Karly E. Cohen, PhD

I am a postdoctoral fellow at the University of Florida in the Fraser lab looking at the evolution and development of teeth, denticles and odontodes. These are some of the earliest vertebrate traits (over 500 million years old)! Using an arsenal of bioimaging techniques I ask questions about fundamental laws acting on phenotypic evolution through the tools and adaptations of fishes, and how different lineages have solved common mechanical and ecological problems. 

I received my Ph.D. from the University of Washington and Friday Harbor Labs in 2022 and graduate from The George Washington University with a Masters in Science in Biology in 2019.

Current research

Some fish loose up to 20 teeth a day! 

Tooth replacement rates of polyphyodont cartilaginous and bony fishes are hard to determine because of a lack of obvious patterning and maintaining specimens long enough to observe replacement. Pulse-chase is a fluorescent technique that differentially colours developing mineralized tissue. We present in situ tooth replacement rate and position data for the oral and pharyngeal detentions of Ophiodon elongatus (Pacific lingcod). We assessed over 10 000 teeth, in 20 fish, and found a daily replacement rate of about two teeth (3.6% of the dentition). The average tooth is in the dental battery for 27 days. The replacement was higher in the lower pharyngeal jaw (LPJ). We found no difference between replacement rates of feeding and non-feeding fish, suggesting feeding was not a driver of tooth replacement. Lingcod teeth have both a size and location fate; smaller teeth at one spot will not grow into larger teeth, even if a large tooth nearby is lost. We also found increased rates of replacement at the posterior of the LPJ relative to the anterior. We propose that lingcod teeth do not migrate in the jaw as they develop; their teeth are fated in size and location, erupting in their functional position.

  

Why do we loose our edge?

 Most vertebrates are polyphyodont and continuously replace their teeth for the entirety of their life. Several clades have evolved diphyodont dentitions and only lose their teeth once as juveniles to make way for an adult dentition.

I am interested in the evolution of diphyodont dentitions and evaluating the selective pressures that led to the loss of polyphyodonty.

Complex dental patterns are linked to species radiations in several taxa —my research will explore how the evolution of dental complexity and jaw remodeling affects the rate of evolution across different vertebrate lineages. I hypothesize that the evolution of diphyodont dentitions is driven by constructional constraints of the jaws and that constant remodeling required of polyphyodont dentition cannot be maintained given the forces and stresses produced by chewing.

Check our my abstract in SICB or message me for my recorded talk!




Featured research

Dimorphic fluorescence in Pacific Spiny Lumpsuckers.

Joining the ranks of vertebrates that glow is the Pacific Spiny Lumpsucker, Eumicrotremus orbis, a subtidal species widely distributed across the North Pacific Ocean. Aside from their charismatic appearance, the Pacific Spiny Lumpsucker is known for its ventral suction disc that is used to stick to substrates amid changing currents and tides. Here we show that red lumpsuckers, which are usually male and a deep red color under broad-spectrum light, fluoresce bright red under ultraviolet (UV) light and blue light (360–460 nm), while green color morphs (usually female) do not. In all color morphs, the suctorial disc glows green-yellow. The red glow of the males matches the red glow of encrusting algae in their nesting areas, while the suctorial disc may be a signaling system. The green and red fluorescence observed in red lumpsuckers is the rarest fluorescent pattern and is only seen in 17 families of marine fishes. Pacific Spiny Lumpsuckers are cryptically colored under broad-spectrum light; our observed fluorescence suggests a potential avenue of communication and camouflage in an environment where red light is absent or rare.


Check out our story in the New York Times

Development of Lumpsucker Odontodes

Predation, combat, and the slings and arrows of an abrasive and high impact environment, represent just some of the biotic and abiotic stressors that fishes are armored against. The Pacific Spiny Lumpsucker (Eumicrotremus orbis) found in the subtidal of the Northern Pacific Ocean is a rotund fish covered with epidermal, cone-shaped, enamel odontodes.  We use micro-CT and SEM to reveal the morphology and ontogeny of the armor, and to quantify the amount of mineralization relative to the endoskeleton. 




Functional Homodonty and the conical tooth

If teeth all look the same we refer to them as homodont, and when they look different we refer to them as heterodont. However these measures of shape alone miss a great deal of variation within conical teeth. Looking at the selective pressures of load and stress we are creating statistical models to see how function enforces particular tooth shapes.  

Ontogeny of specialized filtering plates in silver carp

Silver carp are invasive filter feeders able to eat particles of food as small as 5 microns. This research looks  at the development and functional morphology of the filtering apparatus in silver carp. Looking at the morphology through classical anatomical techniques and micro-CT we  hope to answers questions about how silver carp are able to out compete filter feeders across trophic levels. 




Fluid dynamics of filter feeders  

Filter feeding fishes capture particles of food using a variety of mechanisms. this work focuses on filter feeding Asian carp and how their filtering mechanism differs from those previously described. 

Otocephalan epibranchial organs  

Eating small particles of food is hard. Fishes have to retain and aggregate particles in an efficient way. Epibranchial organs have independently evolved at least six times and are food aggregating structure found in certain teleosts. Morphologically complex and diverse this work analyzes the functional morphology of epibranchial organs to see how and why they different in form and function.