles.. As the yolk is depleted, the shark begins to actively forage.

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 hatchlings and juveniles during the three aquatic gaits they use (slow-to-medium walking, fast walking, and swimming). using 13 anatomical landmarks along the fins, girdles, and midline of the body. They quantified axial body kinematics (velocity, amplitude, and frequency of tail flapping, and body curvature) and axial body flexing, fin rotation, and duty factor and tail kinematics.

Surprisingly, the 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 speed, fin rotation, axial flexion, and tail-beat frequency and amplitude were consistent between early life stages.

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

“Studying epaulet 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,” he said. it’s a statement Marianne E. Porter, lead author and associate professor in the Department of Biological Sciences at FAU.

“Usually, these locomotor traits are key to the survival of a small benthic mesopreator that maneuvers in 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.”