(Daudin, 1802)
Gopher tortoise
Recognition
The oblong carapace (to 38.7 cm) is flat topped with abruptly descending sides, and lacks a cervical indentation. It is usually widest in front of the bridge, highest in the sacral region, and may be somewhat constricted behind the bridge. It drops off abruptly to the rear, and the posterior marginals are only slightly serrated. The cervical scute is about as broad as long. Vertebrals are broader than long; the 1st is usually the narrowest, the 3rd broadest, and the 5th laterally expanded. Well-defined growth annuli occur on young tortoises, but the carapace becomes smoother with age. There are usually 11 marginals on each side, and the single supracaudal scute is undivided and downturned. The carapace is dark brown to grayish black; some individuals have lighter vertebral and pleural areolae. The yellow to gray plastron is well-developed and covers much of the carapacial opening. Its forelobe is longer and slightly narrower than the hindlobe, which bears a well-defined posterior notch. The plastral formula is: abd > hum > gul >< fem > pect >< an. The paired gular scutes are thickened, project beyond the carapacial rim (especially in males), and may be upturned. The head is broad to moderate with a nonprojecting snout, and the upper jaws are neither notched nor hooked. The scales on the top of the head are small and irregular; the prefrontal scale is divided longitudinally, and there is a small single frontal. The iris is dark brown. Head, limbs, and tail are grayish black; limb sockets are yellow. The foreleg's anterior surface is covered with large, non- or slightly overlapping scales in seven or eight longitudinal rows. The hindlimbs appear small.
Diploid chromosomes number 52 (26 macrochromosomes and 26 microchromosomes): 20 metacentric and submetacentric, 10 subtelocentric, and 22 acrocentric and telocentric (Stock, 1972; Dowler and Bickham, 1982).
Males have more concave plastra and larger integumentary glands under the chin than females have.
Distribution
Gopherus polyphemus ranges from extreme southwestern South Carolina south along the Atlantic Coastal Plain through Florida, and west along the Gulf Coastal Plain to southeastern Louisiana.
Habitat
Gopher tortoises usually live on well-drained, sandy soils in contiguous areas situated in pine-oak, beach scrub, oak hammocks pine flatwoods, or saw palmetto. Tortoise densities and movements are both directly related to herbaceous biomass, and densities are highest in fire-adapted plant associations and disturbed areas, such as roadsides, fence-rows, old fields, berms, and the edges of plantations (Auffenberg and Franz, 1982; Diemer, 1986, 1989; Breininger et al., 1994). Adequate herbaceous foods and sunny nesting sites must be present.
Natural History
In Georgia, males mature in 16-18 years at carapace lengths of 23-24 cm (Landers et al., 1980); in Florida they may mature in 9-18 years at 17.7-23.0 cm (Diemer and Moore, 1994; Mushinsky et al., 1994). Sexual maturity in female gopher tortoises is reached in 9-21 years at carapace lengths of 21.0-28.2 cm (Iverson, 1980a; Landers et al., 1980, 1982; Diemer, 1986, 1989; Smith, 1992; Diemer and Moore, 1994; Mushinsky et al., 1994).
The male reproductive cycle has not been described. In females a period of ovarian regression occurs in summer following oviposition (Iverson, 1980a). Vitellogenesis resumes in September, and follicles continue to enlarge until ovulation in April or May, although yolking may be slowed during the winter. Oviducal eggs have been found as early as late April, and mature females may contain shelled eggs from mid-May to mid-June (Diemer and Moore, 1994). Sperm has been found within the oviductal lumen and endometrial glands from the posterior tube to the anterior uterus throughout the reproductive cycle, indicating that females may store sperm for later use (Palmer and Guillette, 1988, 1990; Gist and Jones, 1989).
Courtship occurs principally in the spring, with mating in April and May; however, fall courtships do occur. Courtship apparently consists of several basic sequential activities. The first of these Auffenberg (1966b) termed the "male orientation circle": the male walks in a circle and periodically stops and bobs his head, perhaps to attract the attention of a sexually responsive female. When a female approaches he bobs his head violently, then bites her on the forelegs, head, anterior edge of the carapace, and especially the gular projection. (This is probably the method of sex identification; females do not bite one another or males). The female then backs in a semicircle, stops, and stretches her hindlegs. Later she pivots 180°, so that the posterior part of her shell is nearest the male's head; this may be a primitive form of presentation. The male's attempts to mount—usually unsuccessful—are followed by more biting, which in turn is followed by a successful mounting and coition. Auffenberg (1969) found that in some instances, just before the male's behavior changed from head bobbing to biting, the female rubbed the side of her face and chin across her outstretched front legs. Both adult males and females of Gopherus have a pair of glands on the chin; although small most of the year, these glands usually become swollen in the breeding season. Both sexes have an enlarged scale, more prominent than the rest, on each front leg near the elbow. Scent probably is transferred by the female from her chin to her front legs by means of this scale. Her chin rubbing seems to be a response to the male's head bobbing, and Auffenberg speculated that this action causes the male to change his behavior from bobbing to biting. His bobbing may provide the female with more than just a visual cue: he has glands beneath the lower jawbone, and the bobbing may also serve to spread a scent to signal the female.
Oviposition may take place any time from late April to mid-July, but most nesting occurs from mid-May to mid-June. Some nests are located at a considerable distance from the burrow, but many are dug in the soil of the burrow apron. Pocket gopher (Geomys pinetis) mounds are also sometimes used for nest sites (Epperson and Wendland, 1997).
Nests extend to a depth of about 15 cm, and 1-25 eggs (usually 5-9) eggs are laid in the single, annual clutch (Iverson, 1980a; Smith, 1992; Diemer and Moore, 1994; Germano, 1994). Clutch size is directly correlated to female body size (Landers et al., 1980; Smith, 1992; Diemer and Moore, 1994). The white eggs are brittle shelled and almost spherical (diameter 37.9-53.2 mm, but usually 41-43 mm). Hatching and emergence occur from August to October; natural incubation probably lasts 80-90 days in Florida (Iverson, 1980a) and 97-106 days in Georgia (Landers et al., 1980), and up to 110 days in South Carolina (Wright, 1982).
Hatchlings have rounded 32.0-51.8 mm carapaces. At hatching, the yolk sac is large, averaging 10 x 10 x 5 mm, but it is completely resorbed within 18-24 hours.
Natural foods include large amounts of grasses and leaves, with occasional bits of hard fruits, bones, charcoal, and insects (Carr, 1952; Diemer, 1989). In Florida, MacDonald and Mushinsky (1988) found the following families the most frequent components of the diet: Poaceae (Aristida, 98% of scats), Asteraceae (60% of scats), Pinaceae (84%), and Fagaceae (79%). Sixty-eight genera from 26 families were identified in the diet. Other than Aristida and Pinus, the genera of other commonly eaten plants were Cnidoscolus, Galactia, Pityopsis, Quercus, Richardia, and Tillandsia. Some scats also contained insects and charcoal. Captives eat lettuce, grasses, dandelions, various fruits, and occasionally hamburger and canned dog food.
Where the soil is deep enough, G. polyphemus digs a long, straight, unbranched burrow 2.7-6.1 m (average 4.5 m) long and 1.4-2.8 m deep (Hansen, 1963; Diemer, 1989). There usually is an enlarged chamber at the end of the tunnel, where the tortoise sleeps, turns around, aestivates in the summer, and hibernates in the winter. A continuous cycle of burrow creation and abandonment occurs throughout the year and the life of a tortoise. Even juveniles dig burrows, in which they spend about 90% of the time (Wilson et al., 1994).
IUCN Red List Status (1996)
Vulnerable (A1acde). Unfortunately, good natural habitats for gopher tortoises are rapidly disappearing throughout its range. It is now legally protected as either endangered or threatened in most states where it lives, and is federally listed under the Endangered Species Act as threatened in Louisiana, Mississippi, and western Alabama. It is listed on Appendix II of CITES.