3- The six-lined racerunner (Aspidoscelis sexlineata)
The six-lined racerunner (Aspidoscelis sexlineata) is a species of lizard native to the United States and Mexico.
Male six-lined racerunner (Aspidoscelis sexlineata).
Conservation status :
Least Concern (IUCN 3.1)
Scientific classification :
Lacerta sexlineataLinnaeus, 1766
Cnemidophorus sexlineatus— A.M.C. Duméril & Bibron, 1839
Aspidoscelis sexlineata— Reeder et al., 2002
Geographic range :
The six-lined racerunner is found throughout much of the southeastern and south-central portion of the United States, from Maryland to Florida in the east, across the Great Plains to southern Texas and northern Mexico. The species' range also reaches north to Wisconsin and Minnesota. A small disjunct population is found in Tuscola County, Michigan.
The six-lined racerunner is typically dark green, brown, or black in color, with six yellow or green-yellow stripes that extend down the body from head to tail. The underside is usually white in color on females, and a pale blue in males. Males also sometimes have a pale green-colored throat. They are slender-bodied, with a tail nearly twice the body length.
Like other species of whiptail lizards, the six-lined racerunner is diurnal and insectivorous. They are wary, energetic, and fast moving, with speeds of up to 18 mph (29 kmh), darting for cover if approached.
Due to its extensive range, A. sexlineata is found in a wide variety of habitats including grasslands, woodlands, open floodplains, or rocky outcroppings. It prefers lower elevations, with dry loamy soils.
Breeding takes place in the spring and early summer, with up to six eggs being laid in mid-summer and hatching six to eight weeks later. A second clutch of eggs may be laid several weeks after the first.
There are three recognized subspecies of A. sexlineata:
Eastern six-lined racerunner, Aspidoscelis sexlineata sexlineata (Linnaeus, 1766)
Texas yellow-headed racerunner, Aspidoscelis sexlineata stephensae Trauth, 1992
Prairie racerunner, Aspidoscelis sexlineata viridis Lowe, 1966
Adult, Indialantic, Florida
Conservation status :
The six-lined racerunner is listed as a species of concern in the state of Michigan, due to its limited population but otherwise holds no official conservation status.
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Six-lined Racerunners (Aspidoscelis sexlineata)
Eastern Six-lined Racerunner
Aspidoscelis sexlineata sexlineata
Common Name: Eastern Six-lined Racerunner
Scientific Name: Aspidoscelis sexlineata sexlineata
Species: sexlineata consist of two Latin words sex meaning "six" and lineata meaning "of a line". This refers to the six light longitudinal lines found on the dorsum.
Subspecies: sexlineata consist of two Latin words sex meaning "six" and lineata meaning "of a line". This refers to the six light longitudinal lines found on the dorsum.
Average Length: 6 - 9.5 in. (15.2 - 24.1 cm)
Virginia Record Length: 9.7 in. (24.7 cm)
Record length: 9.7 in. (24.7 cm)
PHYSICAL DESCRIPTION: The maximum known snout to vent length (SVL) and total length are 75 mm (3.0 in.) and 241 mm (9.5 in.), respectively, making this a moderately sized lizard. The maximum known SVL and total length in Virginia are 76 mm (3.0 in.) and 247 mm (9.7 in.), respectively. In a Virginia sample, the tail length was 63.3-78.6% of the total length. Dull, tiny, granular, dorsal scales do not overlap each other. In contrast, the ventral scales (plates) are large, quadrangular, and in eight regular, longitudinal rows. Plates in the midventral row number 29-36. Around the midbody, granular scales number 82-103. Supralabials are 7/7, 7/8, 8/8, or combinations of 6-9. There are no supranasals, and paired nasal scales separate the rostral from the frontonasals. There is a single mental, and there is one postmental. There are 23-34 femoral pores. On the right fourth toe, the lamellae number 20-31. On the tail, scales are rectangular. There are six narrow, whitish to yellow or bluish lines on a dark back. These stripes all start behind the eyes. A large, tan to light brown stripe goes from the head down the middle of the back to the base of the tail. The tail is long and slim, bluish in the young but brownish to gray in adults. Between the dorsolateral stripes, there are 6-13 scales. At the base of the tail, the dorsolateral stripes end, but up to about one third the length of the tail from its base, the two lateral stripes end. Dorsally, the tail is brown. Laterally, with two light lines, the tail is dark brown. The venter of the tail is a cream to bluish color. Dorsally, the coloration of the head varies from light brown to tan. The venter of this skink varies in color from cream to bluish *1014,10760*.
SEXUAL DIMORPHISM: Of the body size in adults, females are slightly larger than males. In females, the average ratio of tail length to total length is lower than that in males. Around the midbody, the number of granules average lower in females than in males. Females usually have a whitish venter, while males usually have a bluish one *10760*. Juveniles: Except for a bluish tail and a usually cream-colored venter, juveniles are similar to adults in pattern and color. As individuals age, the bluish color of the tail fades to a brown or gray color. In a North Carolina sample, hatchlings averaged in size at 32.5 mm SVL, 93.5 mm total length, and 0.84 g in body mass. In Virginia, hatchling size is unknown *10760*.
CONFUSING SPECIES: The skinks in the genus Plestiodon are the only other lizards in Virginia that have striped legs. Except for old males, skinks have five stripes. Also, the scales of skinks are broad, shiny, and overlapping *10760*.
REPRODUCTION: Hatching is from late June to September. The older females lay two clutches per season. The eggs are laid a few centimeters below the surface and sawdust piles are a favorite nesting site. The eggs number five to six with the number being dependent on the size of the female *1014*. The species is ovipararous *4218*. According to observations in North Carolina and other southern states, females nest by constructing shallow burrows in loose, sandy soil and sawdust piles from late May through June. In Virginia, females with oviductal eggs were found from late May to mid-June. Based on enlarged follicles and oviductal eggs, clutch size was found to be 1-5 eggs. Observations in the North Carolina Piedmont found 1-5 eggs per nest. Maximum clutch size was found to be 8 in a study by Trauth. Males will forcibly mate with females after following female trails, and sometimes, after digging females out of burrows. At 52 mm SVL, a female was found as the smallest mature female with developing follicles. At 51 mm SVL, a male was found as the smallest mature male with an enlarged testis. The eggs are not tended to by the females, and there has been no record of communal nesting in this species. In a North Carolina sample, egg size and mass averaged 16.3 x 9.3 mm and 0.78 g, respectively. In the same sample, after incubating about 60 days, the eggs hatched between 27 June and 5 September. In Virginia, the egg measurements and hatching dates are unknown *10760*. In a South Carolina study, a population of this species revealed a density of 2.5 individuals per 100 sq. meters, and growth rates for females and males were 0.058 mm per day and 0.045 mm per day, respectively. A Kansas population studied by Fitch proved to have a density of 140 individuals per hectare, 41% was the annual survivorship rate, and six years was the maximum life span *10760*.
BEHAVIOR: Activity is diurnal *4218*. This is a highly active lizard. It sprints under vegetation and into burrows in order to escape from predators and observers. Territorial behavior does not exist in this species. Studies of the western subspecies in Oklahoma revealed that males and some females displaced, chased, and bit other individuals of the same sex in efforts to form loose, linear dominance heirarchies. In Virginia, aggressive behavior among individuals of the eastern subspecies has not been documented *10760*. Unlike skinks and glass lizards, racerunners do not autotomize their tails. Though the majority of Virginia specimens had complete tails, some had incomplete, unlike the samples of skinks. The tail helps with balance when running. It does not help, at least in adults, to distract predators *10760*.
References for Life History :
1014 - Martof, B.S., Palmer, W.M., Bailey, J.R., Harrison, III J.R., 1980, Amphibians and Reptiles of the Carolinas and Virginia, 264 pgs., UNC Press, Chapel Hill, NC
4218 - Parker, S.P., 1982, Six-lined racer (temp. title)
10760 - Mitchell, J. C., 1994, The Reptiles of Virginia, 352 pgs., Smithsonian Institution Press, Washington, DC
Other websites :
Six-lined Racerunner Sand Dance
Six-lined Racerunner (Cnemidophorus sexlineatus)
Six-lined Racerunner 08/01/13
Six Lined Racerunner Making A Bed
Brandon's Herp Adventures: Six-Lined Racerunner
Teiidae family :
Teiidae family :