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The turtle, he is an elusive creature. Hidden well in the water. He is also hidden well in his shell. The shell alone provokes our childlike curiosity to see what?s inside, to explore. The more we learn about them the more questions we have. How do they live, how do the reproduce, how do they as cold blooded reptiles survive the winter, and many other mysteries. Science has begun to solve some of these problems, but new problems appear every day. Turtles are very interesting animals. One of the most fascinating species of turtles is the Painted turtle.
The Painted turtle is a reptile that lives mainly in north America. It can also be found in Nova Scotia. The species is divided into four subspecies each with their own distinct location. Chyrsemys picta picta (Eastern Painted turtle) located mostly between the Atlantic ocean and the Appalachian mountains. Chyrsemys picta marginata (Midland Painted turtles) located mostly in the great lakes, Ohio valley and all the way down to northern Alabama. Chyrsemys picta dorsalis (Southern Painted turtles) who live dependent on the Mississippi from southern Illinois to the gulf of Mexico. The last subspecies is Chyrsemys picta belli, the Western Painted turtle. These are the painted turtles that live here in Nebraska. They have the largest range of any of the painted turtle species, spanning from the Mississippi all the way to Washington and British Colombia (Dawson, 1998). Painted turtles can generally be distinguished from other turtles by several identifying characteristics. They have a smooth flattened carapace (top shell) that can be brown, olive or black. The carapace can have light yellow or orange lines. The Painted turtles plastron (lower shell) can be creme, yellow or tan. They resemble red eared sliders because they have lines on their head and neck. A Painted turtle however has yellow streaks on the face and red on the neck while a slider has red on the face. Also, females of the species tend to be generally larger than the males (Janzen, 1994). This is a common characteristic among reptiles.
The diet of all painted turtles varies according to their place in their life cycle. They are carnivores, omnivores and even herbivores during different stages of their lives. A hatchling is almost exclusively a carnivore, with insect larvae and beetles for an average meal. As they mature they begin to dine on plants, while still retaining the carnivorous appetite of their youth. Finally in the latter stages of their lives they give up meat almost entirely and feed primarily on duckweed, algae and lily pads (Dawson, 1998). The animals spend much of the day basking in the sun. They share basking sights. It is not uncommon to see thirty of them on the same log. They prefer to live in soft bottom muddy lakes, swamps, slow moving streams and rivers (Dawson, 1998).
Turtles in general have fairly long life cycles. Captive Painted turtles have been known to live well over twenty years. In the wild life expectancy is closer to eight to ten years. For females it takes four to eight years to mature. Males mature much faster reaching reproductive size within two to five years. The age is less important than the size of the actual turtles. When a turtle reaches a certain size it becomes able to reproduce. The time between the expected death and maturation of the females there are only one or two years of reproduction. Courting takes place in April and May, in colder regions the time can be delayed almost all of the way to early autumn. The male swims backward in front of the female while vibrating his claws on her cheeks. Once the sperm has been transmitted to the female she has the ability to postpone fertilization of the eggs, if needs be, for months, even years. This type of adaptation allows the mother to choose when it is safe to lay her eggs (Dawson, 1998). This is a very important item in a creature who?s body temperature is directly controlled by its environment. The eggs are laid in July or August, it takes them about ten to eleven weeks to hatch. Eggs are soft and leathery and are generally about 1.25 inches long. An average clutch of eggs is about ten. However, the number is in direct proportion to the size of the female. A large female may lay up to as many as twenty eggs. The nest is relatively close to the surface, only two to three inches below topsoil. This allows for maximum heating, but also for a layer of insulation against the winter cold. Reproduction is the most important thing in the life most animals, assuring the survival of your own species.
Painted turtles, like many reptiles, are creatures with temperature dependent sex determination (TSD) (Bull, 1980). In other words, while in the nest, the ambient temperature determines the sex of the eggs. A large part of this equation is vegetation cover. A heavily covered region will not receive as much solar exposure. Less exposure to the sun equals a cooler nest. Also with the nests close to the surface of the soil, they are more influenced by the weather. Clouds or rain or a sunny day would all have drastic effects on the temperature of the eggs. It is assumed that a female painted turtle can sense the coming weather somewhat (Janzen, 1994). In a recent study it was shown that Painted turtles were a temperature dependent species. “The majority of nests each year (66% overall) produced hatchlings of only one sex. Most unisexual nests in 1989 and 1991 were female oriented.; all unisexual nests in 1990 and 1992 were male oriented” (Janzen, 1994). Also it was determined that warmer temperature, or areas with less vegetation produce primarily female clutches. Whereas places that were cooler or had more vegetation produced primarily male hatchlings. This may be one way nature prevent inbreeding in the species. With such a large percentage of animals in a clutch being the same sex it becomes very unlikely that inbreeding will occur. This adaptation also gives the females an interesting advantage. It allows them to control the flow of male vs. female addition to the population. They have the ability to choose nesting sights based on probable outcome of the clutch.
One of the most interesting aspects about Painted turtles is their ability to survive the winter months frozen. The hatchlings emerge from their shells in September or October. However they do not immediately leave the nest. They will remain in the nest during winter and emerge in the spring. Inside the nest the air is insulated and so is a bit warmer, usually about eighteen to twenty eight degrees F. This is still well below the freezing temperature of turtle blood, about thirty one degrees (Storey, 1992). In an experiment, hatchlings temperature was slowly reduced. When the body temperature of the hatchlings hit 26.5 they literally froze. “When hatchling turtles freeze, ice first forms on the outer skin. Over the next several hours ice grows inward toward the body core, gradually cutting off blood circulation to the periphery, until only the central heart-brain corridor is serviced. Ultimately, even this circulation is lost, and eventually there is no muscle movement, no breathing, heartbeat, or blood flow, and only minimal brain activity. Soon after the animals thaw however the vitals resume one after another” (Storey, 1992).
This is an amazing phenomenon that is observed in no higher form of life than the Painted turtle. They are able to do this for two reasons. First special de icing proteins are made in the liver. Also the level of glucose goes up within the cells. The higher level of glucose lowers the freezing point of the liquid inside the cell so it does not freeze (Science News, 1987). In fact only about fifty two percent of the hatchlings body water freezes (Storey, 1992). This amazing adaptation allows the painted turtle to live in colder temperatures than any other reptile (Science News, 1987).
When Painted turtles mature they no longer have the ability to “freeze”. They must develop other ways to survive the harsh winters. Adults prefer to hibernate in temperatures between thirty seven and forty three degrees F. In order to find a place that remains at that higher temperature the turtles must have more insulation. They usually burrow into the mud in the bottom of shallow water. These places do not usually completely freeze over and if they do then the turtles move deeper. That solves the temperature issue but how does an animal that requires air to breath stay underwater for two months? They accomplish this feat through two processes. First “when a turtle is submerged the oxygen content of its blood falls rapidly to near zero. A level that would be fatal to humans in three or four minutes. They are able to do this because they store glycogen. Glycogen can be broken down to provide energy without using oxygen. Second they enter a condition known as metabolic arrest. It is a condition where a cells use of energy is greatly reduced. This allows the organism to go for longer periods on stored nutrition (Storey, 1992).
The more we learn about Painted turtles and all forms of life the closer we get to understanding ourselves and the way that we came to be. Nature continues to astound us with the solutions to new problems. Within these little turtles may be the answer to cryogenics, or to frostbite. There are innumerable bonuses to every new bit of information that we learn. While we may never learn all there is to know, we can know more.
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