UF Study: Young Frogs Delay Immune Response for Growth

Young frogs infected with a deadly fungus delay mounting a strong immune response and instead focus energy on growing quickly, according to research from the University of Florida published June 15 in the Journal of Animal Ecology.

Researchers built computer models using data from the coqui frog and the chytrid fungus Batrachochytrium dendrobatidis, which has driven amphibian declines worldwide. For frogs the size of a pinky nail, reaching larger size quickly reduces vulnerability to predators and improves survival and reproductive chances.

"We found that individuals invest in growth for as long as they can, and only switch to immune defenses when the pathogen becomes a real threat," said Zuania Colón-Piñeiro, lead author of the study.

The coqui frog hatches as a tiny adult rather than passing through a tadpole stage. Because juvenile frogs are too small to track individually in the wild, researchers used field and experimental data to model how frogs grow and respond to infection over a year.

Timing determines survival. Frogs born during favorable conditions when food is abundant can split energy between growth and immunity. Frogs born during cooler, drier periods face limited energy and higher stress.

"During the cool season, energy is so limited that even the best strategy doesn't lead to strong survival outcomes," Colón-Piñeiro said.

Environmental change could worsen these challenges. Longer or more frequent cool-dry periods may limit growth and reduce survival rates, said Associate Professor Ana V. Longo, senior author on the study.

Researchers say the framework could improve conservation strategies for species bred in captivity and released into the wild. The study included researchers from the University of Florida, the University of Puerto Rico and other institutions.