Eastern mud turtles (Kinosternon subrubrum) are native to the Neartic region and range along the southeastern United States. Their range extends westwards towards east-central Texas along the southern Gulf Coast. Mud turtles are found as far north as the tip of Long Island, New York, and the range continues south of Virginia, east of the Blue Ridge Mountains. They inhabit the eastern two-thirds of North Carolina, southwestern third of Tennessee, southwestern half of Kentucky, and eastern third of Oklahoma. Southward, their range encompasses almost all of Arkansas, the southwest portion of South Carolina, and the entirety of Georgia, Alabama, Mississippi, Florida, and Louisiana. There are two disjunct populations: one in northwest Indiana and another in west-central Missouri.
Eastern mud turtles are freshwater turtles and are weak swimmers that dive to depths of one to three meters. These turtles inhabit still, shallow waters such as ponds, lagoons, marshes, cypress swamps, and bayous. They can also inhabit brackish water, and moving water, like streams and rivers, that contain aquatic vegetation. They hardly bask, but when they do it is on rocks or debris floating on the water’s surface. Eastern mud turtles have a minimum elevation of 0 m at sea level and the maximum elevation has not yet been reported. These turtles also overwinter in terrestrial habitats by burrowing. They tend to burrow at wetland wedges at a minimum depth of 1.3 cm below the soil surface to a maximum depth of 3 cm, depending on the season. (Buhlmann, et al., 2008; Cordero, et al., 2012; Ernest and Barbour, 1989; Ernst and Lovich, 2009; Minton Jr., 2012)
Eastern mud turtles have two plastral hinges that sit up against their oval-shaped carapace. Their carapace can be solid brown, olive with irregular streaks of yellow, or solid black. Their limbs usually have smudged patterns that are grey, brown, or occasionally black. Their heads have markings and irregular stripes that can be jagged. These markings and irregular stripes can also lie between the eyes and nostrils. Both sexes display the same color patterns and markings. Eastern mud turtles also display tails tipped with spines and notches on the posterior portion of their plastrons. Eastern mud turtles are distinguishable amongst other similar species by their geographical location and irregular stripes or markings, mottling, and smudged patterns.
These turtles exhibit sexual dimorphism, as males are smaller than females. Adult males have an average size of 93.7 mm (range 78.2-108.5 mm) carapace length (CL) and an average mass of 157.3 g (range 88-206 g). Female average size is 92.8 mm (range 75.7-123.0 mm) CL, and their average body mass is 164.7 g (range 100-263 g). Additional differences between the sexes reflect further dimorphism. Males have longer tails, larger heads, a patch of raised scales along their hindlegs, and deeper posterior plastral notches. Juvenile skin is black, and their heads occasionally have light stripes. The carapace of juveniles has three keels and a plastron that can be orange, yellow, or red with blotches of black. Juveniles range from 2.0-2.5 mm CL, and their body mass ranges from 2.3-3.4 g. (Buhlmann, et al., 2008; Ernst and Lovich, 2009; Mitchell, 1994)
The eggs of eastern mud turtles are typically pinkish and blueish-white while the shells are brittle and elliptical. Eastern mud turtles exhibit temperature-dependent sex determination. Males are produced at an incubation temperature range of 21.5 to 27 degrees Celsius. A mix of males and females are produced at an incubation temperature range from 27.0 to 30.0 degrees Celsius. Females are produced at an incubation temperature of at and above 30 degrees Celsius. The eggs range 16.7 to 32.3 mm in length and 12.7 to 20.0 mm in width. The eggs weigh 3.0 to 4.9 grams. Eastern mud turtles exhibit indeterminate growth as they continue growing even after adulthood. Hatchlings are similar in shape to adults as they possess the same carapace shape but present vertebral keels (unlike adults). The plastrons of hatchlings are mottled with orange, yellow, or red blotches with black. Hatchlings' skin is black while adults’ skin tends to be brown or a greyish tone. Both females and males reach sexual maturity at a carapace length of 8 cm.
Juvenile females' growth rates vary depending on location, as temperature plays a role. Mahmoud (1969) reported that in Oklahoma, limited to its warmer months, females’ carapace lengths increased by an average of 16.6 mm per year. The initial carapace length ranged from 21 to 40 mm, but female turtles that were above average had different growth rates per growing season. Those that initially ranged 41 to 60 mm increased 13.7 mm in CL, 61 to 80 mm increased by 2.6 mm CL, and the females that measured 80 mm or greater increased by 0.38 mm CL.
In South Carolina’s warmer months, Gibbons (1983) reported both males’ and females’ carapace lengths grow to 70 to 80 mm in four to six years. Males with initial carapace lengths from 61 to 80 mm increased 3.0 mm per year. Males of carapace length >81mm increased by 0.83 mm per year. Both males and females showed CL increases in the first six years until growth rates leveled out or slowed down. (Ernst and Lovich, 2009; Mitchell, 1994; Whitfield Gibbons, 1983)
Eastern mud turtles are polygynandrous and their mating period is from mid-March to May. These turtles typically mate underwater but mating also occurs on land. Mating is initiated when females’ musk glands secrete pheromones when they are ready to mate. Males will detect the scent of these pheromones and attempt mating.
Males assert themselves by mounting females and biting their heads and carapaces. Males utilize their necks to feel the tail of the female they are attempting to court and to nudge against the female’s bridge area to make direct contact with her musk glands. (Ernest and Barbour, 1989; Ernst and Lovich, 2009; Mahmoud, 1967; Mason, 1992; Mitchell, 1994)
Eastern mud turtles mate each year from mid-March through May. Eastern mud turtles breed for 2 months, reproduce sexually, and are oviparous. Egg-laying depends on the geographical region as the nesting period is shorter in northern populations. Typically nesting takes place from May to June, but some of the northern populations nest from April to July. The incubation period is approximately 100 days from when the females lay their clutch. Females can dig a couple of times before determining where the will lay their eggs. The nest is typically dug with their forefeet on open ground close to a body of water in a semicircle cavity ranging from about 7.5 to 13 cm deep. Once the females have laid their eggs, they use their hindfeet to conceal the eggs by packing soil directly over and around them.
Most eggs hatch from late August to September, but this can vary by the timing of egg-laying. The average clutch is two to four eggs, but there can be as many as nine eggs. Birth mass is not typically recorded for turtles, but the average carapace length of hatchings ranges from 16.6 to 27.0 mm.
Hatchlings reach independence immediately as they are left by the females once the eggs are laid. Males sexually mature at a low of three years and high of seven years with an average of four years. Females sexually mature at a low of three years and a high of eight years with an average of five years. Maturity is linked to carapace length, as both females and males typically mature at a length of 8 cm. In some studies, the reported range at maturity is 8 to 12 cm. (Buhlmann, et al., 2008; Ernest and Barbour, 1989; Ernst and Lovich, 2009; Mitchell, 1994)
Females may begin nests in several locations to test them out before fully committing to digging and laying their eggs. This ensures the highest survival rate for their hatchlings. The nest is typically dug on open ground close to a body of water in a semicircle cavity ranging from about 7.5 to 13 cm deep. Females utilize their forefeet to dig the nest and hindlegs to pack soil directly over and around the eggs. Males provide no parental investment beyond the act of mating, and females provide no parental investment beyond the act of egg-laying and nest creation.
The longest known lifespan of eastern mud turtles is unknown. Frazer et al. (1991) estimate that their lifespan ranges from 20 to 50 years in the wild or captivity. Frazer et al. further reported that a female eastern mud turtle lived 38 years in captivity.
Mortality is highest in the egg stage, as they are consumed by predators. Frazer et al. (1991) found that adult female eastern mud turtles exhibit an annual survival rate of 87.6 percent, while adult males exhibit a rate of 89 percent. (Frazer, et al., 1991)
Eastern mud turtles are natatorial and solitary. They hibernate between November and March, but start and stop times vary by location. These turtles’ hibernaculum includes shallow burrows at the edge of wetlands. Eastern mud turtles are crepuscular. Depending on ambient temperature, they spend their time either submerged in shallow waters or basking in the sun at the water’s surface. These turtles can bask with conspecifics on the same log, but this occurs mostly during mating season. These turtles are occasionally aggressive and fight each other with head-to-head-confrontation. Such confrontations can lead to potential severe injuries such as severed limbs, but the reason for aggression is unknown. Eastern mud turtles use the perception of color to distinguish sexes, which plays a role in courting. When mating, females’ musk glands release pheromones to signal the males to begin the act of courtship. Females dig their nests and conceal their nest by utilizing their forefeet and hindlegs, and then they lay their clutch. (Buhlmann, et al., 2008; Cooper JR. and Greenberg, 1992; Ernest and Barbour, 1989; Ernst and Lovich, 2009; Mason, 1992; Mitchell, 1994)
Eastern mud turtles may have to travel long distances due to terrestrial environmental factors such as droughts and to keep their aquatic movement constant . Swarth et al. (2012) investigated home ranges in these turtles, often measured in stream (linear) distances as well as area. They reported linear movements maxing out at 887 m in 2008 and 903m in 2009. Areal home ranges were reported as 18.6 ha in 2008 and 16.3 ha in 2009. Error ranges for both linear and areal averages were substantial, suggesting a great deal of movement variability among individuals. There was a difference between males and females in both linear and areal movements. Males’ linear movements maxed out at 402 m in 2008 and 286 m in 2009, and areal home ranges were 30.1 ha in 2008 and 26.5 ha in 2009. Females’ linear movements maxed out at 205 m in 2008 and 327m in 2009, while areal home ranges were 4.9 ha in 2008 and 7.7 ha in 2009. Eastern mud turtles do not defend a territory. (Swarth, et al., 2012)
Eastern mud turtles use tactile senses and vision when they are foraging. They use vision to seek out their prey and tactile senses for the actual consumption of the prey. Both sexes utilize tactile senses when they are digging their holes for burrowing. Only females use tactical senses for digging nests to lay their eggs.
Eastern mud turtles communicate by the secretion of pheromones; the musk glands of females release them as part of courtship behaviors. When the females secrete these pheromones, they are signaling their location and receptivity to the males. Courtship often includes both tactile and visual perception and communication. Males utilize their necks to feel the tail of whom they are attempting to court to distinguish female from male. Males also then use their necks to rub against the female’s bridge area to be able to smell the pheromones being secreted by the musk glands. The perception of color plays a role in communication, as the turtles use bright colors to distinguish sexual selection and temporal stability.
Eastern mud turtles are omnivores and have a broad dietary range. They are mostly bottom feeders consuming primarily in water, but sometimes come up to surface level if the opportunity presents itself. Their range of consumption includes seeds, small invertebrates such as earthworms (family Lumbricidae) and snails (Lymnaea, Physa, Planorbis), small insects such as moths and butterflies (order Lepidoptera ), June beetles (order Coleoptera, family Scarabaeidae, subfamily Melolonthinae), as well as arachnids (order Araneae), green algae, crustaceans, and carrion. Strecker (1927) reported that these turtles also consumed one small lined snake (Tropidoclonion lineatum).
Mahmound (1967) investigated the diet of eastern mud turtles in North Carolina based off the frequency of each food item found in the stomach. He found that mud turtles consumed crustaceans (15%), amphibians (30%), carrion (68.6%), molluscs (93%), insects (98.3%), and aquatic vegetation (89.6%). Mahmound (1967) further suggested that juveniles’ diets are the same as the adults.
Juvenile eastern mud turtles are susceptible to wetland predators such as blue crabs (Callinectes sapidus), water snakes (Nerodia), and cottonmouths (Agkistrodon piscivorus) due to their small size. Adult eastern mud turtles’ predators include Virginia opossums (Didelphis virginiana), weasels (Mustela), raccoons (Procyon lotor), gray foxes (Urocyon cinereoargenteus), kingsnakes (Lampropeltis), bald eagles (Haliaeetus leucocephalus), and red imported fire ants (Solenopsis invicta). Nest predation occurs by shrews (family Soricidae) and mostly mid-sized carnivorous mammals such as raccoons, skunks (family Mephitidae), and foxes (gray foxes, red foxes Vulpes vulpes). Eastern mud turtles can live up to 30 years or longer and employ two defensive mechanisms: completely hiding in their protective shells and forcefully biting their predators. (Buhlmann, et al., 2008; Ernst and Lovich, 2009)
Eastern mud turtles play their role in the food chain as they are prey for several mid-sized carnivorous mammalian predators. Predators include a variety of mid-sized mesocarnivores. Eastern mud turtles have a broad dietary range as they consume seeds, small aquatic insects, other invertebrates, and carrion. Eastern mud turtles are hosts for parasites including roundworms (phylum Nematoda), flukes (class Trematoda), tapeworms (class Cestoda, Cercorchis), and smooth turtle leeches (Placobdella parasitica). (Byrd, 1963; Mayberry, et al., 2000; McCoy, et al., 2007)
Eastern mud turtles can serve as pets, a positive economic impact on humans. Eastern mud turtles can cost $10 to $50 dollars, but are also sold in the illegal pet trade. (Shiau, et al., 2006)
In captivity, eastern mud turtles can spread salmonella to humans. They do not transmit it in the wild. These turtles do carry other bacteria such as Citrobacter, Enterobacter, Escherichia coli, Hafnia, Klebsiella, and Proteus. (Mitchell and McAvoy, 1990)
Eastern mud turtles are classified as a species of “Least Concern” according to IUCN Red List. They are not listed on the US Federal List, CITES, and the state of Michigan List. Eastern mud turtles are considered state-endangered in Indiana, New York, and Pennsylvania, and a species of greatest conservation need in Kentucky (Meshaka et al. 2017).
The main threat to these turtles is habitat loss and highway mortality, as few turtles manage to cross highways. Habitat loss via roads bisecting aquatic habitats, increased urbanization, and a change in climate that elevates sea levels all harm these mud turtles. Illegal pet trade of this species also has caused damage to their native ecosystem via loss of biodiversity.
Possible conservation efforts to decrease mortality rates include wetland legislation that protects a terrestrial buffer zone around these semi-aquatic habitats. These terrestrial buffers are already intact in national parks. A better understanding of population changes over time as well as their perceived response to broad climatic change and microhabitat change is necessary for future conservation efforts (Meshaka et al. 2017). (Meshaka, et al., 2017)
Bianca Plowman (author), Radford University, Karen Powers (editor), Radford University, Victoria Raulerson (editor), Radford University, Christopher Wozniak (editor), Radford University, Genevieve Barnett (editor), Colorado State University.
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.
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.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
flesh of dead animals.
uses smells or other chemicals to communicate
active at dawn and dusk
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
Referring to a burrowing life-style or behavior, specialized for digging or burrowing.
mainly lives in water that is not salty.
An animal that eats mainly plants or parts of plants.
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.
An animal that eats mainly insects or spiders.
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).
marshes are wetland areas often dominated by grasses and reeds.
eats mollusks, members of Phylum Mollusca
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.
an animal that mainly eats all kinds of things, including plants and animals
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.
chemicals released into air or water that are detected by and responded to by other animals of the same species
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
an animal that mainly eats dead animals
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
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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