Search Nature Watch

Sunday, August 4, 2013

Turtle Teachings

Texas Cooter, Pseudemys texana

Hardly a day goes by in the summer months when you can't find a turtle basking in the sun.  Like other reptiles, turtles are cold-blooded or ectotherms, who vary their internal temperature according to the ambient environment.  Turtles have been around for over 250 million years, even longer than their snake and lizard relatives.  We tend to use the word turtle for all freshwater and some land-dwelling species, while tortoise is used only to describe members of the true tortoise family.

Red-eared Slider, Trachemys scripta elegans
The shell of a turtle has two parts:  the upper is called the carapace, while the lower is called the plastron.  Many turtles have a bony bridge that connects the top and bottom and lends strength and rigidity to the structure.  Carapaces of turtles vary widely, and shape, colors, and patterns are among the field marks that often distinguish one species from another.  Scutes, from the Latin scutum or shield, are the plates which cloak the outside of the turtle's shell.  Most turtles have 54 scutes, with 38 covering the carapace, and 16 covering the plastron.  Made from the protein keratin, scutes can be thought of as the epidermis that covers the bony shell.  It is even possible, by counting the stack of smaller, older scutes on top of the larger, newer ones, to estimate the age of a turtle.  The accuracy of this method, however, is somewhat muddled by the variable growth rate of the scutes and the fact that, like fingernails or horns, they eventually fall away from the shell.  

Texas Cooter, Pseudemys texana
Regardless of the length of a turtle’s neck, they all have 8 vertebrae.  In spite of their highly muscular necks, turtles are often called ‘hidden-necks’, for their ability to retract their head and neck into the shell by bending it into a vertical S-curve and withdrawing from sight.  Some species like box turtles go even further, and gain an added degree of protection from predators by having a hinge in their plastron, dividing it into two lobes, and giving them the ability to draw up those lobes and completely seal the turtle inside.

Eastern Box Turtle, Terrapene carolina
Turtles may spend most of their life in or around water, but they breathe air and often range widely when searching for a mate in the warmer months.  With smell being the keenest sense possessed by a turtle, the males will chase any object of approximately the correct size, and once close, will use smell to determine if the object is a female of the same species.  Pregnant females will dig a hole, often called a body pit, and deposit eggs in the hole, covering them with dirt.  In some species of turtles, temperature determines whether an egg develops into a male or a female, with a higher temperature producing a female and a lower temperature producing a male.  Hatchlings squirm their way to the surface and head toward water alone, as there is no known turtle species where the female cares for the young. 

Spiny Softshell Turtle, Apalone spinifera
The more common turtles you will see in central Texas include the Common snapping turtle (Chelydra serpetina), Eastern box turtle (Terrapene carolina), Red-eared slider (Trachemys scripta elegans), Texas map turtle (Graptemys versa), and the Spiny softshell (Apalone spinifera).  All but the box turtle are generally found in wetlands, ponds, streams, and lakes where heavy vegetation is present, although box turtles are activated by rain events. 

Symbolically, the turtle has represented patience, strength, endurance, stability, and protection to many native peoples, who have observed the often slow but deliberate life of the turtle.  This is a fascinating fact, since researchers have recently discovered that turtles’ major organs, such as the liver, lungs, and kidneys, do not gradually break down or become less efficient over time.  Understandably, this has inspired geneticists to begin a detailed study of the turtle genome, hoping it can unlock the secrets of longevity!