Trachemys scripta

(Schoepff, 1792)
Common slider

Trachemys scripta is a medium to large (20-60 cm) turtle with a prominent patch (or patches) of red, orange, or yellow on each side of the head. Because there are several variable subspecies, the following description is highly generalized; see the Geographic Variation section for particulars of color and pattern.
The carapace is oval, weakly keeled, and has a slightly serrated posterior rim. Vertebral 1 is longer than broad or as long as broad; the other four are broader than long. The carapace is olive to brown with yellow markings varying geographically from stripes and bars to reticulations and ocelli. Markings on the marginal scutes also are variable but usually take the form of a dark blotch partly surrounded by a light band. Old males often become black. Bridge markings vary from dark blotches to bars. The hingeless plastron is yellow and exhibits a pattern that varies geographically from a single blotch on each scute (or rarely no pattern) to an extensive pattern covering most of the plastron. Its hindlobe is slightly notched posteriorly and the plastral formula is: abd > an > fem >< gul >< pect > hum. The head is moderate in size, with a protruding snout (more so in the males of some tropical subspecies) and a medially notched upper jaw. Skin is green to olive brown with yellow stripes. Supratemporal and orbitomandibular head stripes are conspicuous; a postorbital stripe of red, orange, or yellow is usually present; and a prefrontal arrow is formed as the supratemporal stripes pass forward from the eyes to meet a sagittal stripe on top of the snout. The neck is marked with numerous stripes and a central chin stripe runs backward and divides to form a Y-shaped mark. Limbs have numerous narrow stripes.
The diploid chromosome number is 50: 26 macrochromosomes and 24 microchromosomes (Killebrew, 1977a). Of these, 20 are metacentric and submetacentric, 10 are subtelocentric, and 20 are acrocentric and telocentric, with a total of 80 arms (Stock, 1972). DeSmet (1978) reported T. scripta to have 52 chromosomes (32 macrochromosomes and 20 microchromosomes).
Males are usually smaller than females and have long, thick tails, with the vent posterior to the carapacial rim. In some subspecies, males have elongated, curved foreclaws. Males often become melanistic with age (Lovich et al., 1990b; Tucker et al., 1995b).

In the United States, Trachemys scripta ranges from southeastern Virginia south to northern Florida and west to Kansas, Oklahoma, and New Mexico; thence it ranges through Mexico and Central America to northern Colombia and Venezuela. Due to its long popularity in the pet trade, T. s. elegans has been introduced worldwide.

Geographic Variation
Trachemys scripta is the most variable of all turtles; 15 subspecies have been described and named. The yellow-bellied slider T. scripta scripta (Schoepff, 1792), to 27 cm, ranges from southeastern Virginia to northern Florida. It has a wide yellow stripe on each pleural scute; a conspicuous yellow postorbital blotch, which may join a neck stripe; and a yellow plastron, which usually has ocelli or smudges only on the anteriormost scutes. The red-eared slider T. s. elegans (Wied-Neuweid, 1839), to 28 cm, occupies the Mississippi Valley from Illinois to the Gulf of Mexico. It has a wide red postorbital stripe, narrow chin stripes, a transverse yellow stripe on each pleural, and a plastral pattern of one large dark blotch or ocellus on each scute. The Cumberland slider T. s. troostii (Holbrook, 1836), to 21 cm, occurs in the upper parts of the Cumberland and Tennessee rivers, from southeastern Kentucky to northeastern Alabama. It has a narrow yellow postorbital stripe, broad chin stripes, a transverse yellow stripe on each pleural scute, and a plastral pattern of ocelli or small black smudges. The Nazas slider, T. s. hartwegi (Legler, 1990), to 29.8 cm, lives in the Rio Nazas drainage of Durango and Coahuila, Mexico, and is distinguished by having the interanal seam longer than the interabdominal seam. Each upper marginal bears a bold, dark-centered ocellus; other carapace pattern is indistinct. The orange postorbital stripe is large, nearly oval and separated from the orbit. The plastron pattern consists of small dark marks on the gular, humeral and pectoral scutes. This turtle closely resembles T. gaigeae, and may prove to be a subspecies of that species. The Cuatrocienegas slider T. s. taylori (Legler, 1960a), to 22 cm, only occurs in the Cuatro Ciénegas basin of Coahuila. It resembles T. s. elegans and has a supratemporal stripe which terminates abruptly on the neck behind an expanded, red, very elongated postorbital stripe; an extensive black plastral pattern with all parts interconnected; small, scattered, elongate or ovoid dark spots on the carapace; and the pectoral midseam longer than that of the gular. The Huastecan slider T. s. cataspila (Günther, 1885), to 22 cm, occurs on the Gulf Coastal Plain of Mexico from northern Tamaulipas to the vicinity of Punta del Morro, Veracruz. Its yellow supratemporal stripe is wide on the temples, and it has dark-centered ocelli on the pleurals and marginals and a medial plastral figure which does not extend along the interanal seam to the rear edge of the anals. The Meso-American slider T. s. venusta (Gray, 1856), to 48 cm, ranges from the city of Veracruz, Mexico, through Honduras (including the Yucatán Peninsula) in the Atlantic and Gulf drainages. The dark-centered ocelli on its pleural scutes are very large, its supratemporal stripe reaches the eye, and the seam-following plastral pattern is extensive. The Yaqui slider T. s. yaquia (Legler and Webb, 1970), to 31 cm, inhabits the lower parts of the Sonora, Yaqui, and Mayo drainages in Sonora, Mexico. Its postorbital mark is yellowish orange and only moderately expanded, the pleural scutes have only poorly defined ocelli with jagged black centers, and the medial plastral mark is extensive but faded in adults. The Fuerte slider T. s. hiltoni (Carr, 1942a), to 28 cm, is restricted to the Rio Fuerte drainage in Sonora and Sinaloa. Its orange postorbital part of the supratemporal stripe is either isolated anteriorly and posteriorly, or is connected posteriorly with a narrow orbital stripe; there are black smudgelike spots on the upper and lower surfaces of each lateral and posterior marginal scute and some pleural scutes; the plastron has a dark central blotch surrounding a narrow yellow medial area. The Baja California slider T. s. nebulosa (Van Denburgh, 1895), to 37 cm, occurs in freshwater bodies in southern Baja California. The orange or yellow supratemporal stripe does not reach the eye and ends as a large, oval postorbital spot well behind the eye; the carapace usually lacks ocelli, but may have a pattern of black spots and irregular light marks; the plastron bears a series of smudgelike medial blotches. The ornate slider T. s. ornata (Gray, 1831b), to 38 cm, occurs on the Pacific coastal plain of Mexico from northern Sinaloa to central Oaxaca and from Guatemala through Central America to Colombia. The orange postorbital stripe usually starts at the orbit, is expanded over the temple, and continues to the neck; the carapace has dark-centered ocelli on the pleurals; the plastral pattern consists of four concentric, faded medial lines which do not extend to the anal notch. Gray's slider T. s. grayi (Bocourt, 1868), to 60 cm, occurs from the Pacific coastal plain of Tehuantepec, Mexico, southeastward to La Libertad, El Salvador. The yellow supratemporal stripe reaches the eye; all head stripes are narrow; the carapace has dark-centered ocelli on the pleurals and marginals; and the plastral figure is diffused, fragmented, and faded in adults. The Colombian slider T. s. callirostris (Gray, 1856), to 25 cm, lives in the Caribbean drainages of Colombia and Venezuela. It is easily recognized by the large number of ocelli on the underside of the snout and on the upper and lower jaws; its broad, reddish, parallel-sided supratemporal stripe well-separated from the orbit; the pattern of ocelli on its carapace; and the extensive pattern of dark lines which cover most of its plastron. The Venezuelan slider T. s. chichiriviche (Pritchard and Trebbau, 1984), to 32.5 cm, inhabits the small coastal drainages between the Rio Tocuyo and Moron in northern Venezuela. This turtle also has ocelli on its chin, but has a brownish red, wedge-shaped supratemporal stripe well-separated from the orbit, oval or irregular black pleural blotches, and a narrow dark pattern along the plastral midseam. T. s. emolli (Legler, 1990), the Nicaraguan slider, to 37.2 cm, is found in the watersheds of Lakes Nicaragua and Managua, and in the Rio San Juan in Nicaragua and extreme northern Costa Rica. It has a broad, often bicolored, postorbital stripe which is constricted at the level of the tympanum. A large dark blotch is present on each pleural and marginal scute, and the vertebral keels are also dark. The adult plastron pattern consists only of dark seams. It is closely related to T. s. venusta.
In addition to subspecific variation, small populations of the same subspecies from separate but close locations often show much genetic variation, and this mtDNA variation may change over time (Scribner et al., 1995). It is possible that at least two or more species are involved in this variable complex (see courtship patterns below), and an extensive study of the relationships within this complex is sorely needed.

Although most freshwater habitats are occupied, Trachemys scripta prefers quiet waters with soft bottoms, an abundance of aquatic vegetation, and suitable basking sites. It is more riverine in the tropics.

Natural History
The timing and size of sexual maturity varies dramatically among and within populations. In males, maturity is evidenced by a combination of characters, not all of which may be present in a particular subspecies: elongation of the foreclaws. an increase in preanal tail length, and a significant reduction in the rate of growth. Populations from warm, nutrient rich habitats grow faster and mature earlier than do populations from colder, nutrient limited areas. Among North American subspecies, male T. s. elegans mature at 9.0-10.0 cm plastron length in 2-5 years, females at 15.0-19.5 cm plastron length in at least five years; male T. s. scripta mature at 10-12 cm in 4-5 years, and females at 16.0-23.2 cm in 5-8 years (Cagle, 1950; Webb, 1961; Gibbons and Greene, 1990; Mitchell and Pague, 1990). Male T. s. ornata in Panama mature at 12.5-13.5 cm and females at 24.0-26.0 (Moll and Legler, 1971). Size is a more important determinant of sexual maturity than age in males, but the reverse may be true in females. However, maturity in most organisms is not strictly size or age dependent but occurs at a point that minimizes a reduction in fitness caused by slower growth and smaller size.
The male and female reproductive cycles have been described by Moll and Legler (1971), Brewer and Killebrew (1986), and Sprando and Russell (1988). The stages are essentially the same in turtles from North America and Panama, but the timing is somewhat different. Spermatogenesis begins in May with proliferation of spermatogonia and the presence of Sertoli nuclei on or near the basement membrane of the seminiferous tubules. Spermatogonia become more prevalent in late May, and increasing numbers of spermatocytes appear in June. Spermatocytogenesis begins in mid-June and continues through early September, peaking in mid-July into early August. Numerous spermatocytes and spermatids are present in the tubules by mid-July, and some males show differentiation of spermatids into mature spermatozoa. Spermiogenesis increases through August, and spermatozoa are clumped in bunches at the distal ends of Sertoli cells. Spermiogenesis slows by late September and ends in mid-November. Spermiation begins in early to mid-September, peaks in October, and gradually declines until the end of November. In Panama the cycle appears to be completed in small males early in November, but it continues into December in larger males. In North America, a period of winter quiescence in spermatogenic activity occurs; in Panama, the quiescent period corresponds to the dry season from January to May. Epididymides are packed with mature sperm throughout the year. Mean testis weight is lowest in May, highest in August.
The ovarian cycle involves four phases: 1) The follicular enlargement phase begins in August or September and continues through November as follicles add yolk through vitellogenesis. Ovulatory size is reached in late November or December, and ovarian weight is greatest from early January to May. 2) The ovulation and intrauterine phase begins in April in Panamanian females and May in those from North America, and extends through June, 3) The oviposition phase is April-May in Panama and May-early July in North America (there is overlap between phases 2 and 3 in females that lay multiple clutches). 4) The quiescence period occurs between the last oviposition and the beginning of the next follicular enlargement phase in August (in North American females, quiescence also occurs during winter hibernation).
Courtship and mating occur in both the spring and fall. Two courtship patterns exist (Ernst and Barbour, 1989; Lovich et al., 1991b; Seidel and Fritz, 1997), depending on whether or not the males possess elongated foreclaws. If elongated foreclaws are present, such as in subspecies like T. s. elegans, the male swims to a position in front of the female, turns to face her, extends his forelegs with palms outward, and strokes her face with his foreclaws (Jackson and Davis, 1972). If the male lacks elongated foreclaws, such as in subspecies like T. s. taylori, he does not swim in front of the female, but instead pursues her and vigorously bites the posterior rim of her shell, hindlegs, and tail (Davis and Jackson, 1973). In both cases, after the female has been subdued, the male mounts from the rear, and the couple sinks to the bottom to copulate. Sperm may be stored by the female for as long as 79 days (Gist and Jones, 1987, 1989).
Nesting in the more temperate zones occurs from April to July but may occur during the dry season (December-May) in tropical subspecies. The nest is usually excavated on the shore of a fresh waterbody, but some T. s. venusta in Costa Rica nest on Caribbean sea beaches (Moll, 1994). Nests are usually flask shaped. The nest is excavated by the female with alternate scoops of her hind legs. If the ground is too hard, she may release fluid from her cloacal bladders to soften it. Once the initial entrance to the nest is excavated to a depth of 2.5-10.0 cm the female uses their hind feet to enlarge the nest chamber as much as 11.0-20.5 cm deep. Although nesting in North America is usually singularly, tropical females often nest communally (Moll and Moll, 1990).
As many as five clutches may be deposited a year in North America, and up to six in the Neotropics. Clutch interval is 12-36 days. Clutches contain 2-30 eggs (Moll and Moll, 1990; Ernst et al., 1994; Tucker, 1996), and clutch size is positively correlated with female body size. The ovoid eggs of sliders north of Mexico are 30.9-43.0 mm x 19.4-25.6 mm (Ernst et al., 1994); those of Central American sliders are slightly more elongate, 27.0-47.6 x 16.0-31.3 mm (Moll and Legler, 1971; Moll and Moll, 1990). Incubation, depending on thermal conditions, may take 59-112 days. In North America the young hatch and emerge in late summer or early fall, although some may overwinter in the nest. In the Costa Rica, hatchlings emerge in May and June (Moll, 1994).
North American hatchlings have carapaces 25.4-35.8 mm long; Central American hatchlings may be 36.0-41.8 mm (Moll, 1994). The carapace is green with yellow markings, there are smudges or ocelli on the underside of the marginals, and the bridge and plastron are brightly patterned.
The food preferences of Trachemys scripta change with age: juveniles are highly carnivorous, but as they become older they eat progressively larger quantities of vegetable matter (Clark and Gibbons, 1969; Hart, 1983; Parmenter and Avery, 1990). Adults are omnivorous and exhibit no obvious preference for either animal or plant food; they will take almost any food item available. Foods recorded from T. scripta include algae, duckweed, and assorted emergent herbaceous plants; animals include sponges, snails, clams, bryozoans, cladocerans, ostracods, isopods, amphipods, crayfish, shrimp, spiders, insects (adults and larvae), fish, frogs (eggs, tadpoles, adults), turtle scutes, water snakes (Nerodia), and waterfowl (Parmenter and Avery, 1990). Carrion is sometimes eaten (Carl H. Ernst, pers. obs.). Captives readily take commercial trout chow, fresh and canned fish, raw beef and chicken, canned dog food, earthworms, newborn mice, bananas, watermelon, cantalope, romaine lettuce, and various other green vegetables.
Sliders are quite fond of basking, and may pile up several deep at preferred sites.

IUCN Red List Status (1996)
Lower risk: near threatened.