Coquí

A coquí on a leaf with penny for size comparison

Eleutherodactylus spp. are small tree frogs that can vary in color. These frogs can be a mixture of brown, yellow, green, and gray on the top and the bottom side of their body is either white or yellow. The eye color is a variation of brown and gold. They can range in size from 15–80 millimetres (0.59–3.15 in).[2] The first word of the species' scientific classification is the genus name Eleutherodactylus which is Ancient Greek and Modern Greek for "free toes", referring to the fact that this species has no webbing in between its toes.[3] The coquí have special disks instead of webbing on their feet, differentiating them from many other types of frogs. These disks help the coquí climb and stick to trees and leaves.

Coquís live in tropical areas and have been discovered in different levels of elevation. They can be found at up to 1200m in elevation,[4] usually in humid mountain forests or in dry forests. According to the Invasive Species Compendium, the Eleutherodactylus coquí shares the nests of common native species of birds like the "bananaquit (Coereba flaveola portoricensis), the Puerto Rican bullfinch (Loxigilla portoricensis), and the Puerto Rican tody (Todus mexicanus)".[5] Coquís tend to be in their natural habitats in the forests but it is also common for the species to appear in human territories such as houses, parks, and near bodies of water.

Coquís belong to the Eleutherodactylus genus which in Greek means free toes. Eleutherodactylus contains over 200 species that naturally occur in the southern United States, Central America, South America, and the Caribbean.[6]

Seventeen described species of coquí inhabit Puerto Rico. In 2007, a new species, the coqui llanero, was officially named Eleutherodactylus juanariveroi.[7]

Kingdom: Animalia

Phylum: Chordata

Class: Amphibia

Order: Anura

Family: Leptodactylidae

Genus: Eleutherodactylus

Eleutherodactylus coqui Thomas 1966[8]

The various species of coquí control the populations of herbivorous insect species in their local environments. Their voracious appetites focus on arthropods like cockroaches, spiders, crickets, and beetles. Larger coquí species may feast on lizards and fellow frogs.

A study on mass balance and ecosystem processes discussed how animals affect plant and soil pools through excretion. One of the roles coqui frogs play is by greatly increasing nutrient pools in plant biomass and in litter.[9]

The coquí frog gets its name from the mating call of the male, which sounds like coquí, or "co-kee". Male coquí frogs use their call to attract female frogs and establish their territory. When multiple male coquís are found in the same area, they challenge each other's domain by song. The coquí frog that loses usually flees and tends to relocate to another area or compete for territory elsewhere. Male coquís start singing around the time the sun sets and continue throughout the night, until dawn.

Although coquís can reproduce all year long, their breeding is at its peak during the wet season, which is around April to October. Female frogs tend to lay about 15 to 40 eggs roughly five times a year. Coquís differ from most other frog species because coquís lay their eggs in terrestrial plants, whereas other frog species usually lay their eggs in water.[3] The males gather up the eggs and provide protection in a nest, guarding them. Because the eggs must remain moist, male coquís will periodically leave the nest to collect moisture in order to keep the eggs hydrated when it appears they are beginning to dry out. The male coquí frog keeps the eggs moist by touching them with his moist skin.

The coquís and their fellow members of the Eleutherodactylus genus have a life cycle unique among frogs. While most frogs begin their lives as tadpoles (complete with a small tail that aids the juvenile frog in swimming before they develop legs), the coquís are hatched as tiny frogs with short tails, thereby entirely skipping the free-living larval stage. This life cycle, in which the tadpole stage is completed within the egg itself, is referred to as direct development. Due to the lack of an external tadpole stage, bodies of water are not necessary for female frogs to lay their eggs.

Once they reach their adult stage, most coquís do not live longer than a year, although the National Wildlife Federation states that some coquís have been found to be as old as six years.[5]

The decline of coquí populations has accelerated since the introduction of the Batrachochytrium dendrobatidis fungus.[10] This pathogenic fungus has been extremely devastating towards amphibian populations, as the pathogen impairs the permeability of the skin. The coquís found in El Yunque are resistant to the B. dendrobatidis fungus at the expense of their size, which reduces the aptitude to survive in the wilderness (Burrowes, Longo and Rodríguez 2007). Individual coquí species that carry this fungal resistance are most often found in regions where the B. dendrobatidis fungus is concentrated and the coquí diet is thus more abundant. Although the fungus prefers humid environments, infection is more frequent in drier climates, because coquís tend to cluster in humid sub-areas within such climates, thereby increasing the chance of spreading the pathogen.[10]

The environmental degradation caused by Hurricane Hugo in 1989, the hurricane in 1998, and the two-year drought from 2015 to 2017 have all had a massive impact on the 28,000-acre (110 km²) El Yunque rain forest in Puerto Rico, including the resident coqui frogs. Increase in average temperature has already increased the incidence in coqui frogs of Batrachochytrium dendrobatidis, a chytrid fungus that reduces the reproductive capability and increases mortality of the Coqui frogs.

The more recent hurricanes Irma and Maria in 2017 also hit Puerto Rico.[11] Irma did not directly strike Puerto Rico, but Maria impacted Puerto Rico directly two weeks later, and devastated the forest on a massive level. Specific conditions prevented some sites from massive destruction, but 53% of the Puerto Rican El Yunque rainforest[12] was devastated. Hurricane Maria destroyed the forest canopy that had shielded the ground from the sun and left the ground shaded and cool, and the ground temperature has thus increased by 4 °C. Small changes in release and uptake of carbon dioxide create much larger changes in its atmospheric concentration. The warmed ground areas have shown less root recovery from hurricane damage.

Several of the more vulnerable coquí species (particularly E. eneidae and E. karlschmidti),[13] whose ranges are contained within the lower altitudes of the El Yunque National Forest, are in imminent danger of extinction. This has increased the range and success of the more resilient species of coquí frog, especially the Red Eyed Coqui, which can withstand drier periods, fluctuations in temperature, and other conditions. In the Luquillo Mountain range, the Mountain Coqui was not previously endangered, but as a result of Hurricane Maria, it might have become so.

By 2009, the USGS established that the species had been identified in Puerto Rico, Hawaii, St. Croix, St. John, St. Thomas, Florida, and the Dominican Republic.[14]

Coquís have become established on the Big Island of Hawai'i, where they are considered an invasive species. Coquí population density in Hawaii can reach 20,000 animals per acre, affecting 50,000 acres (20,000 ha). Eradication campaigns are underway on Hawaiʻi and Maui.[15][16][17]

The Eleutherodactylus coqui was introduced to Hawaii around the late 1980s. This species found its way to the Hawaiian Islands by hiding in plants that were being transported to the islands. Studies have shown that the species has increased nutrient cycling rates, and actually helped some native species which previously existed in low-nutrient conditions.[18]

The coquís have a very small number of predators (rats and some lizards); as a result, the coquí population has increased over time. Another factor in the population increase is that they can breed continuously throughout the year. As a result, the Eleutherodactylus coquí has had a negative impact on native species by increasing competition with native birds, and other frogs. The expansion of the Eleutherodactylus coquí has forced other creatures such as bats to seek alternatives, as they compete for food at higher elevations. Birds and bats were not greatly affected by the introduction of coquís to the island until the frogs started appearing on higher ground. The species is also feeding on native spiders and insects that are close to extinction.

Coquís have been officially listed as an invasive species of concern in Colombia.[19] The species has also been found in California, mostly in plant nurseries, though as of 2014 had not been known to have established a stable population.[20]

Overall, attempts to limit or control the coquí population where they are invasive have been unsuccessful. In Hawaii, the intentional transportation of frogs is a class C felony, and coquís are labeled as pests.[21]

One action that appears to be effective in decreasing the coquí population in commercial areas is a hot shower treatment on nursery plants. The hot shower works as a disinfestation treatment for not only the Eleutherodactylus coquí eggs, but also for adult coquís.[22]

Only a few chemical treatments are legal. Citric acid can be legally used in Hawaii, though the chemical must directly contact coquís, perhaps even multiple times. However, the citric acid may adversely impact plants and cause unseemly spots.[5] Other substances that are used to control the species are hydrated lime and caffeine. Eradication techniques include hand-capture, and spraying with a 12% solution of citric acid, along with a certification program for nurseries to prevent them from acting as centers of contagion.[15]

• Common coquí
• Fauna of Puerto Rico
• List of amphibians and reptiles of Puerto Rico

• Hawaiian Ecosystems at Risk project (HEAR), Eleutherodactylus coqui
• ITIS
• State of Hawaii, Department of Agriculture, Coqui Frog Information
• University of Hawaii, Control of Coqui Frog in Hawaii