Lack of rainfall hinders frog reproduction, MU researcher says

Wednesday, July 4, 2012 | 2:30 p.m. CDT; updated 12:56 p.m. CDT, Thursday, July 26, 2012

COLUMBIA — Slowly and meticulously they approach the water as their headlights create tunnels of light in the darkness. They have spent all night searching. Pairs of black eyes begin to flicker in the light’s shine. In one bare-handed swoop, the frogs are stuffed into a box.

“We ice the pairs over night, and the next morning whoever is testing will warm them up a bit and run experiments for days with that group,” said Jessica Merricks, an MU biological sciences doctoral student.

Merricks is one of seven active lab researchers this summer under the direction of Carl Gerhardt, a curators' professor of biological sciences who studies American frog species. Merricks researches aspects of sexual selection in Missouri’s local frog population, specifically those of gray tree frogs. Her experiments, like others' in the lab, require her to collect pairs of mating frogs at night at a pond in Baskett Wildlife Area in Ashland and bring them back to the lab for further testing.

But on dry summer nights, pairs of frogs are nowhere to be found at the pond. Merricks said the behavior of most Missouri frogs depends heavily on the weather, specifically thunderstorms during spring and summer.

“Without the rain, we are just sitting and waiting,” Merricks said. “There is not a whole lot we can do when the frogs are not out. And so we are just at a standstill.”

Mating season for gray tree frogs typically begins in April and ends in early July. This year's breeding season started earlier than usual, with high numbers of reproductive pairs, but quickly dropped off as the drought developed. During a normal season, researchers can collect an average of 20 to 30 pairs of frogs per night. The lab has not seen any pairs at the pond since the third week of May.

Sarah Humfeld, a postdoctoral fellow in the division of biological sciences, has studied gray tree frogs for the past 10 years. Humfeld said this is the driest and most abnormal year she has seen.

“We may be at a point where ponds that are permanent may be drying up, and that would be affecting next year’s populations,” Humfeld said.

Gray tree frogs live in forested areas but require water to reproduce. During breeding season, male frogs typically stay near water and produce mating calls to attract females from the forest. 

However, this year's dryness is interrupting the process. The amphibians risk losing essential moisture through too much movement on dry ground, which could be deadly. Therefore, the females are staying put.

“We have several people in the lab doing different things, but most of us are dependent on collecting females,” Merricks said. “With it being this dry, the choruses are very weak and the males are not coming out so the females are not coming out either."

The lack of female frogs has led some researchers to gather frogs from other states. After hearing about the tropical storm in Florida last Thursday, Merricks and senior biological sciences major Adam Hasik packed the car and left the same day for Apalachicola, Fla., to collect frogs.

“One of the awesome things about this type of fieldwork is it is unpredictable,” Merricks said. “I am going to be down here as long as my frogs are calling because I am pretty desperate.”

Merricks has collected 14 pairs since her arrival.

“We have to test enough females so that individual variation is not skewing our data," she said.

Hasik received the Life Sciences Undergraduate Research Opportunity Fellowship to study the local species of gray tree frogs in Gerhardt's lab this summer. However, the dry conditions have made locating specimens difficult. With no luck at the Baskett pond, a colleague was able to collect six pairs of frogs in Rolla for Hasik's work this summer. Hasik needed at least 15 frogs to develop his research, though.

“It’s frustrating, but I know this is the way research works,” Hasik said. “It’s hit or miss. There is nothing you can control because this is nature we are dealing with.”

Supervising editor is Ann Elise Taylor.

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