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Voyageur's Best Features of 2001

A question about tadpoles

A question about tadpoles
Scientists study tadpoles at Long Lake Conservation Center
by John Grones  |  July 10, 2001

Visiting Long Lake Conservation Center is always an interesting and valuable experience. There is always activity, not only in the wild, but with the many visitors attending the center. The last week in May and early June was no exception.

Upon arriving at the center in late May, I discovered a group of individuals from Northern Kentucky University studying tadpoles. It was also the last week for school groups. The fifth grade from Lino Lakes was visiting and they did some studying of their own.

The tadpole study is being conducted by Dr. Richard Durtsche, an Assistant Professor of Biology at Northern Ketucky University. Durtsche, a University of Minnesota-Duluth graduate, is familiar with the area, because he has been coming to a cabin on Wilkins Lake since 1972. Over the years, Durtsche recognized eight species of frogs in the area, so when he decided on a Tadpole Foraging Ecology study, Long Lake Conservation Center seemed like the perfect spot.

Conditions were perfect at that time of year. The ponds were filled with thousands of tadpoles, which is exactly where I found Durtsche and his three students when I arrived at Long Lake Conservation Center. Waders were a necessity and all three Northern Kentucky University seniors, Taya Dickman, Jennifer Quammen, and Andy Pfaehler had just finished collecting tadpoles in a pond north of the parking lot. After Professor Durtsche finished up by recording the pH level and temperature of the water they headed back to the temporary lab in the old mess hall.

The study produced four species of tadpoles on the site. They discovered American Toads, Wood Frogs, Spring Peepers and Boreal Chorus Frogs. How they identify species is actually quite detailed. The mouth parts are the key. Only under a microscope can scientists determine species. Using a formula already established, Professor Durtsche and his students were able to count the number of labial tooth rows above and below the beak to determined what they had found.

The tadpoles in the pond north of the parking lot turned out to be toads. There were no frogs in this pond. This came as no surprise to the group. "Toads will not put their eggs in ponds where wood frogs have laid their eggs," said Durtsche. "The wood frog tadpoles will eat the toad tadpoles." The group was able to find some frogs in another pond near the Northstar Lodge to study. Each student came with their own set of questions and a specific area of study. For Taya Dickman, the question was, "Does water temperature have anything to do with the sex of the tadpole?" Taya found the answer to this question in other literature, but this lead to several other questions. Her study focused on the individual behavior of the tadpoles.

Taya looked at the time tadpoles spent doing various activities. Beakers were prepared with different tadpole densities in multiples of three. She noticed a stress response at higher densities when the tadpoles bumped into each other. Since this occurred more often in higher densities, the growth rates of the tadpole slowed.

This is significant, since ponds in many cases are temporary and often dry up and many of the tadpoles would not develop in time. Jennifer Quamman took a close look at the tadpole's diet. She determined that 70% of their diet is unidentified detritus or organic material. In layman's terms, it is the muck or scum on the bottom of the pond made up of dead material. The other 30% is algae. Jennifer determined this by observing the stomach contents under a microscope. The other question Jennifer had was: Where does digestion take place? This will be determined by cutting up the intestinal tube into five parts and studying them in the lab back at the University.

One of the intriguing mysteries about these animals has to do with the fact that as the young mature,they go from being herbivores to carnivores. With most animals, this doesn't happen. It does with frogs.

Andy Pfaehler was in charge of an experiment. His goal for the two weeks was to find out how much the tadpole eats and how fast the food passes through. Andy created a form of tadpole jello. The jello consisted of crushed algal discs mixed with agar, a gelatin-like substance. Pink beads were added to the substance to help monitor the passage rate of the food.

As is the case with most of the study, the results must wait until further lab work takes place at the university. The team returned to Northern Kentucky in late June and they will work until early fall.

As Professor Durtsche reflected on his stay at Long Lake Conservation Center one moment stood out. "A group of wrestlers were at the camp and they became curious. They started helping collect tadpoles and started asking all kinds of question."

Questions - the beginning of all scientific studies.