Cold weather may reduce Cuban tree frogs’ impact as they move north, UF researchers say

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 GAINESVILLE, Fla. — Invasive Cuban tree frogs are spreading through Florida, but a new University of Florida study suggests their impact could weaken as they move farther north, because colder weather seems to reduce their average size.

Smaller Cuban tree frogs would lay fewer eggs and be less likely to eat native frogs, said Steve Johnson, an assistant professor with UF’s Institute of Food and Agricultural Sciences. Cold weather may also shorten the frogs’ breeding season and life span.

The study, authored by Johnson and Monica McGarrity, a UF biological scientist, was published in the June issue of the journal Biological Invasions.

“This is a hint of a silver lining,” Johnson said. “We usually don’t discover things about invasive species where we say ‘hey, there’s a little bit of hope here.’ Usually it’s the other way around.”

The findings give wildlife managers and researchers in Southeastern states new reason to monitor local Cuban tree frog sightings and captures, he said. Further observation will confirm whether the frogs continue getting smaller as they spread north, and could provide valuable information to officials preparing for possible infestations.

The frogs were introduced to South Florida in the early 20th century, Johnson said. Today, they’re established in most of peninsular Florida, and individuals have been reported in Florida’s Panhandle, Alabama, Mississippi, Georgia, South Carolina, Texas, Maryland, Minnesota and Canada.

It’s unclear how far north the frogs could survive, but in extremely cold climates they would have to find warm places to ride out the winter, such as heated buildings, he said.

Though not dangerous to people, Cuban tree frogs pose a nuisance. They enter homes, secrete an irritating chemical from their skin, and trigger power outages by climbing into utilities equipment. They’re also suspected of depleting populations of native tree frogs.

“Cuban tree frogs are now the most commonly encountered tree frog in South Florida, at least in human-inhabited areas,” Johnson said. “It should be the native green tree frogs and squirrel tree frogs.”

In the study, Johnson and McGarrity measured the length of almost 350 Cuban tree frogs collected in Orange, Hillsborough and Alachua counties. Statistical analysis of these frogs showed that, on average, females were 53 millimeters (2.1 inches) long, males 43 mm (1.7 inches) long.

Prior studies showed Cuban tree frogs in South Florida’s Everglades National Park averaged 64 mm (2.5 inches) for females, 46 mm (1.8 inches) for males. Females from Cuba averaged 72 mm (2.8 inches), males 47 mm (1.8 inches).

“When we have these population values, that’s an average,” Johnson said. “There’s still going to be animals larger than average.”

The frogs can reach more than 120 mm (4.7 inches) long on their home turf, which includes Cuba, the Bahamas and the Cayman Islands. Females grow bigger than males, and a very large one can produce more than 15,000 eggs per year. Large females are also more apt to eat native frogs.

Cuban tree frogs come in many colors, including white, yellow, green, gray and dark brown. Apart from sheer size, their distinguishing features are unusually large eyes and toe pads, and warty skin.

Despite the problems they cause in Florida, Cuban tree frogs are sold as pets, Johnson said. He cautions people who buy the amphibians to make sure they can’t escape, and to never turn them loose in the wild.

“The issue (of invasive animals in Florida) is huge, and I think the general public doesn’t realize how great a problem we have,” he said.

For more information, see Johnson’s publication “The Cuban Treefrog, (Osteopilus septentrionalis) in Florida,” at http://edis.ifas.ufl.edu/UW259.

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Contacts:

Writer: Tom Nordlie, 352-392-2411, ext. 282, tnordlie@ufl.edu

Source:  Steve Johnson, 813-757-2273 (office) or 813-217-3692 (cell), tadpole@ufl.edu

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In this photo released by the University of Florida’s Institute of Food and Agricultural Sciences, amphibian expert Steve Johnson shows the size difference between two female Cuban tree frogs, at his lab in Plant City – Tuesday, July 14, 2009. The larger frog is typical of the size the animal reaches in its native range in the Caribbean; the smaller specimen is typical of invasive specimens captured in Central Florida. Johnson recently published a journal article suggesting the frogs reach smaller size in colder climates, potentially reducing their negative impact in the Southeastern U.S. (AP photo/University of Florida/IFAS/Eric Zamora)