Pseudacris regilla
All text and photographs © Michael F. Benard
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Natural History of the Pacific Treefrog Pseudacris regilla All text and photographs © Michael F. Benard Indtroduction and Identification
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A shallow puddle in Napa County, CA, where Pacific treefrogs bred. In February this puddle was full of eggs. However, it dried long before any of the treefrog tadpoles could escape the puddle by metamorphosing. |
An ephemeral pond in Napa County, CA, where Pacific treefrogs breed. This photo was taken in February when the pond was at its deepest. Predators of pacific treefrogs at this pond include predaceous diving beetles, giant water bugs, and garter snakes. |
A permanent pond in Napa County, CA, where Pacific treefrogs breed. This pond contains predatory invertebrates, such as odonate nymphs, as well as large centrachid fish like bluegill sunfish. |
 A mating pair of pacific treefrogs in amplexus. The male is clinging to the back of the female. |
While the male pacific treefrogs call away at the pond, females approach and select males to mate with. Research has shown that female pacific treefrogs prefer to mate with males that consistently call earlier than the other males around them (Whitney and Krebs 1975). Additionally, larger male frogs are more likely to mate with female frogs than smaller males (Benard, in press). During the peak of the breeding season, huge numbers of males will all be out on the same nights. When two males get too close to each other, they will often switch from using "advertisement" calls to "encounter" calls to drive the other males off (Brenowitz and Rose 1999). While the encounter call may drive off the other male, female pacific treefrogs are not attracted to the encounter call. If one does not back down, there may be a physical attack by one frog on another.
When a female approaches a male, the male will move onto her back, and grasp her under her forelimbs with his forelimbs in a position known as "amplexus". The female will now swim into a pond and lay eggs on vegetation, debris and other structures. As the female lays eggs, the male will release sperm to fertilize the eggs. Females will lay multiple egg masses that range in size from one or two eggs to over 100 eggs. |
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A male pacific treefrog missing its rear right foot. Despite its wound, this male was seen frequently throughout the 2005 breeding season. I observe a few frogs each year with similar wounds. Many more frogs have scars on their back in the shape of the jaws of snakes. |
The breeding season is not just a time of fun for pacific tree frogs. A variety of predators will capture adult pacific treefrogs, including snakes and raccons. One common predator I have observed hunting breeding adults is the giant water bug, Lethocerus americanus. These enormous insects capture the frogs with their raptorial forelimbs, and use their piercing mouthparts to inject digestive toxins into the frogs.
After the breeding season is over, the pacific treefrogs disperse back into the habitat surrounding their pond. There is little evidence on how far from their breeding pond the adults will move. However, I have observed a few individually-marked adults up to 300 meters from the breeding pond. Both male and female pacific treefrogs will return to the same pond to breed. Some may live through as many as four breeding seasons. However, only 10-20 percent of the adults will survive from one breeding season to the next (Benard, unpublished data, Jameson 1956). |
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Giant water bug nymph, one of many predators on pacific treefrog tadpoles. |
Pacific treefrog eggs may take several days to hatch. Upon hatching, the tadpoles are at risk from a host of predators that view pacific treefrog tadpoles as a tasty meal. However, generations of natural selection have prepared the tadpoles for these threats. Tadpoles can detect chemical cues from these different predators, and initiate defensive responses that are specific to each kind of predator.
For example, pacific treefrog tadpoles develop enlarged tails when they smell predaceous diving beetles; these enlarged tails serve as a lure to distract strikes from the body of the tadpole toward the tail (Benard 2006). However, when tadpoles smell bluegill, they develop a shape that improves their swimming speed: shallow tails and deep tail muscles. These distinct responses to each type of predator represent adaptations to each predator's foraging strategy. Beetles are sit-and-wait predators, while fish can chase their prey for short distances. |
Bluegill sunfish, another predator. |
In the presence of predatory insects, tadpoles develop deep tails (top tadpole). In the presence of predatory fish, tadpoles have shallow tails (bottom tadpole). Tadpoles that are not exposed to cues from predators are intermediate in shape. |
Predaceous diving beetle larvae eating a tadpole. |
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Predators are not the only threat tadpoles face. Because pacific treefrogs commonly breed in emphemeral ponds, a major source of mortality for tadpoles is pond drying. When these ponds dry early in the year, any pacific treefrog tadpole that cannot metamorphose into a small froglet will be killed.
However, tadpoles have an adaptation to improve their chance of surviving in these ephemeral habitats as well. When pacific treefrog tadpoles detect that their pond is drying, they can accelerate their development rate so that they metamorphose earlier in the year. While this does not always save the tadpoles, it can improve their chances of survival in some ponds. |
Metamorphosing pacific treefrog. |
Metamorphosing pacific treefrog. |
Common garter snake (Thamnophis sirtalis), one of the predators that feed on metmorphosing pacific treefrogs. |
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Conservation Issues
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A note about names
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Literature Cited Croes, SA, and RE Thomas. 2000. Freeze tolerance and cryoprotectant synthesis of the pacific treefrog, Hyla regilla. Copeia. 2000:863-868. Blaustein, AR, PD Hoffman, DG Hokit, JM Kiesecker, SC Walls, JB Hays. 1994. UV Repair and resistance to solar UV-B in amphibian eggs: a link to population declines? PNAS. 91:1791-1795. Brenowitz, EA and GJ Rose. 1999. Female choice and plasticity of male calling behaviour in the Pacific treefrog. Animal Behaviour. 57:1337-1342 Fisher, RN, and HB Shaffer. 1996. The decline of amphibians in California�s great central valley. Conservation Biology. 10:1387-1397. Jameson, DL. 1956. Growth, dispersal and survival in the pacific treefrog. Copeia. 1956:25-29. Jameson, DL, JP Mackey, M Anderson. 1973 Weather, climate, and external morphology of pacific tree toads. Evolution 27:285-302. Jameson, DL and S Pequegnat.. 1971. Estimation of relative viability and fecundity of color polymorphisms in anurans. Evolution 25:180�194. Matthews, KR, KL Pope, HK Preisler, RA Knapp. Effects of nonnative trout on Pacific treefrogs (Hyla regilla) in the Sierra Nevada. Copeia 2001:1130-1137. Stebbins, RC 2003. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003. Wente, WH and JB Phillips. 2003. Fixed green and brown color morphs and a novel color-changing morph of the pacific treefrog, Hyla regilla. American Naturalist. 162:461-473. Wente, WH and JB Phillips. 2005a. Microhabitat selection by the Pacific treefrog, Hyla regilla. Animal Behaviour. 70:279-287. Wente, WH and JB Phillips. 2005b. Seasonal color change in a population of pacific treefrogs (Pseudacris regilla). Journal of Herpetology. 39:161-165. | ||||
| Attention All text and photograhs on this website are copyright Michael Benard. If you have any inquiries about using any of this material, or for any other questions, I can be contacted by email at mfbenard 'at' gmail dot com. |
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