Lovich and McCoy, 1992
Escambia map turtle
Graptemys ernsti is a moderate-sized (carapace length to 28.5 cm in females) high-domed, medially keeled map turtle with a single yellow bar on the dorsal surface of each marginal scute. Dark smudges lie between the marginals at the rim of the carapace. The vertebral keel is composed of laterally compressed knobs that are most prominent on the posterior parts of the second and third vertebrals. A pronounced, broken, black stripe runs down the center of the olive carapace. Relatively wide yellow rings and vermiculations are present on the distal parts of the pleural scutes. The hingeless, pale-yellow plastron has a dark seam-following pattern, especially along seams running perpendicular to the long axis of the body. The ventral surface of each marginal scute has a dark, wide, diffuse border, which forms one or two semicircles on some scutes. The brown to olive skin is broken with light-yellow or yellowish green stripes and blotches. The head has a large interorbital blotch that is not connected to the large postorbital blotches on each side of the head. A distinct three-pronged mark is present on the anterior part of the interorbital blotch. A pair of supraoccipital spots commonly lie between the posterior extensions of the postorbital blotches, and may fuse to the first paramedial neck stripes. Dorsal neck stripes are relatively thick and, commonly, roughly equal in size, but some stripes may be thin. Some individuals have a light blotch beneath each eye.
McKown (1972) reported that Graptemys pulchra (sensu lato) has a diploid chromosome number of 52 including 26 macrochromosomes with 48 arms and 26 microchromosomes with 26 arms.
Adult females are more than twice the size of adult males, and have conspicuously enlarged heads with broad crushing jaw surfaces. Large females appear hump-backed owing to a dramatic incline of the first vertebral scute. Males have longer tails with the vent posterior to the rim of the carapace. Both sexes have relatively flat plastra.
Graptemys ernsti is restricted to rivers flowing into Pensacola Bay, including the following in Alabama and Florida: Yellow River, Escambia River, Conecuh River, and Shoal River.
No subspecies are recognized. This species was formerly considered only a variant of Graptemys pulchra. Lovich and McCoy (1992) demonstrated that G. pulchra (sensu lato) is actually composed of three distinct species.
The Escambia map turtle is found in relatively large, swift creeks and rivers, with sandy or gravelly bottoms. Stream sections with an abundance of basking sites in the form of snags, logs, and brush are preferred.
Shealy (1976) provided detailed information on the reproductive ecology of G. ernsti in the Conecuh River of Alabama. Males mature three or four years after hatching at a minimum carapace length of 80 mm. Females are judged to be sexually mature if corpora lutea or ovarian follicles larger than 15 mm in diameter are present. Based on this criteria, females mature in about 14 years at a carapace length of 22 cm. The largest immature female in the population studied by Shealy (1976) was 22 cm, and the smallest mature female was 21.2 cm. Active sperm are present in the epididymides of mature males throughout the year. Shealy (1976) thought this indicated that mating could occur at any time of the year, but mating activity has only been observed from September to November. Testis diameter is greatest in September, a time when follicular development is most rapid in females. The percentage of follicles larger than 10 mm in diameter, relative to the maximum number of eggs produced in a season, decreases from May to September. Ovulation begins in late April and continues through July. Shealy (1976) suggested that some follicles are not ovulated during the normal nesting season. Atretic follicles account for no more than 5% of the reproductive potential, leading Shealy to suggest that some follicles are ovulated after the normal nesting season or held over to the following year. The number of follicles larger than 10 mm in diameter and the number of eggs produced are positively correlated with female carapace length. The number of large ovarian follicles produced in a season ranges from 7 to 71 (mean = 29). Almost all follicles larger than 10 mm are ovulated. As the mean number of ovulatory follicles in a given season is 29 and the mean clutch size is 7.2 eggs, then the mean estimated number of clutches per season is four. The number of clutches laid per season is also correlated with female size. Data based on autopsies and nesting signs suggest that large females ovulate earlier and later in the nesting season than smaller females. In addition, one or two clutches per season is typical of small females in their first reproductive season, but the largest females may produce six or seven clutches per season.
Courtship starts with the male approaching the cloacal region of the female with his neck outstretched. He then swims in front of the female assuming one of three positions face-to-face: slightly to either side, slightly above, or slightly below her head. Next he begins to rapidly vibrate his head vertically against the side of the female's snout, alternating sides at intervals of approximately 15 seconds. During this action the female withdraws her head somewhat and Partially closes her eyes. following head bobbing, the male swims to the rear of the female and attempts to copulate by looping his tail beneath hers in an effort to arroyo the cloacae. This sequence is often repeated several times before successful copulation. Oviducal scrapings in March and May contain active sperm, demonstrating the potential for sperm storage.
The nesting season lasts from late April to late July. Most nests are dug in large sandbars located at sharp bends in rivers. Most are excavated in very fine sand at elevations 2-3 m above the existing water level, and 3-15 m from the water's edge. Nesting may occur at any time of day. Females intent on oviposition appear to move onto shore very cautiously, pausing occasionally to press their noses to the substrate as if searching for olfactory cues. Possible additional substrate-testing behavior includes sweeping the sand with the front legs to form furrows 1-5 cm deep, and digging test holes with the hindlegs. Such holes often have stones, leaf litter, roots, or other potential obstacles at the bottom. The actual nest cavity is constructed with alternating sweeps and scrapes of the hindlegs. It is flask shaped, about 15 cm deep, with a lower spherical chamber diameter of about 10 cm, and a neck diameter of about 4 cm. After depositing the eggs the female packs the nest with sand and smooths the area over the nest entrance with lateral movements of her body before crawling directly back to water.
Oviducal eggs have mean dimensions of 38 x 26 mm, and eggs from nests have mean dimensions of 38 x 27 mm; the slight difference is due to rapid water absorption. During incubation the eggs assume an almost spherical shape. Eggs incubated under artificial conditions closely approximating those of natural nests hatch in 74-79 days (X = 76) (Shealy, 1976). Nest temperatures of natural nests range from 23 to 31°C (mean 29). Nests may be submerged by high water for up to a week or more and still produce hatchlings. Nine of 64 eggs collected in the field and incubated under artificial conditions by Shealy were infertile. Eggs from one fertile clutch had mean dimensions of 29.5 x 43 mm just prior to hatching.
Hatchlings pierce the apex of the eggshell and then remain in the shell for about four days while the yolk is absorbed. The yolk sac is 12-15 mm at hatching, but disappears after three days. Hatchlings apparently do not overwinter in the nest, and move directly to water after leaving the nest. In the Conecuh and yellow rivers, free-living, recently hatched juveniles have carapace lengths ranging from 34 to 44 mm (mean 40.8) when collected in late September.
Hatchling Graptemys ernsti begin feeding shortly after entering the water. Individuals less than 100 mm in carapace length are essentially insectivorous. The fecal samples of turtles collected by Shealy (1976), including adult males, contained Trichoptera, Coleoptera, Odonata, Hymenoptera, and millipedes. Females shift to mollusks, including gastropods and the imported mussel Corbicula maniliensis, at a carapace length of 90-100 mm, and Corbicula composes at least 95% of all food consumed by adult females. Females under 150 mm prey mostly on mussels from 2 to 12 mm in length, and females over 150 mm utilize all sizes of mussels, especially those 5-20 mm long. Females over 220 mm feed primarily on mussels 15-25 mm in length. The remainder of the female diet is composed of native mussels (usually smaller than 50 mm), aquatic snails, and occasionally crayfish. Adult males are primarily insectivorous, but 15% of the fecal volume of a sample of 11 turtles was composed of small aquatic snails, and some small Corbicula shells were also observed (Shealy, 1976).
IUCN Red List Status (1996)
Lower risk: near threatened.