Kingdom: Animalia

Phylum: Chordata

Class: Lissamphibia

Order: Anura

Family: Ranidae

Genus: Rana

Species: Rana pipiens

Range of Rana pipiens in North America.
This map is courtesy of Northern Prairie Wildlife Research Center

Frog Life Cycle

A) Fertilized eggs in gelatinous mass suspended in water
B) Water-bound, freshly hatched tadpoles
C) Tadpole undergoing metamorphosis
D) Tadpole developing hind legs
E) Developed froglet, ready for life on land with all four legs and lungs instead of gills
F) Mature frog has absorbed the tail and continues to grow

This image courtesy of Microsoft Encarta

Rana pipiens singing. Note the inflated vocal sacks.
This image courtesy of Northern Prairie Wildlife Research Center

To hear the beautiful call of Rana pipiens, use the controls below. (This requires a media player to play.) The recording is courtesy of Microsoft Encarta

Conservation Status

The northern leopard frog, R. pipiens, is common and is therefore not listed or proposed to be listed under the Federal Endangered Species Act (Frogs.org, 2001). R. pipiens do not appear on the IUCN (ICUN, 2000) list or the CITES (CITES, 2001) list of endangered and threatened species.

Little information is available as to the status of the species in the United States. The first widespread deformities and declines were recorded in 1995 in Minnesota (MPCA, 2001). However, in Alberta, Canada, the decline of northern leopard frogs has been well documented. The numbers of Rana pipiens started to decline in the 1960s, but the breeding populations remained healthy until the late 1970s. By 1990, only half of the remaining populations in Alberta were successfully breeding (Rasmussen, 2001).

This cartoon courtesy of Ray Rasmussen

Conservation Organizations

As the northern leopard frog is not considered an endangered or threatened species in the United States, there are only a few organizations concerned with their conservation.

The Great Lake Declining Amphibian Working Group is concerned with the declines of all amphibians and includes many good links to other organizations.

A Thousand Friends of Frogs is an organization under the care of the Center for Global Environmental Education at Hamline University. It is mostly a resource for teachers, with a mission of "connecting children, parents, educators, and scientists to study and celebrate frogs and their habitats."

The Minnesota Pollution Control Agency have a very useful website about frog deformations and issues related to sightings, causes of malformations, and education resources. The funding of the MPCA was cut by the Minnesota Legislature in July of 2001, however they continue to maintain this useful website.

Ray Rasmussen has a very interesting and useful site concerning the status of northern leopard in Alberta, Canada. It is interesting to see how our neighbors to the north have been treating this species.

Great Links

We highly recommend visiting the clickable map of North America at Northern Prairie Wildlife Research Center! Look for reports of malformed frogs and other amphibians in your state.

For basic information on R. pipiens, go to Frogs.org

For more in depth information, go to Northern Prairie Wildlife Research Center

More pictures of deformed frogs c an be found at The Minnesota Pollution Control Agency

For overall information on frogs and some specific information on Rana pipiens visit Encarta.com

More great links to other organizations can be found at the National Biological Information Infrastructure

Literature Cited

Conservation on International Trade in Endangered Species or Wild Fauna and Flora (CITES) 12 November 2001. http://www.cites.org (31 October 2001).

Donegan, Keenan. 28 March 1996. Rana pipiens (Leopard Frog). http://animaldiversity.ummz.umich.edu/accounts/rana/r._pipiens$narrative.html (29 October 2001).

Encarta. 2001. Leopard Frog Diving. http://encarta.msn.com/find/MediaMax.asp?pg=3&ti=761552464&idx=461539082 (31 October 2001).

"Frog (animal)," Microsoft® Encarta® Online Encyclopedia 2001
http://encarta.msn.com © 1997-2000 Microsoft Corporation. All Rights Reserved. (12 November 2001)

Frogs.org. 2000-2001. Species info for Northern Leopard Frog. http://www.frogs.org (31 October 2001).

Harding, James H. 2000. Amphibian and Reptiles of the Great Lakes Region. Ann Arbor: The University of Michigan Press.

International Union for Conservation of Nature and Natural Resources (IUCN). 2000. IUCN Red List of Threatened Species. http://www.redlist.org/ (31 October 2001).

Minnesota Pollution Control Agency. 11 July 2001. Frequently Asked Questions About Deformed Frogs. http://www.pca.state.mn.us/hot/frog-faq.html (29 October 2001).

National Biological Informational Infrastructure (NBII). 24 August 2001. FrogWeb: Amphibian Declines & Deformities. http://www.frogweb.gov/index.html (27 October 2001).

Northern Prairie Wildlife Research Center. 6 September 2001. Northern Leopard Frog, Rana pipiens. http://www.npwrc.usgs.gov/narcam/idguide/rpipiens.htm (31 October 2001).

Rasmussen, Ray. The Northern Leopard Frog. http://raysweb.net/specialplaces/pages/frog.html (10 November 2001).

Rosenberry, Donald O. 31 August 2001. Malformed Frogs In Minnesota: An Update. http://water.usgs.gov/pubs/FS/fs-043-01/ (29 October 2001).

Northern Leopard Frog
Rana pipiens

This image courtesy of the National Biological Information Infrastructure

Introduction

Rana pipiens, also known as the northern leopard frog, is a very important frog in the ecosystem. The northern leopard frog is a key animal in the food web. Frogs are more important to human survival and our current way of life than you may think! Frogs are so important that ecologists consider them to be bioindicators. In other words, scientists consider the health of a frog population to be a reflection of the health of the entire ecosystem (Encarta, 2001).

Distribution
The northern leopard frog, R. pipiens, is common in North America, inhabiting twenty-six states and much of Canada (see adjacent map).

Habitat
Rana pipiens live in a wide range of habitat, from open water and marshes to deserts and mountains (Frogs.org, 2000-2001).

Physical Characteristics
The northern leopard frog is medium in size, averaging from two to five inches long. They are green, brown, or both and have large dark irregular spots covering the dorsal part of their body (NPWRC, 2001). The skin covering R. pipiens is moist and smooth, and contains glands that secrete mucus in order to keep the skin from drying out. Northern leopard frogs also have glands in their skin that secrete poisons, which are strong enough to help them escape from their predators but are not harmful to humans (Encarta, 2001). Rana pipiens have eyes that are very keen, helping them not only capture prey but also to identify danger in their surroundings (Encarta, 2001). The northern leopard frog also has very powerful hind legs which are the main source of power in swimming and jumping. Also useful in swimming are the frog's webbed hind feet (Frog, 2001).

Food and Feeding
The diets of tadpoles and froglets differ from those of adult R. pipiens, with the young consuming herbivory such as algae as well as microscopic animals. Adults feed largely on insects, but also slugs, snails, and smaller vertebrates such as chorus frogs (Harding 156-157 and Donegan, 1996).

Relationship to other organisms in the ecosystem
Rana pipiens are common prey of birds such as herons, reptiles such as snakes, and mammals (including humans) (Donegan, 1996). Rana pipiens play an important role to humans. Besides being a source of food, frogs are used at every stage in their life for scientific study (Donegan, 1996). Furthermore, frogs play a key role in integrative pest management, eating agriculturally destructive insects.

Reproduction
Copulation occurs in the water between March and June. The females release eggs while swimming and the male, who attaches himself to the female with specialized thumbs, fertilizes the eggs. The fertilized eggs are then attached to either underwater plant material or simply placed on the bottom of the pond (Frogs.org, 2001). Each female lays up to 3,000 eggs, which hatch 10-20 days after fertilization (Rasmussen, 2001).

Development and Lifespan
The frog life cycle (shown to the left) is fairly simple. The frogs begin their lives as eggs, which are laid in clumps. When the eggs hatch the baby frogs are tadpoles and do not have limbs or lungs, like the adult frog. The tadpole undergoes metamorphosis, growing hind legs first, then front legs, and at the same time, developing a well defined head. The gills are replaced with lungs as the froglet adapts to life on land. On land the frog continues to lose its tail and grow in size. Rana pipiens reach sexual maturity in two or three years (Encarta, 2001).

Behavior
Rana pipiens are mostly nocturnal. Rana pipiens travel far distances away from water, but they must return to breed. In order to escape predators the northern leopard frog leaps into the water and buries itself in the mud or, if on land, takes several jumps into the air and then dives under vegetation for cover (Harding, 157). During the winter months northern leopard frogs hibernate.

Communication
The male northern leopard frog uses his croak to attract females and to establish territories (Donegan, 1996). The female northern leopard frog may use her croak if she is being retained by a male with whom she does not want to mate (Encarta, 2001). To hear the call of R. pipiens, use the controls on the left.

This image of a northern leopard frog jumping into water is courtesy of Microsoft Encarta

Conservation Issues

Malformed Frogs in Minnesota

This image of a malformed frog with two extra legs is courtesy of the Minnesota Pollution Control Agency

Malformed frogs have become a serious issue in recent years. Amphibian malformations have been recorded in 44 states and in nearly 60 species (NBII, 2001). Malformed frogs are found throughout the United States and Canada (see clickable map at Northern Prairie Wildlife Research Center), but first became a public issue in Minnesota. A high number of the malformed frogs are northern leopard frogs, R. pipiens (MPCA, 2001). For these reasons, we have chosen to focus on the issue of malformed frogs in Minnesota, and R. pipiens in particular.

Between 1995 and 2000, 13,763 R. pipiens were caught and reported in Minnesota, 6.5% of which were malformed (Rosenberry, 2001). Malformations include missing or extra limbs, digits and eyes, partial limbs, and malformed jaws, among other problems. These malformed frogs can still function, but not well (MPCA, 2001). Nearly all the malformed frogs found are juveniles, indicating that they rarely survive to adulthood.

Scientists do not know the exact causes of these malformations, and suspect that there may actually be many causes. Malformations at several sites in Minnesota have been linked to the presence of the parasite Ribeiroia ondatrae, a flatworm that burrows into tadpoles. Frogs heavily infected with R. ondatrae at these sites developed severe deformities (Rosenberry, 2001). However, R. ondatrae are not found throughout the state, leading researches to look for other causes as well.

Another cause linked to northern leopard frog malformations is pesticides. However, tests done at the research sites in Minnesota did not find high quantities of pesticides in the water (MPCA, 2001).

Researchers also believe that man-made chemicals other than pesticides may have an adverse affect on frogs as well. However, some studies show conflicting results. Some chemicals that are thought to be linked to malformations, such as methoprene, have been found not to affect the malformation of R. pipiens at levels commonly found in the environment (MPCA, 2001).

Another hypothesis is that the increasing amount of ultraviolet light hitting the earth’s surface may cause some malformations (Rosenberry, 2001). Most researchers believe that a combination of all of these factors result in the deformities found in so much of Minnesota.

The Minnesota Pollution Control Agency (MPCA) has led research efforts to try and locate the cause for frog malformations. The Governor of Minnesota and Minnesota Legislature gave funding in 1998, 1999, and 2000 for this research. The MPCA worked with the University of Minnesota, the National Institute of Environmental Health Sciences, the US Geological Survey, the National Wildlife Health Center and the U.S. Environmental Protection Agency on this project (MPCA, 2001). Unfortunately, funding for the study was cut in 2001.

This image of a frog with an extra hind leg is courtesy of the Minnesota Pollution Control Agency

Background image courtesy of Great Lakes Declining Amphibian Working Group

Authors: Johanna Mutti, Hannah Putnam, Alexandra "Coco" Shea
Last revised: 29 November 2001

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Earlham · Biology Department · Biology 26 : Biological Diversity