It's a frog-eat-frog world: professor studies cannibalistic tadpoles

Research could aid in treating human muscle-wasting diseases

RELEASED: September 24, 2009

By Leigh Ivey

DANVILLE, KY—Although many Centre College professors and students are engaged in scientific research, not many are currently spending their time studying tadpoles that dine on their peers.

This is just what Centre's new assistant professor of biology Dr. Brian Storz is doing, however.

His work explores the muscle enlargement in cannibalistic spadefoot toad tadpoles in order to further his research of skeletal muscle growth regulation.

Over the past eight years, Storz has discovered that although all spadefoot toad tadpoles "hatch with the 'typical' tadpole phenotype, some can attain a drastically different morphology, that of carnivore and cannibal."

(A phenotype is the appearance of an organism that results from the interaction of its genotype and its environment. A genotype is the genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits.)

In this naturally evolved polyphenic system (a system in which multiple discrete phenotypes are produced from the same genotype), some tadpoles have evolved the ability to enlarge their skeletal muscle while transforming into cannibals.

"The non-cannibal tadpoles eat mostly detritus (small particles of disintegrated material) and algae, while the cannibals are eating mostly protein," Storz says. "They're shooting around the pond, eating other tadpoles, eating fairy shrimp—basically, anything they can catch, they'll eat. They even chew on your toes if you walk into the pond barefoot."

The cannibals show up to a two-fold increase in the growth rate of specific muscles. Along with having much shorter intestinal tracts and different beaks than their non-cannibal siblings, they also show massive enlargement of their jaw muscles.

"I'm interested in understanding how the cannibals are turning on cell growth," Storz says. "Because if we can figure about how they've evolved the ability to turn on cell growth, we may be able to apply this knowledge to people who have muscular dystrophy, people who have cardio myopathies, people who have some sort of muscle-wasting disease. We might be able to use this system and apply it to human health."

And so far, his results "go against all theory for how muscle growth is regulated."
  
The current skeletal muscle growth models are based on adult stem cells. Muscles are made up of fibers that are grouped together, and just below the cell membranes of these fibers are dormant adult stem cells, termed myosatellite cells.

When muscle damage occurs, these stem cells become activated, start replicating themselves and grow new muscle.

"The model of how muscle growth occurs is that these stem cells start to proliferate and can either fuse to themselves, forming a new muscle fiber, or fuse to existing muscle fibers," Storz says. "So initially, our studies were geared towards understanding how these adult stems cells were regulating muscle growth in the cannibals, relative to the non-cannibals."

To investigate this question, Storz exposed tadpoles to the chemical BrDU, which becomes incorporated into the DNA of newly created nuclei, produced from adult stem cells. 

"We used the BrDU to label newly created nuclei in the cannibals and non-cannibals," he says. "We were then able to see how many new nuclei they're creating. You'd expect that there would be a lot in cannibals because they have enlarged muscle, relative to non-cannibals, but it turns out there's no difference at all."

This may represent a novel way that muscle growth is occurring. "Somehow growth is occurring, but it's not occurring by the creation of new cells, which is completely at odds with the current model of skeletal muscle growth," Storz says.

Knowledge of the factors regulating muscle growth is required to understand how the use of stem cells can combat many diseases, including cancer, cardio myopathies and muscular dystrophies.

"This is why I was funded by the American Heart Association," Storz explains. "They're interested in not only basic cardiovascular research but also in trying novel systems to see if we can discover something new."

Storz will be continuing his research here at the College, and this fall, he will be assisted by Centre student Megan Gatewood '10. Their collaboration focuses on an experiment Storz conducted to study tadpole morphology in the presence of their cannibalistic siblings.

"It's well documented that tadpoles can modify their morphology in the presence of predators," Storz says. "They can change the size of their tail or their tail coloration if they're in the presence of a predator so that the predator will strike at their bright tail instead of their head, and the prey will survive."

What is not known is whether cannibal tadpoles that are siblings of non-cannibal tadpoles can induce this modification in morphology.

To investigate this question, Storz conducted a large experiment, rearing non-cannibals in the presence of cannibals, as well as collecting non-cannibals from natural ponds with and without the presence of cannibal tadpoles.
 
Much of Gatewood's work will involve analyzing the data from this experiment.

"Most of my biology classes have had labs that have taught me lab procedures which are applicable in this research," she says. "And my evolutionary biology class introduced me to some of the terms and concepts I'm going into much more detail with now."

Gatewood is but one of many Centre students who collaborate with professors in scientific research each year. The personal education that she and other students are given, she believes, has prepared her for a future in the field of biology.

"In the long-term, I'd love to teach biology at Centre or a school very similar to Centre," she says. "This community has nurtured my interests and helped me in innumerable ways, and I'd love to give back when I'm able and more qualified."

To learn about other professor-student research projects at Centre, click here and here.  

For students interested in joining "Team Spadefoot," contact Dr. Brian Storz at brian.storz@centre.edu.

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