Dusky gopher frog (Lithobates sevosus)

Description

Dusky gopher frog fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
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Dusky gopher frog description

The dusky gopher frog (Lithobates sevosus) is considered to be North America’s most highly endangered frog species ^{(3) (4)}. A rather stocky amphibian with a warty back, it is named for its dark colouration and its tendency to shelter in the burrows of the gopher tortoise, Gopherus polyphemus ^{(3) (5) (6)}.

The upperparts of the dusky gopher frog are always dark, but can vary from almost uniform black to grey or brown, with large, darker brown spots. There are also dark spots on the chin and chest ^{(3) (5) (6) (7)}. The dusky gopher frog has a large head, with a particularly large mouth, and there are prominent ridges down the back ^{(3) (6)}. Its limbs are short and thick, and the hind feet have only a minimal amount of webbing between the toes ⁽³⁾.

The female dusky gopher frog is generally larger than the male ^{(2) (3)}. The tadpoles of this species are greenish-brown ⁽³⁾ and measure up to about 7.4 centimetres in length ⁽²⁾.

The call of the male dusky gopher frog is described as a distinctive, deep, continuous ‘snore’ ^{(3) (6) (7)}. Some males have been known to call while underwater ⁽³⁾. The dusky gopher frog was previously thought to be a subspecies of the gopher frog (Lithobates capito), but genetic studies have since shown it to be a distinct species ⁽⁸⁾.

Also known as

dark gopher frog, dusky crawfish frog, Mississippi gopher frog.

Synonyms

Lithobates sevosa, Rana areolata sevosa, Rana capito sevosa, Rana sevosa.

Size

Length: 5.6 - 10.5 cm ⁽²⁾

Dusky gopher frog biology

The adult dusky gopher frog feeds on a variety of insects and other prey, including beetles, grasshoppers, spiders and worms. Its large mouth probably also enables it to eat larger prey items, such as other frogs and toads ^{(2) (3)}. In contrast to the adults, the tadpoles of this species feed on plant matter ^{(1) (6)}. When threatened by a predator, the adult dusky gopher frog defends itself by inflating the body, covering its eyes with its front feet, and secreting a pungent, bitter, milky liquid from the prominent warts on its back ^{(2) (3) (6)}.

Glen’s Pond typically holds water from December or January until June or August ⁽⁹⁾, with the dusky gopher frog usually breeding there between December and April. However, heavy rains from tropical storms or hurricanes may stimulate earlier breeding, in late summer or autumn ^{(2) (3) (6) (10)}. Male dusky gopher frogs usually arrive at the breeding pond before the females, setting up and defending territories, and calling to attract a mate ^{(2) (3)}.

The female dusky gopher frog usually lays between 500 and 3,000 eggs, attaching them to aquatic vegetation, floating wooden debris or small trees ^{(2) (3)}. The tadpoles take between 81 and 179 days to develop, depending on the water temperature ^{(2) (3) (10)}, and the size at which metamorphosis occurs can vary widely between years ⁽²⁾. The immature frogs, known as ‘metamorphs’, usually emerge from the pond between May and July, and leave along specific migratory pathways ⁽²⁾. After breeding, the mature adults also move away from the pond, returning to their underground retreats ⁽¹¹⁾. Male dusky gopher frogs reach maturity at about 6 to 8 months old, but females do not mature until about 24 to 36 months old ⁽⁹⁾.

This species usually lives for less than seven years ^{(6) (9)}. The breeding success of the dusky gopher frog varies greatly between years, but is often low due to the breeding pond drying up before the tadpoles have time to fully develop ⁽¹⁰⁾.

Dusky gopher frog range

Until recently, the dusky gopher frog was known from just one site, at Glen’s Pond in Harrison County, Mississippi ^{(1) (2) (5)}. However, individuals have now also been recorded from two other locations, at McCoy’s Pond, 50 miles east of Glen’s Pond, and at Mike’s Pond, 20 miles to the west ^{(1) (3) (4) (6)}.

The dusky gopher frog was formerly more widespread along the coastal plain of the southern United States, from eastern Louisiana, through southern Mississippi and into Alabama ^{(1) (2) (3) (5) (7)}.

Dusky gopher frog habitat

This species inhabits upland, sandy longleaf pine (Pinus palustris) forest, favouring areas with a relatively open canopy and abundant ground vegetation ^{(1) (2) (3) (5) (6)}.

The dusky gopher frog breeds in fairly shallow, isolated, temporary ponds containing both emergent and submerged vegetation. These breeding pools only contain water for part of the year. In addition to occupied and unoccupied gopher tortoise burrows, the adult dusky gopher frog will also shelter in the burrows of other small animals, as well as in holes in stumps ^{(1) (2) (3) (5) (6)}.

Dusky gopher frog status

The dusky gopher frog is classified as Critically Endangered (CR) on the IUCN Red List ⁽¹⁾.

Dusky gopher frog threats

The dusky gopher frog has disappeared from most of its former range due to the loss and alteration of its habitat. Less than two percent of the original longleaf pine forest now remains, largely as a result of urbanisation, forestry activities, agriculture and grazing ^{(1) (3) (6)}.

This species has quite specific habitat requirements, needing temporary, fish-free pools in relatively open, grassy forest, as well as an abundance of burrows in which to shelter. It therefore does not adapt well to changes in its environment, such as the alteration of temporary to permanent ponds, the introduction of predatory fish, and fire suppression, which increases canopy cover and alters ground vegetation ^{(1) (5) (6) (12) (13)}. A decline in gopher tortoises, and therefore tortoise burrows, is also a potential threat ⁽⁶⁾.

With only one main breeding population, which is restricted to a single site and estimated at just 60 to 100 mature individuals, the dusky gopher frog is extremely vulnerable to extinction ⁽¹⁾. Although two more populations have now been discovered, these are small and isolated, and are not known to be stable breeding populations ^{(1) (3)}. The main population at Glen’s Pond is under continued threat from urbanisation, including the construction of a highway and various development projects ^{(1) (4) (5)}. In addition to further reducing the dusky gopher frog’s habitat, these developments may make it more difficult to use fire as a habitat management measure. Chemicals used to maintain a proposed golf course could also pose a threat ^{(1) (5)}, and the adult frogs do not appear to enter an area to the north of the pond where the forest has been clear-cut ⁽¹¹⁾.

The dusky gopher frog is also threatened by two fungal diseases, including chytridiomycosis, a potentially fatal disease threatening amphibians worldwide ^{(1) (14)}. This species’ small, isolated populations have low genetic variation and are susceptible to inbreeding ^{(1) (5) (14) (15)}, and its low reproductive success is a further threat to its survival ⁽¹⁾. As the dusky gopher frog’s breeding success is highly dependent on rainfall and the length of time for which the breeding pond is filled ^{(1) (5) (10) (14)}, this species could be negatively affected by climate change, which may potentially alter rainfall patterns.

Dusky gopher frog conservation

The dusky gopher frog is listed as Endangered under the U.S. Endangered Species Act ⁽¹⁶⁾ and is classified as Endangered in the state of Mississippi ^{(1) (2)}. The population at Glen’s Pond occurs within De Soto National Forest, but is not entirely protected from the threat of habitat loss ^{(1) (14)}.

A Gopher Frog Recovery Team has overseen a range of conservation actions for this rare amphibian ⁽¹⁾, and a recovery plan is being written ⁽¹⁴⁾. Conservation measures for the dusky gopher frog include habitat management, supplementing the breeding pond with extra water in dry years, raising tadpoles for release, constructing or restoring new breeding sites, and moving eggs to other suitable sites. It will also be important to research the species’ breeding habits, ecological requirements and diseases ^{(1) (2) (3) (5) (6) (14)}. Surveys are needed to determine the status of the recently discovered populations, and to discover if the dusky gopher frog still survives in any other locations ⁽¹⁾.

Removing trees around ponds and introducing more natural fire regimes may help improve habitat for the dusky gopher frog ^{(3) (13)}, while a ‘buffer zone’ around Glen’s Pond may help to protect important terrestrial habitat for the adult frogs ⁽¹¹⁾. The reintroduction of gopher tortoises would also benefit this species ^{(2) (3)}. Although captive breeding attempts have not always been successful ⁽⁴⁾, new methods led to the successful hatching of over 1,400 dusky gopher frog tadpoles in captivity in 2010 ⁽¹⁷⁾. The conservation efforts for this highly endangered frog need to be continued and expanded if the last remaining populations are to survive ⁽¹⁾.

Find out more

Find out more about the dusky gopher frog and its conservation:

• AmphibiaWeb:
  http://www.amphibiaweb.org/
• The Nature Conservancy: Mississippi - Dusky Gopher Frog:
  http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/mississippi/explore/dusky-gopher-frog-profile.xml
• U.S. Fish and Wildlife Service - Mississippi Gopher Frog:
  http://www.fws.gov/southeast/publications/gopher.pdf

More information on amphibian conservation:

• Amphibian Ark:
  http://www.amphibianark.org/
• IUCN/SSC Amphibian Specialist Group:
  http://www.amphibians.org/

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Glossary

Emergent

Aquatic plants whose stems and leaves extend beyond the water’s surface.

Genetic variation

The variety of genes within a particular species, population or breed causing differences in morphology, physiology and behaviour.

Inbreeding

The breeding of closely related individuals. An inbred population usually has less genetic variability and this is generally disadvantageous for its long-term survival and success.

Metamorphosis

An abrupt physical change from the larval to the adult form.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Territory

An area occupied and defended by an animal, a pair of animals or a colony.

References

1. IUCN Red List (April, 2011)
   http://www.iucnredlist.org/
2. AmphibiaWeb (April, 2011)
   http://www.amphibiaweb.org/
3. Dorcas, M. and Gibbons, W. (2008) Frogs and Toads of the Southeast. University of Georgia Press, Athens, Georgia.
4. AmphibiaWeb: Zoos play a vital role in amphibian conservation (April, 2011)
   http://amphibiaweb.org/declines/zoo/index.html
5. U.S. Fish and Wildlife Service - Mississippi Gopher Frog (April, 2011)
   http://www.fws.gov/southeast/publications/gopher.pdf
6. The Nature Conservancy: Mississippi - Dusky Gopher Frog (April, 2011)
   http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/mississippi/explore/dusky-gopher-frog-profile.xml
7. Conant, R. and Collins, J.T. (1998) A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin, Company, New York.
8. Young, J.E. and Crother, B.I. (2001) Allozyme evidence for the separation of Rana areolata and Rana capito and for the resurrection of Rana sevosa. Copeia, 2001(2): 382-388.
9. Richter, S.C.and Seigel, R.A. (2002) Annual variation in the population ecology of the endangered gopher frog, Rana sevosa Goin and Netting. Copeia, 2002(4): 962-972.
10. Richter, S.C., Young, J.E., Johnson, G.N. and Seigel, R.A. (2003) Stochastic variation in reproductive success of a rare frog, Rana sevosa: implications for conservation and for monitoring amphibian populations. Biological Conservation, 111(2): 171-177.
11. Richter, S.C., Young, J.E., Seigel, R.A. and Johnson, G.N. (2001) Postbreeding movements of the dark gopher frog, Rana sevosa Goin and Netting: implications for conservation and management. Journal of Herpetology, 35(2): 316-321.
12. Thurgate, N.Y.(2006) The Ecology of the Endangered Dusky Gopher Frog (Rana sevosa) and a Common Congener, the Southern Leopard Frog (Rana sphenocephala). Ph.D. Thesis, University of New Orleans, Louisiana, USA.
13. Thurgate, N.Y.and Pechmann, J.H.K. (2007) Canopy closure, competition, and the endangered dusky gopher frog. The Journal of Wildlife Management, 71(6): 1845-1852.
14. U.S.Fish and Wildlife Service (2009) Mississippi Gopher Frog Recovery Action Plan. U.S. Fish and Wildlife Service, Southeast Region, Jackson, Mississippi. Available at:
    http://ecos.fws.gov/docs/action_plans/doc3100.pdf
15. Richter, S.C., Crother, B.I. and Broughton, R.E. (2009) Genetic consequences of population reduction and geographic isolation in the Critically Endangered frog, Rana sevosa. Copeia, 2009(4): 799-806.
16. U.S. Fish and Wildlife Service: Species Profile - Mississippi Gopher Frog (Rana capito sevosa) (April, 2011)
    http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=D031
17. Association of Zoos & Aquariums (2010) Amphibian Conservation: 2010 Highlights and Accomplishments. Association of Zoos & Aquariums (AZA), Maryland, USA. Available at:
    http://www.aza.org/amphibian-news/