September 8, 2010

The Scientist: Amy McCune

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From your roomate’s goldfish to the trout in Cayuga Lake; for Prof. Amy McCune, ecology and evolutionary biology, these ordinary specimens provide a glimpse at a world of great diversity.

“My organism of choice is fish,” she explained. “There are fish fossils everywhere there are sediments.”

McCune uses fish to study the evolution of diversity.

“What greater thing is there in biology than to understand where biological structure and function come from?” she asked.  In particular, McCune studies the radiation of an extinct group, known as thesemionotids, who lived in eastern North America during the Late Triassic and Early Jurassic of the Mesozoic era.

The Mesozoic era occurred from 250 million to 67 million years ago.  The period is more commonly frequently paired with dinosaurs because it was the time of their extinction.  However, semionotid fish generated many species of fish during the Mesozoic in the deep basins of rift valley lakes.  Sedimentary fossils from New Jersey and Connecticut indicate that their evolution generated huge diversity in a relatively short period of time.

To explain the creation of such diversity, McCune compares the evolution of extinct semionotid fish to living cichlid fish, living in the Great African Rift Lakes.

“Semionotids are analogous to cichlids,” she explained.  The two groups share similar characteristics and environments.

Like semionotids, cichlids evolved rapidly, and in Lake Victoria, over 300 species of cichlids have emerged in less than 12,400 years.  This rate of “speciation,” the creation of new species, exceeds many other organisms.

Although debate persists, scientists frequently attribute the great evolution of cichlids to factors, such as sexual selection and discrepancies in resource utilization.  For instance, certain characteristics may lead female fish to select certain male traits; over generations, these male traits may become magnified in a group of fishes, leading to the generation of a new species.

By understanding speciation in living cichlids, McCune works to unravel the evolution of semionotids.

In addition, McCune investigates the evolution of “phenotypes,” observable traits, like body morphologies and structure.

“Even as a grad student, I was interested in the generation of complex traits,” she said.  She acknowledged that her most exciting research explores the evolutionary origin of the swim bladder, a common organ in multiple lineages of fish.

This organ allows each fish to control its underwater buoyancy, allowing the creature to maintain its current water depth without exerting energy while swimming.  If the fish secretes air into the bladder, the fish becomes less dense relative to water, and it rises toward the surface. If the fish withdraws air, it sinks toward the floor.

Some swim bladders also function in communication, generating and receiving sound.

Darwin once speculated that the swim bladder is actually a transitional structure, either an ancestral form of a lung or an alternative branch in the evolution of the same structure.  This belief likely emerged from the perceived image of the organ – most people believe it is  a sac.

“It surprised me how much structure the swim bladder has; it’s always thought to be just a sac,” McCune explained. “You can see how ornate it is – just like a lung … swim bladders are incredibly diverse in their morphology.”

McCune hopes to unravel the evolutionary history of swim bladders in order to determine if swim bladders are actually modified lungs. This investigation will involve comparing the developmental genes of both organs and assessing the morphological similarities between the organs, such as the source of their blood supply.

“I was interested in biology as a kid,” McCune described. “In college, I wanted to be a marine biologist.”

Her alma mater Brown University did not provide its undergraduates with an organized program for evolutionary biology, but McCune quickly realized that evolution penetrated every discipline in biology.

“I started thinking, this is really amazing,” she related. “All function and structure in biology can be understood with evolution.

Original Author: A. Drew Muscente