The ZoMBiE Lab: Can we use the brain to unlock behavior?

Although they sometimes have a reputation for being pre-programmed, “eating machines”, elasmobranchs (sharks, skates, and rays) are capable of a wide range of complex behaviors and have relative brain sizes that are comparable to birds and mammals. Our lab (The ZoMBiE Lab) at the University of North Carolina Wilmington is working to characterise variation in the brain to better understand sensory specialisation and even “intelligence” in these species.

What can the brain tell us?

It turns out, features such as the size of the brain, relative to body size, and the relative size of major brain components can vary considerably between species. For example, the brain of a deep-sea dogfish, inhabiting deep, dark waters, has enlarged brain regions that process olfactory, electroreceptive, and lateral line cues—which suggests a specialisation of non-visual senses. On the other hand, the brain of a reef shark, occupying the well-lit, spatially complex reef habitats, shows expansion of regions responsible for spatial learning, memory, and visual processing. We have examined the brains of nearly 200 species and found that differences in brain traits correlate with ecology and life history across these fascinating species. This suggests that we can make predictions about the relative importance of different sensory systems just by looking at the brain.

Brains from seven species of elasmobranchs to illustrate brain diversity. Top row: the great hammerhead (Sphyrna mokarran). Bottom row, left to right: lemon shark (Negaprion brevirostris), brownbanded bamboo shark (Chiloscyllium punctatum), spiny dogfish (Squalus acanthias), argus skate (Dipturus polyommata), cowtail stingray (Pastinachus atrus), narrownose chimaera (Harriotta raleighana). Figure adapted from Yopak (2022)

But does the brain of a juvenile match an adult?

The story gets more intriguing still: we have uncovered that the brain doesn’t just vary between species – it can actually change throughout life in the same species. A really unique feature of an elasmobranch brain is that it can grow forever — unlike our brains — fishes experience brain growth through adulthood. This feature allows us to ask some fascinating questions about whether certain brain regions expand as these animals move between habitats. In the species we’ve studied so far, we’ve found that the brain grows throughout life, but that the relative size of its regions shifts. For example, in the Atlantic sharpnose shark, Rhizoprionodon terraenovae, as the animals grew, we found a significant increase in the relative size of brain regions responsible for odour detection and motor control, but a significant decrease in the brain regions responsible for vision. This suggests that the brain can unlock a window into the ecology of these species and provide information about how sensory reliance may shift throughout life.

How can we apply this to sawfish conservation?

While our understanding of brain variation is improving, there is a distinct lack of these kinds of data in more rare and endangered species. Sawfishes (Pristidae) are a family of highly-modified rays, characterised by a saw-shaped rostrum. Due to severe range restriction and population decline in the last century, the smalltooth sawfish, Pristis pectinata, was added to the US endangered species list on April 1, 2003, and is currently found primarily in southwest Florida. Working with close collaborator Dr. Gregg Poulakis at the Florida Fish and Wildlife Conservation Commission (FWC), we have been sampling tissue from opportunistic mortalities of smalltooth sawfish for the last decade. Our first goal is to characterise the brain of the smalltooth sawfish across different size classes to predict behavioural and sensory shifts, which will contribute to our understanding of smalltooth sawfish ecology and may contribute to aspects of long-term recovery planning. Data from healthy individuals serves as a baseline atlas of normal brain growth, from which to understand neural anomalies in the future.

A project such as this requires collaboration across a massive team of amazing researchers. In addition to support from SOSF, this work is bringing together FWC, the Fish and Wildlife Foundation of Florida, Havenworth Coastal Conservation, and the Bonefish Tarpon Trust.

Want to read more about some of our lab’s work we discussed above? Check out our publications page!

Reference:

*Yopak KE. 2022. Advances in Chondrichthyan Neurobiology. In Biology of Sharks and Their Relatives, Edition 3. New York: CRC Press. pp 105-142 ISBN 9780367861179