In our Research Highlights blog series, we debut newly published fisheries research by our women of fisheries colleagues. If you have research you would like to highlight and share with our readers, submit a nomination form here!

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This Month’s Research Highlight:
Knaub J.L., M. Passerotti, L.J. Natanson, T. Meredith, and M. Porter. 2024. Vertebral morphology in the tail-whipping common thresher shark, Alopias vulpinus. Royal Society Open Science 11: 231473.

Thresher sharks, sometimes referred to as “whiptail” sharks, are easy to identify due to their characteristic tail resembling a scythe, a long-handled crop harvesting tool with a large, curved blade. There are three species of thresher shark in the world – bigeye (Alopias superciliosus), common (A. vulpinus), and pelagic (A. pelagicus) – which use their unique tails as weapons to “slap” their prey. As Jamie Knaub, a doctoral candidate and morphologist at Florida Atlantic University, explains, “They swim towards schooling fish and use their elongated pectoral fins as a brake. This raises their backend overhead…and they whip their tail towards the prey. The tip of it strikes so hard it can stun multiple fish! Thresher sharks have also been documented to perform sideways slaps in addition to overhead strikes. To our knowledge, thresher sharks are the only sharks to do this.” You can see it in action here^†. 

So, what gives these sharks the ability to do this? How do the vertebrae in their tails differ from other regions of their body and how does that change throughout their lives? 

Jamie and her colleagues set out to answer these questions by examining the vertebrae of common thresher sharks. They recorded nine different metrics of the vertebrae from fish of different sizes and ages. They included vertebral shape parameters like width and height and the number of internal mineralized structures that can influence the stiffness of the vertebrae. This information is important for determining the range of motion and what kind of force the vertebral column can tolerate. In the context of thresher sharks, the vertebral column at the base of the tail experiences extreme bending and was predicted to differ from the front of the body. But how?

Science often involves collaborations across disciplines, and this study is no exception. To do their work, Jamie and her team used what is called micro-computed tomography, or micro-CT scanning for short. It works in a similar fashion to CT technology used in human medical procedures by capturing 3D scans with x-rays. However, micro-CT machines use stronger x-rays and produce higher resolution images. Because the samples are not altered or destroyed by the process, this technology allows samples to be preserved for future studies and analyses. Jamie remarks about her collaboration with Dr. Tricia Meredith, director of the Florida Atlantic University High School Owls Imaging Lab housing the micro-CT machine, “This [Owls Imaging] lab collaborates with researchers both at FAU and externally, and individuals ‘pay’ for their imaging time with some sort of service. This can take the form of a guest lecture, lab tour, or mentorship of a high school student. It’s a wonderful way to make a professional lab space with high-end equipment accessible to those who cannot afford to pay.” Not only does this unique collaboration help to move science forward, but it also provides a return investment to the community. Even more, all 3D scans are made publicly available on MorphoSource^††, promoting additional collaborations in the future. 

Through analyzing these images, Jamie and her team were able to describe how the vertebral morphology and mineral structure varied between the front and rear regions of the shark and with increasing size of the shark. From this, they hypothesize that the front portion of the vertebral column is used for stabilization of the body and the rear portion to support the whipping motion of the tail. Because the length and use of the tail changes as the sharks mature, it also makes sense that the vertebral structure undergoes changes with size and age as a result. When common thresher sharks are young, their bodies are longer than their tails. As they reach adulthood, however, their tails are about the same size as their bodies. To put this into perspective, one shark included in their study measured nearly 8 ft (2.4 m) in length and had a tail nearly as long. That is one mighty big weapon!

When asked about future research, Jamie noted, “Our next steps are to look closely at the vertebrae from other species of sharks. We’re interested in how thresher shark vertebrae may compare to some other fast swimming species, like mako, white, and porbeagle sharks. We are also currently investigating the microstructures (or lack thereof, spoiler alert!) in the vertebrae of carcharhiniform sharks.” This work, as well as work with other large species like dolphins will add to our understanding of the linkage between form and function of skeletal tissue in these aquatic animals.

This study has all the hallmarks of cool science – a fascinating group of fishes, a collaboration that emphasizes accessibility and service, and results that showcase function is “form in action” even for animals on the extreme.  

It is a tail – and a tale – with purpose. 

The full manuscript can be found or downloaded here:
doi.org/10.1098/rsos.231473 (open access) 

^†Video source:
Thresher sharks use tail-slaps as a hunting strategy (Oliver et al. 2013) – doi.org/10.1371/journal.pone.0067380

^††3D image repository:
MorphoSource – morphosource.org