The epaulette shark walks both in and out of water and is found in the reef flats around the Great Barrier Reef in southern Australia.
A newly discovered walking shark that breaks all survival rules is the subject of a groundbreaking study by Florida Atlantic University and collaborators in Australia. Researchers studied how walking and swimming change in the epaulette shark (Hemiscyllium ocellatum) early development. This small, reef-dwelling benthic shark (about 3 feet) moves in and out of the water by wiggling its body and thrusting 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 deepen. isolate 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 between microhabitats under these harsh environmental conditions could directly impact its 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 they move) during the early stages of their lives.
As locomotor performance may be key to the robust response of epaulette sharks to harsh environmental conditions, FAU researchers in collaboration with Australia James Cook University and Macquaire University examined walking and swimming differences in neonatal (newly hatched) and juvenile walking sharks.
Newborns retain embryonic nutrition 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 hatchling sharks store begins to diminish as they mature into juveniles. As the yolk is depleted, the shark then begins to actively feed.
Due to the dissimilarities 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 moderate walking, brisk walking and swimming – using 13 anatomical landmarks along the fins, belts and midline of the body. They quantified axial body kinematics (velocity, amplitude and frequency of tail beat and body curvature) and axial body bending, fin rotation, duty cycle and tail kinematics.
Surprisingly, results published in the journal
Integrative & Comparative Biology
, showed that body shape differences did not alter the kinematics between newborn and juvenile walking sharks. Overall velocity, fin rotation, axial bending, 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 changes. These results 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 of juveniles.
“Studying epaulette shark locomotion allows us to understand the ability of this species – and possibly related species – to move in and out of the harsh conditions of their habitats,” said Marianne E. PorterPh.D., lead author and associate professor, Department of Biological Sciencesthe FAUs Charles E. Schmidt College of Science. “In general, these locomotor traits are critical to the survival of a small benthic mesopredator that moves through small reef crevices to avoid aerial and aquatic predators. These traits may also be linked to their sustained physiological performance under harsh environmental conditions, including those associated with climate change – an important topic for future study.
Investigating the link between locomotion and the physiological mechanisms needed to tolerate harsh environmental conditions represents an essential next step in understanding how this group of important mesopredators will respond to future ocean conditions.
“Studying how locomotor performance changes during early ontogenesis—perhaps the most vulnerable life stages, in terms of predator-prey interactions and environmental stressors—can offer insight into the kinematic mechanisms that allow animals to compensate for stresses to respond to locomotor and ecological stresses. requests,” Porter said.
Researchers studied how walking and swimming change in the early development of the epaulette shark. (Credit: Connor R. Gervais, Ph.D.)
The study’s co-authors are 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 University and Macquarie University, Sydney, Australia; and Jodie L.RummerPh.D., professor of marine biology in James Cook University’s College of Science and Engineering and research associate at the Arc Center of Excellence for Coral Reef Studies.
This work was supported, in part, by a National Science Foundation CAREER Award to Porter (IOS 1941713), and in part, by an Australian Research Council (ARC) Super Science Fellowship, ARC Early Career Discovery Award, and ARC Center of Excellence for Research Fellowship in Coral Reef Studies awarded to Rummer.