Mississippi gopher frog

Mississippi gopher frog
Conservation status
Critically Endangered  (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Order:	Anura
Family:	Ranidae
Genus:	Lithobates
Species:	L. sevosus
Binomial name
Lithobates sevosus Goin & Netting, 1940
Synonyms
Rana sevosa Goin & Netting, 1940

The Mississippi gopher frog or dusky gopher frog (Lithobates sevosus) is a rare species of true frog. It is endemic to the southern United States, and its natural habitats are temperate, coastal forests and intermittent freshwater marshes. This secretive frog is on average 3 in (8 cm) long, with a dark brown or black dorsal surface covered in warts.

Taxonomy

The Mississippi gopher frog was originally described as a new species (Rana sevosa) by Coleman J. Goin and M. Graham Netting in 1940. Subsequently, it was considered one of several subspecies of the more widespread and common gopher frog (Rana capito). It was re-elevated to species status in 2001.

Range

The Mississippi gopher frog was once abundant along the Gulf Coastal Plain in lower Louisiana, Mississippi, and Alabama—from east of the Mississippi River Delta to Mobile Bay. However, it has not been seen in Alabama since 1922 or in Louisiana since 1967. Presently, only two known populations exist; with about 100 frogs to be found in Glen’s Pond, Harrison County, Mississippi. The other population is less dense and spread out through the surrounding wetlands, recently found to concentrate around Mike’s Pond, Jackson County, Mississippi. Currently, the range of Rana sevosa is decreasing at a dramatic rate due to urban sprawl, deforestation, and even fire suppression that destroys the possibility of sunlight reaching down to the wetlands, critical for the growth of the frogs' immediate habitat. Currently, the two known populations of Rana sevosa are separated by only 32 km.

Characteristics

The Mississippi gopher frog is a mid-sized, stocky, frog whose total body length is about 3 in (8 cm). The frog’s back ranges in color from black to brown or gray and is covered with dark spots and warts. The male's call has been compared to the sound of human snoring. Another notable feature of this secretive frog is, when exposed to bright light or threatened, the frog will put its hands in front of its face to shield its eyes. Other defense responses include inflating its body and secretion of a bitter, milky fluid from warty glands located on its back. Maximum longevity of the frog is six to 10 years.

The diets of adult frogs probably include frogs, toads, insects, spiders, and earthworms. Males reach sexual maturity at four to six months and females at two to three years. The fist-sized egg masses, containing 2,000 or more eggs, are typically attached to stems of emergent vegetation. Tadpoles average slightly over 1 in (3 cm) long and require 80 to 180 days to complete metamorphosis in the field.

The Mississippi Gopher Frog possesses several defense mechanisms in its immune system that are unique to Rana sevosa. The frog’s innate immune system is adept at recognizing outside prokaryotic pathogens. Rana sevosa reacts quickly to exterior pathogens, effectively limiting the extent of infections in the early hours after exposure. Similar to other species of frogs and toads, Rana Sevosa synthesizes antimicrobial peptides that act as effective defenses against outside pathogens. The frog secretes these chemicals through glands in its skin, and they are remarkably effective, killing certain pathogens in a matter of minutes.

Rana sevosa, similar to other species of frogs and toads, secrete antimicrobial peptides upon adrenergic stimulation, stress, and injury. Generally, in any sample collected there are multiple antimicrobial peptides released, each serving a different specific function. These antimicrobial peptides, noted for their concentrated effectiveness make for attractive models of bacteriostatic therapeutics. They also require no immunologic memory, they are secreted and effective against outside chemical threats as soon as they are released from the body of Rana sevosa. Furthermore, these antimicrobials only affect the membrane of the target pathogens as opposed to human anti-histamines that directly affect the human immune system.

Habitat

The Mississippi gopher frog’s habitat includes both upland, sandy areas covered with open longleaf pine forest with abundant ground cover; and isolated, temporary, wetland breeding sites within the forested landscape. Adult frogs spend most of their lives in or near underground refuges in uplands. They often use both active and abandoned gopher tortoise burrows; they also use abandoned mammal burrows, stump and root holes, and possibly crayfish burrows.

Breeding sites are isolated, grassy ponds that dry out completely at certain times of the year; their seasonal nature prevents establishment of a fish population, which would endanger tadpoles. Substantial winter rains are needed to ensure the ponds are filled sufficiently to allow development of juvenile frogs. The timing and frequency of rainfall is critical to the successful reproduction of the Mississippi gopher frog. Adults frogs move to breeding sites in association with heavy rains during winter and spring (December to April). Tadpoles must complete their metamorphosis before the ponds dry in the early summer.

Population/Reproduction

The Mississippi gopher frog was listed as endangered by the State of Mississippi in 1992 and by the US Fish and Wildlife Service in 2001. The only known remaining population of the Mississippi gopher frog consists of about 100 adult frogs from one site in Harrison County, Mississippi (Glen's Pond). Several possible sites are located in Jackson County, Mississippi. The Mississippi gopher frog is regarded as rarest amphibian in North America.

There were two known places of the Mississippi Gopher Frog. They were Glen’s Pond at Harrison County, Mississippi and Mikes Pond at Jackson County, Mississippi. Scientists discovered a population of Gopher Frogs at Mikes Pond in 2004. Now the only place you can find this species is at Glen’s Pond in Harrison County, Mississippi.

Population shifts in this species are mainly due to adult mortality, difference in ages at maturity, and a lack of adults returning to mate. Due to the facts that adults rarely return to reproduce and how isolated the population is, the population of this species of frog depends strongly on the constant return of frogs in their juvenile stage with the most consistent rate of reproduction a year. Male Mississippi Gopher frogs mature around the ages 6–8 months, while females mature around the ages of 24–36 months. Though anywhere from 65-92% of them survive to adulthood only a small percentage of them return to mate. Adult Mississippi Gopher Frogs live to about the age of 7 and are estimated to return and reproduce only once every 4–5 years.

Predation and disease

Adults face every-day threats from a wide assortment of possible predators, including birds, mammals, and reptiles. Tadpoles face predation from fish, aquatic insects, birds, turtles, and snakes. Chytridiomycosis caused by chytrid fungus, an infectious disease of amphibians, has had a detrimental effect on Mississippi gopher frog populations.

Threats

The historic regional decline of the species has been related to loss of open longleaf pine habitat needed for subsistence and the seasonal ponds needed for reproduction. Implementation of fire suppression in the 1930s was a factor, because frequent fires are necessary to maintain suitable open canopy and ground cover vegetation of the aquatic and terrestrial habitats. Reduced gopher tortoise populations may also be a factor of the frog's demise.

Other natural processes—such as genetic isolation, inbreeding, droughts, and floods—pose ongoing threats to the existing population. In addition, a host of immediate anthropogenic threats confront the only remaining breeding pond of the frog: a proposed residential development, new and expanded highways, and a proposed reservoir. The main threats posed by these projects are local changes in hydrology, the need for fire suppression, and habitat destruction and fragmentation. Other concerns include possible sedimentation and run-off of toxic chemicals that may injure or kill tadpoles and adult frogs.

This species of frog is quickly declining because of many reasons. One reason that might not be thought of as a main reason is genetic isolation. If these frogs are not all together in one general area they will not be able to reproduce. Since there is a lot of isolation of the Gopher Frog they cannot reproduce with other frogs, which makes the population smaller. If they do reproduce, it would be inbreeding which will lower the genetic variability of the frog. This could severely impact their chance of survival. This will all lead to the extinction of the Rana Sevosa if more conservation efforts are not being done.

A significant reason for under population in this species of frog has been threats toward the eggs. The estimated survival of Mississippi Gopher Frogs that live to reach the stage of metamorphosis is between 0-5.4%. Caddisfly larvae play a factor in causing egg mortality for these frogs and many other amphibians, but they are not found on the frog eggs after every mating season.

Some of the major threats to the Mississippi gopher frog includes the nearly complete destruction of the long-leaf pine forest which is a home to the frog. Other threats include fire suppression, drought, pesticides, urban sprawl, highway construction and the decline of gopher tortoises. Gopher tortoises build burrows in which the gopher frog and a variety of other animals take shelter, so a decline in gopher tortoises directly affects the habitats of gopher frogs in which they will be forced to relocate. The gopher frog is also threatened by chyridiomycosis which is a disease threatening amphibians worldwide. Furthermore, due to the small population of the gopher frog, they are highly susceptible to inbreeding which will decrease their genetic variability and can potentially decrease their chance for survival.

Recovery effort

The gopher frog is on the verge of extinction. Putting the frog on the endangered species list requires locals to receive a permit to kill or take one of the frogs from the wild; however, the species is so endangered that it would require an additional recovery plan in order to guide the species back to a healthy population level. Fortunately, a conservation team has been deployed in order to manage the recovery of the gopher frog by managing the habitat, supplementing habitat with sufficient water, raising tadpoles for release, constructing or restoring new breeding sites, and managing ecological requirements and diseases. Another recovery option available for the gopher frog is the introduction of more gopher tortoises for the gopher frogs in order to widen their habitats.

The Mississippi Gopher Frog is a very endangered species. The remaining population of these frogs is only at about one hundred adult frogs in Glen’s Pond at Harrison County, Mississippi. The Rana Sevosa is considered one of the rarest amphibians in North America. This shows that this species population is quickly declining. Conservation efforts are needed to keep this species of frog alive. Some ways to keep these Gopher frogs alive is by using well water to keep the soil waterlogged. This would increase the reproductive success of this species of frogs because they would have better environment for reproduction. This would hopefully end or slow down the extinction of the Rana Sevosa. Another conservation effort for these frogs would be to make sure the tadpoles are raised in a closed environment where they can develop fully and stay healthy. Many predators in ponds and in the wild endanger the tadpoles. If the tadpoles were raised in a safe environment they would survive and reproduce. This would help build the population of the Gopher Frog.

A Gopher Frog Recovery Team oversees conservation strategies that include pond water supplementation in dry years, habitat management, assisting tadpole survival, captive rearing, construction of alternative-breeding ponds, and treating infected tadpoles. This program needs to be continued and expanded. Surveys are needed to check the status of the recently discovered populations, and to determine whether or not the species survives elsewhere. The recovery effort was greatly enhanced in 2007 by the donation of "Mike's Pond" to the Nature Conversancy.

The US Fish and Wildlife Service has been working with the US Forest Service to protect the last remaining Mississippi gopher frog population. Both agencies have joined forces to rehabilitate a nearby pond as a future breeding site. The Fish and Wildlife Service, in conjunction with gopher frog researchers, has developed a strategy to introduce egg masses into this pond and to determine if the eggs can successfully develop into juvenile frogs at the site. Maintenance of open longleaf pine-dominated uplands and seasonal wetlands through growing season prescribed burning is the most appropriate form of management. This management strategy also favors gopher tortoises. Mechanical site preparation, as well as stump removal, should be avoided in forestry operations. Obviously, all known and potential breeding sites should be protected.

Five zoos (New Orleans, Memphis, Detroit, Miami, and Omaha) have 75 Mississippi gopher frogs in captivity, and are conducting ongoing artificial breeding programs.

Sources

• Goin, C.J. & M.G. Netting. 1940. A new gopher frog from the Gulf Coast with comments upon the Rana areolata group. Annals of the Carnegie Museum 28:137-169.
• RICHTER, S. C. and BROUGHTON, R. E. (2005), Development and characterization of polymorphic microsatellite DNA loci for the endangered dusky gopher frog, Rana sevosa, and two closely related species, Rana capito and Rana areolata. Molecular Ecology Notes, 5: 436–438. doi: 10.1111/j.1471-8286.2005.00954.x
• Ciaren Graham, Stephen C. Richter, Stephen McClean, Edmund O’Kane, Peter R. Flatt, Chris Shaw, Histamine-releasing and antimicrobial peptides from the skin secretions of the Dusky Gopher frog, Rana sevosa, Peptides, Volume 27, Issue 6, June 2006, Pages 1313-1319, ISSN 0196-9781, http://dx.doi.org/10.1016/j.peptides.2005.11.021.

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• Stephen C. Richter, Jeanne E. Young, Richard A. Seigel and Glen N. Johnson

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