(Agassiz, 1857)
Texas tortoise
Recognition
The oblong carapace (to 24.0 cm) is rather flat topped, highest behind the center, and drops off abruptly to a serrated rear margin. The cervical scute is about as broad as long, but may be absent. Vertebrals are broader than long; the 1st is usually narrowest, and the 3rd broadest. The carapace has a somewhat rough, ridged appearance, caused by well-marked growth annuli surrounding the slightly raised vertebral and pleural areolae. There are usually 11 marginals on each side, and the single supracaudal scute is undivided and downturned. The carapace is brown, and the areolae may be yellow. The yellow plastron is large and well-developed with the paired gular scutes elongated, somewhat forked, and extending anteriorly (and sometimes upward) beyond the carapacial rim. Its forelobe is longer than and as broad as, or slightly narrower than, the hindlobe, which has a deep posterior notch. The plastral formula is: abd > hum > gul > fem > an >< pect. The bridge is broad, usually with two axillary scutes. The head is wedge shaped with a somewhat pointed, nonprojecting snout and a slightly hooked upper jaw. The angle between the upper triturating ridges is usually more than 65° but less than 70°. Dorsal head scales are large and irregularly shaped. Well-developed glands beneath the rami of the lower jaw become prominent in males during the mating season. Head, limbs, and tail are yellowish brown. Anterior foreleg surfaces are covered with large, slightly overlapping scales in seven or eight longitudinal rows. The thighs contain a series of small conical tubercles.
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).
The males have slightly longer and narrower carapaces, a longer and more deeply forked gular projection, a concave plastron, and better developed chin glands.
Distribution
According to Rose and Judd (1989), Gopherus berlandieri occurs in Texas from Val Verde County eastward across the state through Kinney, Uvalde, Bandera, Bexar, Guadalupe, La Vaca, Jackson, and Matagorda counties. There are reports from Sutton, Fort Bend, and Galveston counties, but these probably represent released animals, and a Brewster County record is probably incorrect. In northern Mexico, it ranges over most of Tamaulipas, northeastern San Luis Potosi, the northern and eastern portions of Nuevo Leon, and in Coahuila from Monclova north through Nuevo Rosita to Ciudad Acuna (Rose and Judd, 1989). Nowhere within its range do its densities appear high, and populations are disjunct.
Geographic Variation
No subspecies have been described, but populations differ in male carapace length (Rose and Judd, 1989).
Habitat
This species is found in habitats ranging from near-desert in Mexico to scrub forests in humid and subtropical parts of southern Texas. Sandy, well-drained soils are preferred, and open scrub woods seem to be specially favored. In southern Texas the species occurs from sea level to 100 or 200 m; in Tamaulipas it ranges up to 884 m.
Natural History
Auffenberg and Weaver (1969) found that secondary sex characters are clearly evident only in tortoises larger than 10.5 cm in carapace length, but Judd and Rose (1989) reported that sexually dimorphic characters were not evident in tortoises less than 12.5 cm long. Sexual maturity is apparently attained at a carapace length of 12.5 cm or more when the animal is 3-5 years old. Females 14.5-15.0 cm examined by Rose and Judd (1982) were immature, but those 15.5-16.5 cm long contained shelled oviductal eggs. Judd and Rose (1989) reported a female 14.0 cm with eggs, and Germano (1994) thought that females do not reproduce until 11-17 years old. The annual reproductive cycles of neither sex have been described.
The courtship and mating season in Texas extends from June to September, but most copulations occur in late summer, and captive males have initiated courtship as early as May (Rose and Judd, 1989). During this period the males are quite belligerent towards each other. According to Weaver (1970), the male trails the female during courtship, bobbing his head in her direction. When she is caught, he attempts to confront her, face to face. He stops her by biting her head, forefeet, and anterior carapace, and ramming her with his gular projection. She usually pivots to avoid this, but he moves with her. When she stops pivoting and withdraws her head, he continues to push her around. Finally he works around to the rear of her carapace and mounts, with his forefeet on the dorsal surface of her carapace and his hind feet firmly planted on the ground. Intromission follows.
Nesting is known to occur from April into July, but the primary months in Texas are May and June. Females have, however, been found to contain shelled oviductal eggs in November. The nest is usually merely a concavity that has been softened with bladder water.
One to two clutches of 1-5 (Judd and Rose, 1989, reported clutches of 7 and 10 eggs), but usually 2-3 eggs, are laid per year. These eggs are distributed in multiple nests over a period of time (Rose and Judd, 1989), and not all females reproduce each year. The eggs are white, oval to elongated (40.0-53.7 x 29.0-34.1 mm), and pliable when laid, but the shell hardens quickly to an almost porcelain-like appearance (Rose and Judd, 1989). If the shell was hard when oviposited, the egg could hardly pass through the narrow plastral opening (Rose and Judd, 1991). To aid in egg-laying, the pelvic girdle opening is enlarged (Long and Rose, 1989). The xiphiplastra and not sutured to the hypoplastra (except in extreme lateral aspect), and the ziphiplastral-hypoplastral connections serve as hinges to lower the xiphiplastra during oviposition, while the posterior carapace is forced upward (Rose and Judd, 1991). Incubation lasts 88-118 days (Judd and McQueen, 1980). Hatchlings are about 40-50 mm in both length and width; their shells are brown and cream in color.
The primary diet is low grasses and herbs (violets, asters), but the red fruits, flowers and stems of Opuntia cacti are often eaten, and insects, snails, faecal matter, and bleached animal bones are also consumed (Rose and Judd, 1982; Ernst et al., 1994). Captives eat romaine lettuce, tomatoes, shaved carrots, grass, clover, apples, and bananas; some captives occasionally eat raw meat.
Unlike the other species of Gopherus in the United States, G. berlandieri usually does not dig an extensive burrow; tunnels are seldom over 40 cm in length. Instead, it uses its gular projection, forelimbs, and the lateral edges of the shell to push away the surface debris and soil to create a resting place, to which it often returns. This so-called pallet usually is located under a bush or the edge of a clump of cactus and is simply a ramp sloping just steeply enough to accommodate the anterior edge of the shell below the surface. There are usually several pallets within a tortoise's home range. Continued use of a pallet, together with the clearing away of accumulated soil and debris, tends to deepen it; the deepest one found by Auffenberg and Weaver (1969) was 1.5 m deep at its anterior end and 5 m long. They also found that pallet use is seasonal. Pallets in thick brush near Brownsville, Texas, are used throughout the year, but in summer proportionately more tortoises are found in pallets in such places. In winter a greater proportion of tortoises are found in pallets in open brush or in grassland. Texas tortoises also sometimes occupy empty mammal burrows of suitable size, and on occasion further excavate these.
IUCN Red List Status (1996)
Not listed. The Texas tortoise is declining in areas of extensive agriculture, particularly in the Rio Grande Valley, where 90% of its natural brush habitat has been eliminated since the 1930s, and 80% of the remaining brushland is unprotected and threatened by development (Rameriz, in Rose and Judd, 1989). Few are eaten, but many are killed on the roads each year. In the past, many Texas tortoises were sold in the pet trade, but the animal has been protected in Texas since 1967.