River cooter turtles,, are native to North America. They are most commonly found in eastern and central parts of the United States. They are found as far north as northern Ohio and extend as far south as northern Florida in the Florida Panhandle. The distribution of these turtles is from eastern Virginia, westward to eastern Texas. Disjunct populations of river cooters can be found in the New River in Virginia and West Virginia, and the Tennessee River in Tennessee and eastern Kentucky.
River cooter turtles are primarily found in permanent bodies of freshwater such as rivers and lakes. On rare occasions, these turtles also can be found in ponds, springs, swamps, and even saltwater tributaries. The habitats of these turtles are laden with various types of aquatic plants and marine flora. Though shallow in nature (0-2 meters), these habitats often are moderately inaccessible to humans in order to protect the turtles from anthropogenic disturbances and predation attempts. River cooter turtles also spend part of their lives on land. Activities such as basking and nesting typically take place in terrestrial environments within 30 meters of the waters in which these turtles spend the majority of their time. (Ernst and Lovich, 2009; Rivera, 2008; Van Dijk, 2016)
Upon hatching, river cooter turtles range from 27 and 39 mm in length, and weigh from 5.2 to 14g. When newly hatched, these turtles are a bright green color with light markings. As they mature, their makings tend to darken. At maturity, shell lengths as long as 43.7 cm have been observed, and turtles can with weigh up to approximately 5 kg.
Overall, the shells of adult turtles are relatively flattened, elongated, and oval-shaped with light and dark brown markings. Each shell is distinctively different, but most include green, yellow, brown, and black patterns. Sexual dimorphism can be seen in these turtles, with adult females being larger on average (average carapace length of 287 mm) than adult males (average carapace length 223 mm). Additionally, the shells of male river cooters are flatter than that of females. Males also possess elongated fore claws as compared to females.
Another factor that has influenced the physical characteristics of river cooter turtles is the strength of different water currents. The shells of these turtles form higher or lower drag morphologies relative to the strength of the current in their specific habitat. Those that adapt to form flatter shells in order to prevent dislodging of the shell from the body often have weaker shells than those that have the typical dome-shaped shell. (Aresco and Dobie, 2000; Dreslik, 1997; Ernst and Lovich, 2009; Rivera and Stayton, 2011; Van Dijk, 2016)
In general, the rate of embryonic development of river cooter turtles depends on the temperature at which the eggs are incubated. The eggs are typically incubated for a period of 80 to 150 days, depending on temperature and location of the nesting site. In a laboratory experiment by Dormer et al. (2016), eggs incubated at 30ºC hatched three weeks earlier, showed more advanced embryos, and grew to hatchling size faster than eggs incubated in colder (26ºC) temperatures. Although there are differences in the rate of embryonic development of these turtles depending on incubation temperature, temperature has no impact on final hatchling size. Within the genus Pseudemys, several turtles experience sex determination due to incubation temperature. When temperatures are cool, a higher proportion of the hatchlings are males, and when temperatures are warm, a higher proportion of hatchlings are females. Based on the research of Ewert and Nelson (1991), 100% of river cooter turtles incubated at 22.5ºC were males, 91% of river cooter turtles incubated at 25ºC were males, and 0% of the river cooter turtles incubated at 30ºC were males.
River cooter turtles typically produce 2 to 20 hard-shelled eggs per clutch. Of these eggs, the individual sizes of eggs can vary between 35.8 to 44.3 mm in length, and 22.5 to 27.6 mm in width. Newly hatched turtles can measure 27 to 39 mm, and can weigh from 5.2 to 14 g. When young river cooters hatch, they typically have lighter markings on their shells than adults , but these markings become darker with age.
In general, turtles have indeterminate growth, meaning that they grow throughout their lifetime. This growth slows between 7 and 15 years for males, and 13 to 24 years for females. (Bartlett and Bartlett, 1996; Congdon, et al., 2013; Dormer, et al., 2016; Ewert and Nelson, 1991; Iverson, 2001; Van Dijk, 2016)
When looking at relatives of river cooters from the same subfamily (Deirochelyinae), male and female turtles are generally polygynandrous, meaning that they have several different mating partners within one mating season. In the mating of river cooters, the male turtles pursue the females. In order to show their intentions to mate, they stick their necks out at each other and use their claws to touch each other’s faces and carapaces. In addition, if the turtles are in water, the male turtles occasionally swim above the females and bites at the edge of their shells. If the female is mutually interested in mating, she will swim to the substrate and allow the male to mount her and begin the mating process. As for the paternity of each specific clutch, up to 30% of clutches are likely fathered by multiple males. This is made possible by the fact that female turtles can store sperm for several weeks before fertilizing their eggs. (Ernst and Lovich, 2009; Green and Pauley, 1987; Iverson, 2001; Pierce and Avise, 2001)
For river cooter turtles, reproductive maturity is reached at 6 years of age in females and 13 years of age in males. The duration of their nesting season depends on the location of the nesting site. In warmer locations, such as South Carolina, the nesting period is shorter than it is in cooler areas, where the hatchlings may have to overwinter in the nest to avoid harsh temperatures. Nesting typically occurs from late-April to mid-July. Each year, between 1 and 6 clutches (2.3 on average) are hatched, and each clutch contains about 10 to 20 eggs (14.6 on average). Time between clutches can range from 2 to 12 months. Because female turtles can hold fertilized eggs for several months, the gestation period of turtles in general can vary from 10 weeks to 2 years. As a nesting place for their young, female river cooter turtles dig holes in sand or soil on elevated ground, where they deposit their eggs. The eggs of river cooters are oval shaped with hard pinkish-white shells, and are approximately 4 cm in diameter. The hatchling mass of river cooter turtles varies and can be from 5.2g to 14 g. Depending on the size and age of the mother turtles, the size of their eggs varies. Hatchlings are independent at birth. (Ernst and Lovich, 2009; Green and Pauley, 1987)
Among river cooter turtles, neither parent provides parental care beyond nesting. In this relationship, the single contribution of males is the use of his sperm for fertilization and the indirect impact he has on the genetics of his offspring. In nesting, females use their hind claws to dig a hole about 12 cm deep with an opening of about 7 cm in diameter, in which to deposit their eggs. The eggs are laid, covered in mud or soil, and the female river cooters return to the water. After approximately 90 to 100 days, typically around August and September, the turtle eggs hatch. (Ernst and Lovich, 2009; Green and Pauley, 1987; Pierce and Avise, 2001)
In captivity, river cooter turtles are known to live for an average of about 20 years, with the maximum age of captive river cooter turtles being 44 years. In the wild, these turtles often live approximately 40 years. ("AnAge: The animal aging and longevity database", 2014; Ernst and Lovich, 2009)
Across most of their range, excluding Florida and other areas with relatively warm winters, river cooter turtles are active from April to October. Outside of this period, turtles that live in colder climates hibernate for several months in the mud on the bottom of the rivers, lakes, and ponds, in which they reside. When hibernating, river cooters can stay underwater for up to two months without needing to make trips to the surface to breathe. In order to do this, they take in oxygen from the water through their cloaca. In their active months, they spend their daytimes basking. Other than basking, these turtles also participate in foraging and nesting during the daytime hours. Much time is spent submerged, resting on the substrate or moving about searching for food. Occasionally, these turtles must come up to breathe, but they are able to stay submerged for several hours between trips to the surface.
When mating, male river cooter turtles use extravagant displays to attract females. Males use their elongated claws to stroke the faces and carapaces of females, and occasionally bite at the backs of their shells while they are swimming. Males and females often mate with several partners during a single mating season. The female will swim to the bottom of the pond and the male will follow, mount her, and inseminate her.
These turtles are very skittish, and tend to remain in the water with the exception of basking and nesting. Typically, these turtles remain in their original waterbody and do not venture out to discover new areas. In the case of a habitat that is no longer suitable, such as a dried up water source, these turtles will make short trips on land directly toward a new permanent waterbody, where they will stay for as long as possible. (Buhlmann and Vaughan, 1991; Dreslik, et al., 2003; Ernst and Lovich, 2009)
The home range of river cooter turtles is very dependent on location. The approximate home range of river cooter turtles that live in ponds is 122 square meters. In riverine locations the turtles tend to have a larger home range of approximately 340 square meters. Males tend to move greater distances than females daily. (Dreslik, et al., 2003)
At this point, not much is known about the particular senses of river cooter turtles. Similar to other aquatic turtles, these turtles tend to be driven more by sight and hearing than by smell. When tested in a research setting, aquatic turtles in the Pseudemys genus were attracted to bright light and opaque blue color. In particular, these turtles were most effective at discriminating colors between 400 and 600nm. Vieyra (2011) found that there are a reduced number of functional olfactory genes in aquatic turtles. Vievra reported that sight moreso than odor was what attracted young turtles to food.
River cooter turtles typically are very secretive and tend to withdraw from anything that may appear as alarming to them. Specifically, these turtles tend to retreat quickly when confronted with sudden movements or loud noises. Generally, the auditory systems of aquatic turtles are not finely tuned but meet the turtles’ basic hearing needs.
Though secretive, river cooter turtles do interact quite often with each other. They are known to remain in the water except to participate in basking and nesting, and commonly perform these activities in groups. When breeding, male turtles use vision and tactile senses as they swim slightly above female turtles and use their claws to grab the female turtles’ faces and shells. Additionally, male turtles occasionally swim behind females and bite at the edge of the females’ shells to signal their mating interest. (Arnold and Neumeyer, 1987; Bartlett and Bartlett, 1996; Dreslik, 1996; Ernst and Lovich, 2009; Lavender, et al., 2014; Noble and Breslau, 1937; Vieyra, 2011)
River cooter turtles are predominantly herbivorous, feeding primarily on aquatic vegetation. While both adult and juvenile river cooters occasionally consume crayfish (e.g., Cambarus batchi, bluegrass crayfish) and other animal prey, juveniles do so more than adults. Apart from this, the dietary habits of juveniles and mature adults tend to be quite similar. These turtles commonly consume eelgrass (Zostera), green algae (Pediastrum boryanum), pondweeds (Potamogeton), and other aquatic macrophytes. (Buhlmann and Vaughan, 1991; Dreslik, 1996; Dreslik, 1997; Dreslik, 1999; Ernst and Lovich, 2009; Lagueux, et al., 1995; Van Dijk, 2016)
River cooter turtles are the prey of animals such as raccoons (Procyon lotor), Virginia opossums (Didelphis virginiana), red foxes (Vulpes vulpes), river otters (Lontra canadensis), and American crows (Corvus brachyrhynchos). In order to protect themselves from these predators, the turtles use their shells as a protective covering, and often recede into them when predators are near. As well as this, the color of these turtles enables them to blend into their surroundings and therefore avoid predatory attacks. (Stacy, et al., 2014; Van Dijk, 2016)
Many parasites that live in the liver and kidneys of river cooter turtles are relatively harmless to the overall health of these turtles, but a few can be detrimental. In these severe cases, humans need to be exceptionally careful in determining treatment, because many treatments that are effective in other animals are fatal when used in turtles. In a study by Silvestre et al. (2015), parasites were detected in 27/70 turtles examined. In this study, the nematodes Serpinema microcephalus and Serpinema trispinosum infected the turtles. Total worm counts within the turtles ranged from 5 to 21. (Silvestre, et al., 2015; Ward and Dale, 2008)
River cooter turtles are occasionally consumed as food and traded as pets. Their meat, eggs, and skin can be sold as commodities and used to make products for human consumption. (Van Dijk, 2016)
River cooter turtles have no known negative economic impacts on humans.
In 2001, IUCN Red List classified river cooter turtles as G5, or a species of “Least Concern.” The conservation status of river cooters is not listed on the Convention on International Trade in Endangered Species of Wild Fauna or Flora (CITES) or the United States Endangered Species Act (US ESA). Although they are not a species of high concern globally, these turtles are endangered in Illinois, and a species of special concern in Florida.
The biggest threats to these turtles result from human interference, such as illegal hunting, road-mortality, pollution, and habitat alterations (impoundments, changing shading for nesting spots). Currently, the only protection for these turtles is provided though general game and wildlife regulations, which lack specificity to river cooter turtles. The exception to this is in Florida, where the harvest of the species is restricted, because the species is of special concern. One road in Florida, a source of substantial mortality events, was modified to allow safe passage of these turtles. Although no additional conservation proposals address this particular species, general land and river protection efforts protect areas inhibited by this species. (Ernst and Lovich, 2009; Van Dijk, 2016; Ward and Dale, 2008)
Madeline Malueg (author), Radford University, Karen Powers (editor), Radford University, Alex Atwood (editor), Radford University, Marisa Dameron (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
mainly lives in water that is not salty.
An animal that eats mainly plants or parts of plants.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
Animals with indeterminate growth continue to grow throughout their lives.
referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
seaweed. Algae that are large and photosynthetic.
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
the business of buying and selling animals for people to keep in their homes as pets.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
Living on the ground.
uses sight to communicate
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