Forest Fragmentation May Dwarf and Deform Island’s Coquís

by Suzanna Engman

Biology professor Carla Restrepo holds a coquí that has been chemically treated with a process called clear and satin, which removes natural pigments and adds dye to reveal the bone (red) and cartilage (blue). The right front toes of the coquí show severe deformities, while the left front toes have fewer deformities.

When University of Puerto Rico Biology Professor Carla Restrepo and her former graduate student Johanna Delgado-Acevedo measured coquís from deforested areas in the northern karstic region of Puerto Rico, they found them to be smaller, just as they had hypothesized. But after clearing and staining them, they detected an alarming surprise. Many of the coquís, tiny frogs endemic to Puerto Rico and the Virgin Islands, exhibited skeletal abnormalities.

“We started to find incompletely developed, missing, and deformed bones. The preliminary data indicated that prevalence of these problems was higher in the fragmented habitats,” Restrepo reports.

With forest fragmentation, caused by human destruction, both larger and smaller animals tend to suffer the highest population losses and extinction risks. Scientists reason that smaller species have trouble moving from one forest patch to another to access resources whereas bigger species have fewer resources to sustain them within the smaller patches.

Restrepo and Delgado’s investigation of two common coquí species was carried out in nine sites divided into heavily forested, moderately forested, and pasture habitats.

Coquís from the pastures were indeed 5-10 percent smaller than those from areas with 70 percent or more foliage cover. “I focus on body size as a key ecological variable determined by genetic processes and developmental mechanisms, which can be strongly influenced by the environment. A case in point is shown in humans, whose average height has increased over the last century because food and health conditions have improved. You can apply this logic to forest fragmentation but in the opposite direction,” Restrepo says. In other words, if resources are scarce, a species’s body size may get smaller over a period of time, and this, in turn, may have an impact on other traits of the organism.

While studies on four continents have uncovered, in Restrepo’s words, “an amazing increase” in the number of frogs with deformities, for example those with a fifth limb or those with extra digits, the UPR-RP research documents, for the first time, deformities in coquís, a type of frog that does not have a tadpole stage. Eleutherodactylus, the genus to which coquís belong, emerge from eggs as fully metamorphosed hatchlings, or froglets.

Restrepo is also engaged in two other branches of ecological research. She investigates carbon dioxide sequestration associated with landslides in Guatemala and Mexico. When released into the atmosphere, CO₂ contributes to the greenhouse effect, and scientists are searching for ways to store, or sequester, CO₂ to mitigate global warming. Landslides may provide a natural means of CO₂ sequestration.

Restrepo’s third project, a collaboration with a multidisciplinary team, funded by the Office of the Dean of Graduate Studies and Research, examines how interactions between human and natural networks may influence the resilience of the Río Grande de Arecibo watershed, which supplies about 100 million gallons a day to the San Juan metropolitan area and has been listed as an Impaired Water Body by the Environmental Protection Agency. The research team joined efforts to understand, and possibly avert, problems that lead to losses of ecological services. The project fosters research in computer science, biology, geography, education, and environmental science, and may iniate a Spatial Analysis Center for investigators who study tropical landscapes.