N.C. State University and Yale University researchers uncovered the developmental pathway to one frog species carnivorous diet helping us to understand our own guts in the process.
As summers light rains knock on our doorstep, many of us may spend time gazing into pools and ponds, watching tadpoles shimmy along the waters bottom, scooping up algae and detritus with their friendly maws. Most young frogs are strict vegetarians, peaceful puddle dwellers content to eat pond scum.
But not the tadpoles of a frog known as the Budgetts frog. These ferocious predators appetites often include fish and small mammals as adults. As tadpoles they even eat their own siblings.
Its for good reason, said Nanette Nascone-Yoder, NCSU associate professor of molecular biomedical sciences.
Budgetts tadpoles grow up in nutrient-poor, temporary pools that could dry up fast, she explained. To get the nutrition they need, they often eat each other because theres no other food available.
Chomping away at ones siblings takes some fancy footwork on the part of digestive tract development.
Most tadpoles have a typical vegetarians long, simple gastrointestinal tract for their nutrient-poor diet, Nascone-Yoder said. We became interested in Budgetts tadpoles because they have more mammal-like GI tracts.
Nascone-Yoders lab examined the developmental pathway from herbivores to carnivores in these frogs. The researchers exposed developing frogs to chemicals that mimic GI tract genetic mutations. They found when the meat-eating Budgetts tadpoles were exposed to certain chemicals, their GI tracts developed to be more herbivorous. This helped the researchers pinpoint the developmental mechanism to carnivorousness.
They also exposed vegetarian African clawed frogs to chemicals that cause the opposite effect and found the plant-digesting tracts develop to be more like those of their meat-eating cousins.
While chemically switching frog guts may sound like a sinister pastime, Nascone-Yoder points out this research gives us insight into our own stomachs. She describes the intricacies, the loops, valves and textures food passes through for animals to get the nourishment they need to survive.
The shape of each GI tract is so complex; its exquisite, she said. There is an incredible diversity of morphology of digestive tracts across species. Each tract adapted for each organisms diet.
Clues to birth defects
Nascone-Yoder believes that by studying frog guts, researchers eventually can solve humans genetic disorders. We want to see what goes wrong in these shapes to give rise to birth defects in humans, she said.
There are a significant number of birth defects in humans that involve alterations in GI-tract topology. Its possible that if we hit on these alterations as we did with these frogs, we could start to understand how you can derive such defects.
Chemical genetics, or using chemicals to mimic genetic mutations like Nascone-Yoders team does with these tadpoles, is a relatively cost-effective way to explore genetic disorders. Researchers employ chemical genetics to help advance malaria drug developments, understand brain, eye and ear formation, and cancer research.
Though tadpole guts might seem a far cry from humans, Daniel Fergus, a molecular geneticist with the N.C. Museum of Natural Sciences, says model organisms like the Budgetts frogs are important to making big advancements in research on humans.
Model organisms can share a lot of characteristics with humans, but they are affordable, grow quickly, and are much easier to work with than humans, he said. This means we can study the developmental systems of tadpoles, fruit flies or zebrafish in a few weeks.
It would take several years for us to study these same systems in humans.
For now, Nascone-Yoders team is sticking with tadpoles. These species have other unusual features, such as extremely large embryos with very rapid development, she said. We believe these features will make them powerful new animal models for understanding human development not only in the digestive organs, but throughout the body.