Karly Cohen

Who I am

I am currently a postdoctoral fellow at the University of Florida’s Department of Biology. My research dives into the world of hard skeletal tissues – their evolution, how they develop and the mechanics behind them. I received my PhD in biology in 2022 from the University of Washington, having researched the development, morphology and mechanisms of feeding in fish. I developed successful research and mentorship programmes at both the Seattle-based university and its marine field station, Friday Harbor Laboratories, by exploiting the unique advantages of each location. A microcosm of life and research, Friday Harbor Labs hosts CT scanners, microscopes, research vessels and a range of students, scientists and researchers – truly spectacular resources that I am grateful to have experienced.

My research integrates diverse methods for exploring morphology (the way things look) and function (the way things work) in a broad range of organisms. For instance, I use fish as a model to bridge the gap in our knowledge between ecological and evolutionary patterns underlying some of the earliest vertebrate traits: teeth and scales. Ratfish, also known as chimaeras or ghost sharks, are some of the strangest chondrichthyans. Instead of single teeth they have a fused beak, and while other sharks boast a coat of armour made from skin denticles, ratfish are naked. My aim is to find out where ratfish breed and lay their eggs so that I might better understand how these oddities develop. I use cutting-edge technology like RNA-seq to compare the early dentition of these cartilaginous fish to others that are known. My hope is that by finding ratfish nursery sites we can establish a better natural history record for some of the Pacific Northwest’s most enigmatic fish.

Where I work

In 2018, I relocated to the University of Washington’s Friday Harbor Laboratories, situated on an island about 80 miles (130 kilometres) north of Seattle, nestled between the Haro Strait and the Bering Strait. As I’m from the East Coast, this was my inaugural exposure to the unique biodiversity of the Pacific Northwest. Friday Harbor Labs is unique among marine stations in that it has cutting-edge technology right at the water’s edge. There’s no substitute for observing an organism just 50 feet (15 metres) from your lab, enabling you to photograph and study it in tanks. By trawling, fishing and tide-pooling, I encountered my first skate egg case, dogfish shark, large purple urchins and gumboot chitons. Later that year, I had the privilege of diving beneath the surface to explore historic trawling lines with a fresh perspective. It was during this experience that I first encountered the spotted ratfish, a species that would become a focal point for my research in the years ahead.

Many shark species, including ratfish, lay eggs in specific areas that increase their reproductive success, often in shallow waters in a harbour. However, numerous other shark species do not inhabit these warm, safe and shallow zones, which makes it challenging to track their breeding, egg-laying and hatching locations. In the waters surrounding Friday Harbor, ratfish ascend from the depths to regions where we can dive and trawl. Over recent years, our surveys have unveiled their egg-laying activities in our shallow waters.

Studying the ratfish at San Juan Island grants us invaluable insight into the life and reproduction of benthic chondrichthyan species. By identifying their nursery and breeding grounds, we begin to outline potential sites elsewhere. This research also offers fresh perspectives on shark biology that could help us to understand the roles of other deep-sea sharks and predict the whereabouts of their nursery areas.

What I do

My research focuses on teeth – essential vertebrate traits unified by a developmental toolbox that enables cutting-edge genomics tools to be applied to questions of evolution and development. Teeth are one of the most readily identifiable vertebrate traits. Much of what we know about human evolution is based on fossilised teeth. Similarly, the teeth of other vertebrates serve as an important clue in identifying the relationship between the morphology of the organism and its environment. Fish teeth are strikingly diverse and their shape, damage patterns and material properties represent their ecologies. I am currently studying the spotted ratfish, an incredibly abundant chimaera in the Pacific Northwest. Spotted ratfish are distant cousins of modern sharks, but they diverged nearly 400 million years ago, evolving novel tooth plates and a head tenaculum.

The spotted ratfish presents a unique opportunity for studying a benthic shark. At Friday Harbor and in other parts of the Washington coast, this typically deep-sea species ventures into shallower waters to lay its eggs. I am locating these nursery sites to establish a more comprehensive record of its population and natural history. My curiosity extends to examining its embryonic development, unravelling the process by which ratfish develop their distinctive traits and predicting potential environmental influences. Our typical research days involve ventures onto the water, either aboard marine research vessels to collect population data and egg cases or utilising remotely operated vehicles to film and explore the seabed. Back in the lab, I process tissue to extract genetic and cellular information about growth and development. The footage captured by the remotely operated vehicles helps us to compare the habitats of different nursery sites, enabling us to craft interactive virtual reality exhibits that enable viewers to engage with ratfish, even from land.