A tiny tree frog provides clues to environmental changes that threaten all amphibians

One of the most threatened species is the Blanchard's cricket frog (Acris crepitans blanchardi), a tiny tree frog of ponds and bogs in the Midwest that was once widely found in northern Ohio, Wisconsin and Michigan. The frog has suffered huge population losses and now remains only in pockets of its former territory. A team of researchers at Case Western Reserve University and the Holden Arboretum recently published findings that the cricket frog's decline can be traced to man-made changes in the environment that may be damaging the frog's immune system. The study is scheduled to appear in next month's issue of the journal Biological Conservation. Blanchard's cricket frogs "have nearly gone extinct in their northern range, so we're almost forensically trying to understand what happened," said Mike Benard, a biology professor at Case. "This study suggests that changes we are making to the environment have the potential to make animals more susceptible to diseases and therefore may lead to population declines." The Blanchard's cricket frog is considered the most-aquatic of the tree frogs in North America, which makes it extremely vulnerable to polluted water and other man-made changes to their environment. The Case/Holden researchers found that changes in habitat produced differences in the cricket frog's immune defense system. Frogs from disturbed sites such as residential or agricultural land, for instance, were more susceptible to infections and diseases than frogs from more natural habitats. "We're seeing a lot of disease-related declines among amphibians, not to mention other groups of animals, such as bats plagued with white-nose syndrome and bees suffering from colony collapse disorder," said Katherine Krynak, a postdoctoral scholar in biology at Case and leader of the study. "This research shows that land use — farming or treating lawns with herbicides, pesticides and fertilizers — can influence traits that protect animals from disease," Krynak said.

Frogs used in the study were obtained from natural ponds surrounded by forest or prairie, and compared to frogs from more disturbed ponds in residential neighborhoods, near farms, athletic fields, parking lots and golf courses.

The researchers found measurable differences in skin bacteria between frogs that live in natural areas and ponds surrounded by residential and farm land.

"What we're seeing is the bacteria on the skin can vary markedly, depending on what people are doing to the environment that the frogs are living in," said David Burke, a scientist and research chair at Holden Arboretum in Kirtland.

Krynak said the research team will continue to study whether the findings with cricket frogs are similar to the environmental impacts on other amphibians, and also how the changes will impact generations of frogs to come.

"Not only may the environment be altering traits now, but it may be dampening the ability of a population to adapt in the future," Krynak said.

Source: Cleveland.com, December 21, 2015