San Francisco State University
Department of Geography

Geography 316:  Biogeography        In progress 10/16/2002

The Biogeography of the Red-Eared Slider (Trachemys scripta elegans)

by  Lynna Grijalva,  student in Geography 316, Fall 2001

 
Taxonomy Classification:

Kingdom:  Animalia
  
Phylum: 
Chordata
      Class:  Reptilia
         Order:  Testudines
            Family:  Emydidae
               Genus:  Trachemys 
                  Species:  Trachemys scripta 
                     Subspecies:  T. scripta elegans 

 

   Juvenile red-eared slider  (Source: Vosjoli 1992) 

Description of Species:
The red-eared slider (T. scripta elegans) is one of three subspecies of the pond slider family in the United States. This medium-size turtle gets its name from the broad reddish stripe behind its eyes. The undersurface of its chin is rounded and there is a V-shaped notch at the front of its jaw that is not flanked by cusps. Most of its body is dark olive green with thin yellow green stripes and bars on the top of its shell (carapace), legs and face. The green coloration of the carapace on a juvenile becomes masked by black pigmentation with age, making older individuals, especially males, appear almost black with no visible  markings. In fact, these mature males are so different in appearance that they once were considered a separate species (Ernst, Lovich and Barbour 1994). The carapace is smooth, oval in shape and flattened with a weak keel. The bottom of its shell (plastron) is primarily yellow with a dark marking on the center of each scute. All the subspecies of sliders have webbed feet that aid this aquatic turtle in swimming. They average in length from 5 to 8 inches with a record of 11.38 inches (Dawson 1998). The male is usually smaller than the female with a much longer and thicker tail. The cloacal opening of the male is beyond the edge of the carapace while the female’s opening is at or under the rear edge of the carapace. Males have longer, curved claws that they use in courtship/mating (Conant and Collins 1991).  

(Source: Smith, Hobart and Edmund 1982)

                 Male                    Female

(Source: Bartlett and Bartlett 1996)

Habitat:
Red-eared sliders inhabit most freshwater systems such as lakes, streams, swamps, ponds and rivers. They prefer the quiet waters of marshes, sluggish rivers and ponds that have soft bottoms with numerous basking sites and an abundance of aquatic vegetation. They are faithful to home ranges, leaving only to search for mates, nest and hibernate. Even if the waterways in their home ranges begin to evaporate during the summer, the sliders remain. Only after the waterway is completely dry and conditions become unbearable, will they migrate to better areas (Ernst, Lovich and Barbour 1994).

Adult red-eared slider  (Source: Wieke 2000)

Natural History:

Reproduction

Male sliders become sexually mature when they are between 2 and 5 years old and are about 4 inches long. Females take longer to mature, reaching maturity when they are 5 to 7 years old and 6 to 7.5 inches long. Mating and courtship usually occurs between March and June (Dawson 1998).

Male sliders have a unique mating ritual. When a sexually active male finds a swimming female, he maneuvers in front of her, stretches out his front feet, and vibrates his long claws on the female’s head and neck in a courtship like dance. The female often continues to swim forward while the male swims backwards. If the female is receptive, she will eventually stop swimming and sink slowly to the bottom. The male follows and climbs on top of the female. He holds her carapace with all four claws and bends his tail under hers. During this time the male may bite the female on the neck. Once in place, the male lets go with his front legs and swims backwards until he his nearly in vertical position. From this position mating occurs and lasts about fifteen minutes. Three to four mature males may court the female simultaneously. During courtship, these mature males are occasionally aggressive toward one another (Ernst and Barbour 1989).

Female sliders will typically nest in May and June. A female may have 1 to 3 clutches a season, with second clutches laid in July and August. Females will often travel some distance to find a suitable nesting site. Nests are dug in the soil with the female’s back feet, typically in the late afternoon or early evening. Four to 23 white eggs with leathery shells are laid in a 3-10 inch wide by 2-4 inch deep hole. The hole is then covered with displaced soil to seal in the eggs for protection from predators and the elements. Predators like skunks and raccoons frequently rob the nests while ants, fly maggots and molds attack the eggs. Larger females often lay more eggs in a clutch than smaller females. Hatchlings emerge in 60 to 75 days using their carnucle (egg tooth) that soon disappears after the hatching. Hatchlings are born between the months of July and September.  However, if hatching occurs in the late fall, the young may overwinter in the nest and emerge the following spring. Juveniles are around one inch long upon hatching. Predators such as fish, frogs, snakes, carnivorous turtles, large wading birds, and various mammals eat hatchlings. Sliders grow quickly when young, reaching about 2 inches within one year. As they get older, their growth slows. Gars, crows, mink, raccoons, otters and coyotes prey on adult sliders. Adult sliders may live up to 30 years in their natural environment (Dawson 1998).
 
Behavior

Sliders are cold-blooded and spend most of their day basking on logs, rocks, or stumps near the water. Sometimes you can see sliders stacked on top of each other three high in the late morning to mid-afternoon. Sliders bask for several hours at a time. Individuals often share their basking spot with other sliders and other species of semi-aquatic turtles. Sliders have poor hearing but are very sensitive to vibrations. Sliders may nap while basking but are very alert. The name “slider” refers to the quick retreat from their basking site into the water when they feel even the slightest bit threatened. Sliders will sleep at night underwater, usually resting on the bottom, clinging to submerged limbs or floating on the surface using their inflated throat as a flotation aid (Ernst, Lovich and Barbour 1994).

Sliders become inactive in October, when temperatures drop below 50° F (10° C). Individuals often hibernate underwater, but have also been found under banks and hollow stumps. Sliders do not hibernate in groups, unless forced to because of the lack of a suitable hibernation area. Hibernation is not uninterrupted, during warm spells in January and February, they become active and surface to bask. However, when the temperature begins to drop again, they quickly return to their hibernation area. Sliders emerge for good in early March or late April (Dawson 1998). 

Food Habits

Young sliders tend to be more carnivorous than adults; eating about 70% animal matter and 30% plant matter. Adults eat 90% plant matter and 10% animal matter (Wilke 1979). Foods include aquatic snails, tadpoles, crawfish, fish, crustaceans and mollusks. They also eat plants like arrowhead, water lilies, hyacinths and duckweed. Feeding occurs under water, usually late in the afternoon (Dawson 1998).

 

Evolution:
There are disagreements and disputes about the origins of turtle species. However in 1999, molecular biologists found evidence from two nuclear genes, and analyses of mitochondrial DNA and 22 additional nuclear genes, that join crocodilians with turtles and place squamates at the base of the tree (Rieppel and Hedges SB, 1999). Molecular time estimates support a Triassic origin for the major groups of living reptiles. The time estimates indicate that turtles diverged from crocodilians at 207 + 20.5 mya (Rieppel and Hedges 1999). These divergence times are close to when the first turtles (223 to 210 mya) and crocodilians (210 to 208 mya) appear in the fossil record (Rieppel 1999).        

A molecular phylogeny of reptiles

Fossils indicate that turtles first appeared on the earth around 200 million years ago, during the Upper Triassic period. The first known turtle was the Proganochelys quenstedli. It had a fully developed shell and a turtle-like skull and beak. However, Proganochelys also had several primitive features not found in turtles today. The features include a simple ear, a clavicle and small teeth. These turtles were unable to withdraw their heads or legs into their shell. By the middle of the Jurassic Period, turtles had split into the two main groups of turtles found today, the arched-necked turtles (pleurodires) and the side-necked turtles (cryptodires). Modern side-necked turtles are found only in the southern hemisphere and withdraw their heads sideways under the shell. Arch-necked turtles retract their heads in an S-shaped curve. Scutemys was one of the first arch-necked turtles. The descendants of Scutemy include: the box, pond, subaquatic turtles, as well as turtles and soft-shelled turtles (Dawson 1998). Pond turtles (including red-eared sliders) belong to the Emydidae family (Maylan 1997). 

 

Distribution:

Three of the thirteen to nineteen subspecies of the pond slider family are native to the United States. These subspecies are: Trachemys scripta scripta, the yellow-bellied slider; Trachemys scripta troosti, the Cumberland slider; and Trachemys scripta elegans, the red-eared slider. The yellow-bellied slider ranges from southeastern Virginia to northern Florida. The Cumberland slider is found in the upper portions of the Cumberland and Tennessee Rivers, from southeastern Virginia and Kentucky to northeastern Alabama. And the red-eared slider occupies the Mississippi Valley from Illinois to the Gulf of Mexico. Where the ranges of the three North American species meet, interbreeding has established zones of intergradation (Conant and Collins 1991).

All non-native occurrences of the yellow-bellied, Cumberland and red-eared slider are attributed to either accidental escape from pet brokers or intentional or accidental release of pets. As a result, these subspecies have established themselves in various states within the United States and other countries around the world. The distribution pattern of these subspecies is disjunct due to: (1) their release in various locations; and (2) their faithfulness to home ranges once they have established themselves. 

The red-eared slider in particular, has successfully established itself in the United States east, north and south of its native range. The four states east of its native range include Arizona, California, Oregon and Hawaii. The state south of its native range is Florida. The eight states north of its range include Kentucky, West Virginia, Ohio, New Jersey, Pennsylvania, Michigan, Maryland and Massachusetts. Other countries that the red-eared slider has been introduced to include Japan, South Korea, Guam, Thailand, Germany, France, South Africa, Israel and Australia (Ernst, Lovich and Barbour 1994).

Map of Distribution
Illustration by Lynna Grijalva  (Source: Ernst, Lovich and Barbour 1994) 

 

Other interesting issues:
 
    Sliders, especially the red-eared slider were once the most popular turtle item in the pet trade, and an estimated 5-10 million turtles were exported around the world. (This is why sliders are referred to as the “dime store turtle”). Because of unsanitary conditions and a lack of knowledge on turtle care by the pet store owners and their purchasers, few survived for long in captivity. Soon turtle farms were established in the southeastern United States (mostly in Louisiana and Mississippi) in response to declining wild stocks. By 1960 more than 150 farms were operating. Unfortunately, these farms were not self sufficient and over 9,000 adults were taken from the wild each year, seriously depleting natural populations in some areas. (In recent years, these same farms are also responsible for trapping adult sliders to export as food to Asia (Smither 1998)). In 1975 the U.S. Food and Drug Administration banned the sale of turtles under “four inches” carapace length in the United States and Canada because they transmitted the disease salmonellosis caused by the bacteria Salmonella (Ernst, Lovich and Barbour 1994). Salmonellosis is a serious disease of the digestive tract that infected several thousand children and caused a number of deaths that have been attributed to their handling of turtles (Vosjoli 1992). 

The turtle pet trade industry has continued to export large number of hatchlings and adults to other countries using various techniques to limit Salmonella. The use of the antibiotic Gentamicin has led to the development of many antibiotic-resistant strains. An estimated three to four million turtles continued to be exported, thus providing an important potential route for global dissemination of human salmonellosis (Ernst, Lovich and Barbour 1994).                                                                                                      

Because millions of red-eared sliders are produced annually for sale outside of the United States and because hobbyists have an interest in selectively breeding color morphs with aesthetic appeal, several color morphs are now available in the specialist reptile trade. The most popular are the albino red-eared sliders which as juveniles are bright lemon yellow with the prominent orange-red patches on the side of the head. As they grow into adults, the yellow tends to fade into a cream-yellow. Most of the other morphs of red-eared sliders are sold under the general category of  “pastel” red-eareds. The term pastel has been applied to a wide variety of color morphs of red-eared sliders characterized by varying degrees of hypomelanism (reduced black), hypoxanthism (reduced yellow), aberrations in pattern and varying degrees of yellow and red pigmentation. Many pastel sliders have asymmetries and defects that suggest either incubation at inadequate temperatures or the expression of recessive genes. Examples include asymmetry of shell pattern and/or scutes, reduced size of one or both eyes and unusual enlargement of one or both eyes (Vosjoli 1992). 

Pastel red-eared slider  (Source: Vosjoli 1992)

Albino red-eared slider  (Source: Bartlett and Bartlett 1996)

        

Conservation:

Humans are the greatest enemy of red-eared sliders. Every year untold numbers of juvenile and adult turtles are shot while basking, being beheaded after being hooked by uninformed fisherman, crushed as they wander across highways, sacrificed for researching and teaching, lost to the pet and food industries, or dying from habitat destruction and pollution (Ernst, Lovich and Barbour 1994). If you find yourself in possession of a red-eared slider, and feel that you can no longer care for it properly, please do not release your captive turtle into the wild. Not only is this illegal, but it can be harmful to your domestic turtle who is probably accustomed to being fed store bought turtle food. Also by releasing your red-eared slider, your turtle may pass parasites onto the surrounding turtle population. In addition, your turtle may mate with another turtle of its kind, establish a colony and push out the native species living in the area. In short, releasing your domestic turtle could have a serious effect on the environment, drastically impacting conservation efforts. The following two websites include organizations that will accept red-eared sliders for adoption and post red-eared sliders that can be adopted:
 

 http://www.turtlehomes.org/usa/red_ear_slider_adoptions.shtml

http://exoticpets.about.com/gi/dynamic/offsite.htm?site=http%3A%2F%2Fwww.geocities.com%2F%7Ecorr98%2F

 

 Bibliography: 

Conant, Roger and J.T. Collins. 1991. Peterson Field Guides: Reptiles and Amphibians of Eastern/Central North America. Boston, MA. Houghton Mifflin Co.  

Bartlett, R.D. and Patricia P. Bartlett. 1996. Turtles and tortoises: everything about selection, care, nutrition, breeding and behavior. Hong Kong. Barron’s Educational Series, Inc.

Dawson, Jeff. 2000. Slider. [On-line]. The Turtle Pages. Available: http://theturtlepages.crosswinds.net/species/t_scripta/index.html [10/10/01].

Dawson, Jeff. 2000. Evolution of Turtles. [On-line]. The Turtle Pages. Available: http://theturtlepages.crosswinds.net/evolution [11/08/01].

Ernst, Carl H., Jeffrey E. Lovich, and Roger W. Barbour. 1994. Turtles of the United States and Canada. Washington, D.C. Smithsonian Institution Press.

Ernst, Carl H., Roger W. Barbour. 1989. Turtles of the World. Washington, D.C. Smithsonian Institution Press.

Maylan, Peter A. and Eric Ganko. 1997. Polycrptodira. [On-line]. Eckerd College. Available: http://spider.eckerd.edu/turtles/polycryptodira/polycryptodira.html/ [10/24/01].

Rieppel, Olivier. (1999). A Commentary Piece from the Journal of Science, 1999 Feb12;283(5404): 998-1001 on the Prion Gene found in Turtles, by Hedges SB, Poling LL. [Online]. A webmaster publication. Available: http://www.mad-cow.org/00/mar00_turtle.html [11/08/01].

Smith, Hobart M. and Edmund D. Brodie, Jr. 1982. Reptiles of North America: A guide to field identification. New York, NY. Golden Press.

Smither, Bob. 1998. The Red Eared Turtle - Trachemys Scripta elegans. [On-line]. Gulf Coast Turtle & Tortoise Society. Available:
http://www.gctts.org/RedEaredTurtle/index.html [10/24/01].

Vosjoli, Phillipe de. 1992. The General Care and Maintenance of Red-Eared Sliders and other Popular Freshwater Turtles. Singapore. Advanced Vivarium Systems.

Wilke, Hartmut. 1979. Turtles. Munich, West Germany. Grafe & Unzer Gmbh.

Wilke, Hartmut, 2000. Turtles: Everything about Purchase, Care, Nutrition and Behavior. Hong Kong. Barron’s Educational Series, Inc.

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