Gopherus polyphemus


Image from Ashton and Ashton, 1992
Gopher Tortoise Taxonomic History
Species Description
Biogeography
Reproductive Behavior
Feeding and Diet
Lifestyle
Conservation
Museums
Links
Bibliography

Image from pelotes.jea.com




Taxonomic History

The gopher tortoise, Gopherus polyphemus was named by F.M. Daudin in 1802 and appeared in "Historie naturelle generale et particuliere, des Reptiles" It was originally named Testudo polyphemus by Daudin, and described to be located in the vicinity of Savannah, Georgia, but the type is not designated. The name Gopherus polyphemus was first used by Leonhard Stejneger in 1893. The holotype for the species with an unknown collector is at the Florida Geological Survey. (Auffenberg and Franz, 1978)

Taxonomic Hierarchy

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Testudines
Family: Testudinidae
Genus: Gopherus
Species: Gopherus polyphemus

Taxonomic Hierarchy from Integrated Taxonomic Information System



Species Description

Gopherus polyphemus characteristic features include (Ernst et al., 1994):


Image from Ashton and Ashton, 1992

G. polyphemus also exhibits sexual dimorphic characteristics (McRae, 1981a):

Biogeography

The range of G. polyphemus extends from extreme South Carolina throughout Florida, southern regions of Georgia, Alabama, Mississipi to southeast Louisianna

There are no known subspecies of G. polyphemus but it has been observed that examples in the west end of the range are lighter in color. (Ernst et al., 1994)


Map from Ernst et al., 1994

Reproductive Behavior

G. polyphemus are slow to mature and do not begin to reach reproductive age until they are approximately 10 years old. Eggs are layed in small clutches of approximately 8 eggs and are extremely susceptable to predators, such as Mephitis mephitis (striped skunk) and Dosypus novemcinctus (armadillo). 90% of clutches may be destroyed before the end of the incubation period, and less than 6% of eggs layed are expected to survive from the time they are layed to reaching 1 yr. old. (Alderton, 1998)

The courtship ritual of G. polyphemus is characterized by the male walking in a circle in front of a female and periodically stopping to bob his head up and down to attract the attention of the female. When the female approaches the male he will violently bob his head up and down. As the female approaches closer, he wil bite her on the foreleg, head, and anterior edge of her carapace and gular projection. In response the female will back up and turn in a semicircle, stop, and then strech her hind legs out. The female will pivot 180º so her posterior is near the males head in an act of presentation. The male will then attempt to mount the female, and if successful, will extend the neck and head with mouth wide open, while stroking or tapping the females carapace with his foreclaw. (Description of courtship ritual from Auffenberg and Franz, 1966)


Image from Auffenberg and Franz, 1966
Images show (A) Male bobbing head in front of female (B) male biting gular of female (C) Biting continues and female streches hind legs (D) Male mounts female

The major reproductive season for G. polyphemus occurs during the spring, and it has been found that the chin glands become swollen during the breeding season. The scent emitted from these glands are transmitted from the chin to a slightly enlarged scale near the elbow by rubbing the gland on the forelimbs. The bobbing of the head in the male may help transfer this scent to the females as a way to attract mates.(Auffenberg in Ernst, 474) Another interesting fact is that although there are no strong pair bonds, male gopher tortoises are known to visit specific females within their range to mate with. (Alderton, 1998)

Eggs are deposited by the female in late April-mid July into nests that can be away from the burrow or directly at the entrance of the burrow. Eggs hatch and emerge around August to October. Hatchlings have nearly round carapaces which are slightly longer than wide. Dorsal scutes have a yellow colored center with deep brown/grey coloration on the edges of scutes and on marginal scutes. (Ernst et al., 1994) Hatchlings stay near the nest (approximately within 15m of the nest) for their first year of life, and then disperse to the periphery of the colony as a result of competition from adult tortoises. (McRae, 1981)

Feeding and Diet

Gopherus polyphemus is known to feed on a large variety of plants and vegetation, such as grasses, legumes, and leaves. Macdonald and Mushinsky studied scat and observed feeding behavior and found grasses, such as Andropogon, Dichanthelium, Paspalum, and Aristida to make up about a third of the adult diet. Species from the following genera: Pityopsis, the silkgrass (a grasslike aster); Galactia, the milkpea; and leaves from Pinus and Quercus, the pine and oak trees, were also found to be major components of diet. Grasses and legumes are readily available to the gopher tortoise, but the leaves from Pinusand Quercus are available mainly as seedlings or dead material fallen from the trees. In addition, gopher tortoises eat flowers from the Cnidoscolus, Tillandsia, Richardia, and Dyschoriste. Juvinile gopher tortoises have similar diets to adults, although Aristida is too tough and fibrous for the young digestive system. Juviniles also consume more legumes and less grasses than adults, which gives them more protein essential for development. (Macdonald and Mushinsky, 1988)

Lifestyle


Image from www.pfmt.org

G. polyphemus seeks environments where the soil tends to be dry and where there is a diversity of vegetation. (Diemer, 1986) Gopher tortoises can be found in longleaf pine and oak uplands; xeric hammock-sand pine, oak ridges/beach scrub; and ruderial regions, such as roadsides, along fences, clearings, and old fields. (Auffenberg and Franz, 1982) Gopher tortoise burrows help in protecting the tortoise from variable temperature conditions for effective thermoregulation, and predators. (Diemer, 1986)

G. polyphemus is active during every month of the year. The most activity occurs during May-August and G. polyphemus is least active from December-February. Activity in winter months usually only occurs when temperatures rise above 21ºC G. polyphemus is strictly diurnal, and throughout the year activity peaks during the hottest hours of the afternoon between 1:00 and 4:00, but in warmer months, activity extends over a longer period from 7:00 am to 8:00 pm, and on a warm winter day, activity is restricted to the afternoon when it is the warmest. (Douglas, 1978) For feeding, gopher tortoises will stay approximately within 30 m of its burrow, showing the dependence on the burrow as a form of escape from predators and extreme temperatures. (McRae et al, 1981) However, for mating purposes, males are known to travel long distances, up to 7.7 km (McRae, 1981), to mate with females. When body temperature rises, G. polyphemus will seek shade, froth at the mouth and breath rapidly. Frothing at the mouth occurs especially when temperatures rise above 38ºC. When frothing occurs it is usually accompanied by the repeated extention and retraction of the head to spread saliva over the neck and aid in evaporative cooling. The average body temperature was found to be approximately 34.7ºc in one study, showing that G. polyphemus can withstand high temperatures. G. polyphemus can also be found basking with the neck, limbs, and carapace exposed sitting on a mound or burrow entrance (Douglas, 1978)

Conservation

G. polyphemus is listed as a "threatened" species on the Endangered Species List, and was listed on July 7, 1987. Most of the decline in population is due to human population growth and destruction of natural habitat. Agriculture, industry, tourism and residential development have destroyed much of the land necessary for the gopher tortoise. Preventing tortoises from gaining food sources, a lack of shade, and the threat of being run over by motor vehicles. Under the Endangered Species Act, it is illegal to collect or hunt G. polyphemus in Florida, Alabama, or South Carolina. Currently, parts of gopher tortoise habitat are being preserved and maintained by burning down areas of forest to provide an open habitat for the tortoise (Beacham, et al, 2001) One study found that the effects of habitat destruction, degredation, and human predation reduced the gopher tortoise population by 80% in the past 100 years. (Auffenberg and Franz, 1982) It has also been found that clearing of natural habitat for agricultural purposes has harmed populations, and has especially been a problem in Florida where much sandhill habitat has been cleared for citrus groves. Farmers also consider the gopher tortise a pest and have them removed from their natural habitat. (Auffenberg and Franz, 1982)

Another source of population decline in gopher tortoise populations has been the outbreak of Upper Respiratory Tract Disease, a disorder originally discovered in Gopherus agassizii, the desert tortoise, which causes nasal passages to become filled with mucous,lethargy, and loss of appetite. (Jacobson et al. 1991) It is caused by Mycoplasma agassizii, a bacterium which colonizes the respiratory tract. (Brown et al. 1998) Much research is being conducted to try to better understand the spread and nature of the disease. A recent study (Smith et al. 1998) showed that URTD is found more often in males than in females, which is believed to be a result of males having a larger home range size due to the greater distances they travel to mate (McRae et al. 1981), thus giving them a greater probability of coming into contact with infected individuals. A great concern in the conservation of the gopher tortoise is the fear that infected tortoises that are found areas of urban and agricultural development are being relocated to designated protected areas, where they have the potential of infecting these populations. (Smith et al. 1998)

Museums and Collections with G. polyphemus