Trophic Morphology & Function

So far, most of my research has focused on trophic morphology, which I find interesting for a few reasons, the foremost being that feeding is the most obvious way the physical anatomy of an organism interacts with its environment. As a result, trophic mechanisms are a prime target for natural selection. Unlike most mammals, which rely on their tongues, multiple types of teeth, and a single fairly simple jaw lever for the capture and initial processing of food, fish have evolved a wide variety of mechanisms for capturing food. These can include highly protrusible upper jaws, a secondary set of pharyngeal jaws, elaborate musculoskeletal lever systems for generating suction and biting, and even a wide array of filtration systems that range from comb-like gill rakers to porous pads. These systems can vary dramatically, even within species, which makes them great for studying how evolution and the environment interact.

The two species I have done the most work with have wildly different trophic systems. American paddlefish, which regularly grow to 5 ft and whose closest relatives are sturgeon, are ram suspension feeders. That means they force water through their mouths by swimming forwards, and filter zooplankton from the water column using gill rakers. Unlike most filter feeding fish, their gill rakers are behind other bones called the branchial arches, and the flow of water over the branchial arches creates vortices that aggregate the prey at the base of the rakers. In paddlefish, the jaws play very little role in feeding, other than being open and occasionally "pumping" in what may be attempts to clear the gill rakers of algae or foodstuffs that have gotten stuck. Among large filter-feeders this unusual system appears to be most similar to basking sharks, and American paddlefish are the only living acipenseriform fish (paddlefish and sturgeon) that filter-feed.

Threespine stickleback, on the other hand, have a many bones and muscles that work in concert to accommodate different prey types. These include a highly mobile premaxilla (upper jaw bone) that can slide forward when feeding on zooplankton to create a tube, as other parts of the trophic system expand the oral cavity to generate suction. When feeding on benthic invertebrates, like insect larvae, small crustaceans, and mollusks, dentary (lower jaw) and premaxilla work together to bite and manipulate prey. Sticklebacks also have gill rakers, which can be long and numerous in populations that rely more on zooplankton, or short and relatively sparse in stream or shallow pond populations that tend to feed more on benthic inverts. Many populations are also sexually dimorphic, with females tending to be more adapted to feeding on zooplankton.

​Population Dynamics & Life History

In my current work, I am looking at microevolution, population dynamics, and life history of 20 small populations of arctic charr, a salmonid closely related to the brook trout common in the eastern US and Canada (pictured above). These populations have apparently persisted for a few thousand years in small caves formed from lava rock in northern Iceland, and none of them has a population of more than a few hundred individuals. I will be using life history data collected over the last decade, and genetic data, to determine how environmental and biotic community variation has influenced the population dynamics and life history evolution of these populations.

Integration & Modularity

Integration and modularity are two sides of the same coin. Organisms are necessarily made up of parts, each of which is associated with other parts. These associations can take many forms: they can be functional, or genetic, or developmental, or some combination of these. Each group of associated parts can be referred to as a module, and their associations as integration. I am interested in how different modules and systems are functionally integrated, and how patterns of integration can influence the trajectory of evolution. I am also currently studying the functional implications of disruptions to integration patterns between modules, and whether these hinder performance or open up niche-space that was previously unavailable.

Patterns of Rapid Evolution

Much of my research focuses on contemporary evolution within populations. While the public perception of evolution is still that it it takes an extremely long time, a large body of research has accumulated over the past few decades showing that significant evolution over short timescales as short as a few generations is pervasive. Rapid adaptation can occur in response to abrupt environmental changes, but also cause abrupt shifts in the biotic community and environment. Because of their short generation times, stickleback are a great species for studying introductions and have been used to study both adaptive responses to environmental change, and more recently, environmental feedbacks on evolution. I am currently using an introduced stickleback population to study changes (or stasis) to patterns of integration among trophic modules.