Pacific tree frog

Pacific Tree Frog
Conservation status
Least Concern  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Hylidae
Genus:	Pseudacris
Species:	P. regilla
Binomial name
Pseudacris regilla (Baird & Girard, 1852)
Synonyms
Hyla regilla

The Pacific Tree Frog (Pseudacris regilla) is a very common species of chorus frog, with a range from the West Coast of the United States (from North California, Oregon, and Washington) to British Columbia in Canada. Living anywhere from sea level up to over 11,000 feet, they are found in shades of greens or browns and even have been known to change between them. They live in many types of habitats and reproduce in aquatic settings. This species is also known as the Pacific Chorus Frog.

Anatomy and morphology

The Pacific tree frog can reach up to about 5 cm long from snout to urostyle. The males are often smaller than the females and have a dark patch of skin on their throat. This dark patch is the vocal sac which stretches out when a male is calling. These frogs can have highly variable color on their bodies. They can be anywhere from gray, brown, tan or bright green and can even change between them. They are usually a pale or white color on their bellies. They have many variations of markings on their back and sides that are usually dark and spotty. The one identifiable mark is a dark stripe that goes over the eye from the nose to the shoulder. Their skin is covered in small bumps. They have long legs compared to their bodies and they tend to be slender. Their toes are long and are only very slightly webbed. On the end of each toe, there is a round sticky pad that is used for climbing and sticking to surfaces.

Distribution, habitat and ecology

Pacific tree frogs are most common on the pacific coast of California, Oregon and Washington, but they are found anywhere from Baja California all the way up to British Columbia. They are also found eastward to Montana and Nevada. They love water, but they can also be found upland from ponds, streams, lakes and some times even further away from water. Their habitat consists of a wide variety of climate and vegetation from sea level to high altitudes. The tree frog makes its home in riparian habitat as well as woodlands, grassland, chaparral, pasture land, and even urban areas including back yard ponds. Eggs of the Pacific Tree Frog may be consumed by the Rough-skinned Newt, Taricha granulosa, and other amphibians.

Reproduction, development and behavior

The Pacific Tree Frog begins mating in early winter to early spring. Since these frogs are so widespread geographically, it is thought that their breeding season is determined by local conditions. When it is time, the males migrate to the water. They all call at the same time very loudly. This lures the females to the water and they mate. The females lay their eggs in clumps of 10-90 and usually put them on and under vegetation and leaf litter in the pond. Females usually lay their eggs in shallow, calm water that has little action around it. If they are not eaten, embryos will hatch into tadpoles within one to three weeks. The tadpoles feed on periphyton, filamentous algae, diatoms and pollen in and on the surface of the water. They feed using a beak like structure that helps scrape vegetation off surfaces and suction.

Metamorphosis usually follows about 2 to 2 1/2 months later, but experience raising these tadpoles shows that some may delay metamorphosis, changing up to 5 months after hatching. The survival rate of these delayed metamorphs is lower, and the evolutionary utility of this delayed metamorphosis is uncertain.

During the final stages of transformation when the tadpoles have 4 limbs and a tail, they stop feeding for a short time while their mouth is transformed from herbivorous to carnivorous. Then the tiny baby frogs emerge from the pond, sometimes measuring less than one centimetre.

The tree frog is mostly nocturnal, but they can sometimes be spotted during the day. These frogs spends a lot of time hiding under rotten logs, rocks, long grasses and leaf litter, where they are very difficult to see unless they move. When they hunt, their sticky pads allow them to climb on vegetation and other surfaces, but their usual role is as ambush predators. Much of their diet consists of spiders, beetles, flies, ants and other insects and arthropods; they can and do eat insects that are almost as large as they are, and will expand their bodies slightly to accommodate these meals.

If you do happen to catch these frogs, you will need an aquarium and water. Also go down to your local pet shop and purchase some medium to small sized crickets, or just do it the cheap and fun way and catch them out in your backyard. Make sure you watch them eat the crickets. They ambush their prey so well.

Pseudacris regilla matures quickly, and are likely able to mate in the next season after metamorphosis. Captive specimens do mate more prolifically 2 seasons after metamorphosis, however. Predators include snakes, raccoons, herons, egrets, and other small mammals and reptiles.

Evolutionary history

The evolutionary history of these frogs is a very interesting one that has recently been changed to better suit tree frogs. Amphibians themselves are thought to have descended from the lobe-finned bony fishes. These fishes had an ossified skeleton and emerged from the water as they developed limb girdles and terrestrial characteristics such as lungs and a neck.

It is hard to figure out an exact frog lineage because of the lack of fossil record. The habitat in which these animals lived was moist and decay was quick. This was not helpful in preserving biological clues. The family of Hylidae is somewhat recent, appearing around 50 million years ago. The genus Hyla was close behind appearing just after the dinosaurs went extinct. This genus originated in South America and expanded to the north into Mexico and eventually into North America. There was then a rise in sea level and the connection between the northern and southern populations was gone. They have been separate ever since, and have become genetically distinct from one another.

For this reason, the genus Hyla has been split into three separate categories. Aris, Limnaoedus and Pseudacris. This is where the current confusion has taken place. Although the Pacific Tree Frog has carried the scientific name of Hyla regilla for many years, the most current consensus among scientists is that they should actually be Pseudacris regilla. This is still not agreed upon completely, and in the future we will see what becomes of these names.

Green and brown color morphs

One of the most interesting features of these frogs is their ability to change color from brown to green. Previously, it was thought that there were two different fixed colors that an adult tree frog could be. Now it has been found that some of them are actually able to change between the two. They can also change from lighter to darker, shift from patterned markings to pure colors and vice versa, and even display combinations of colors, brown/green being the most frequent.

These color changing morphs are triggered not by color change in their environment, but a change in background brightness. This type of environmental change would be caused by seasonal fluctuation. A full change in the dorsal coloration of a color morph can take anywhere from weeks to months, but initial changes can occur in just a few days. This has been shown to be a very useful cryptic survival feature for these frogs.

Skin color is produced via pigment cells called chromatophores. There are commonly three types of chromatophores found in amphibians: 1. Xanthophores - These contain yellow, orange, or red pigments and are found uppermost on the dermis; 2. Iridophores - These lie below the xanthophores and function by reflecting and scattering white light up through them; in the case of Pseudachris regilla and many other North American frogs, iridophores reflect blue light through the yellow pigment cells above to create a green frog; 3. Melanophores are the deepest pigment cells and are responsible for the presence of black and brown pigments.

A rare, recessive "blue morph" is known. There is currently one housed at the Humboldt State University Natural History Museum in Arcata, California. See link. [1] It has been suggested that this mutation inhibits the xanthophores' ability to produce yellow pigments, thus the normally green frog (possibly of the non-color-changing type) appears blue.

Conservation status

These frogs are the most common frogs on the west coast of North America. Although the Pacific Tree Frog remains abundant, there has been a large increase in amphibian declines. Most populations of tree frogs appear healthy, but there is some evidence of declines. The cause has not been fully understood, but pollution, the introduction of exotic species and habitat loss are very high on the list of factors. Some ways to stop amphibian declines are by respecting and protecting amphibian habitat, as well as supporting laws and legislation that help to do this. Another important way is to help limit pollutants that will end up in amphibian habitat (usually from agriculture and urban run off) by boycotting companies who are heavy pesticide users.

The most direct and effective way to protect frogs is personal responsibility. Do not pour chemicals or pollutants down storm drains, or into amphibian habitat. Don't use pesticides in on your lawn or garden or bleach in decorative fountains, especially if you live near amphibian habitat or a waterway.

Side view showing a color variant.

Care and Feeding

Children often consider tadpoles to be nearly irresistible pets, but very few of these pets tend to survive the experience. The best approach is to leave the tadpoles in nature.

Failing that, about 4 tadpoles per gallon is a good rule of thumb for tank size. The chosen tank needs to avoid the usual power filters, which can hurt tadpoles, in favor of gentle sponge filters or similar "dirt magnet" filters. Careful 1/3 to 1/2 water changes using a siphon will still be necessary on a regular basis until the tank's nitrogen cycle stabilizes (usually about a month), and nitrate test kits or displays are a must. Overly cloudy water or a dead tadpole should also trigger a prompt water change, or the entire tank can be lost quite quickly.

In a reversal of normal aquarium practice, snails can transmit parasites, and should be avoided; while algae growth should be allowed or even encouraged. Some floating weeds are also a good idea, as they give the tadpoles a place to rest near the surface. This becomes even more important during metamorphosis. Pacific Tree/Chorus Frog tadpoles will do reasonably well on a sprinkled diet of pure spirulina from health food stores, though some supplementation with fish fry foods like Sera Micron appears to help.

These tadpoles are somewhat challenging to raise through to adulthood. The key milestone is when he tadpoles begin to grow front legs. At this point in time, they need to be able to rest on or near the surface of the water, as their gills are transforming into lungs and they need to be able to gulp air periodically. Their ability to climb on cage surfaces and leave the cage during the final stages of metamorphosis is even more troublesome. This is usually fatal, as human homes are very dry. Finally, their size makes them difficult to feed immediately after metamorphosis; wingless fruit flies are the best option, though they will eventually grow large enough to eat crickets and even mealworms.

Parents who are not enthralled with these difficulties should arrange to release the tadpoles back into nature as soon as their front set of legs begin to develop. Calm, shallow waters are best, and the frogs will also need low-lying vegetation and ground cover nearby once they transform.

Would-be frog keepers will also find the post-metamorphosis moisture balance in the tank itself to be challenging, since the tiny metamorphs can dry out very quickly, but cannot live exclusively in water as they will exhaust themselves and drown. A wet/dry tank is best.

Regional importance

In 2007, the pacific chorus "tree" frog was named the state frog of the State of Washington. The tree frog is also a very important in all of the regions where it is found because it is a keystone species. Many other species such as garter snakes depend upon its abundance as a prey item for their survival.

External links

• Fact sheet, taxonomic details, distribution maps, slideshow, and images of Pseudacris regilla at ZipcodeZoo.com.
• Californiaherps.com description - Includes detailed description, photos, recordings of calls
• mister-toad.com Pacific Tree Frog description - Description of the ecology of Pacific Tree Frogs with photographs, audio and video.
• http://www.npwrc.usgs.gov/resource/herps/amphibid/species/hylareg.htm