The bog turtle (Glyptemys muhlenbergii), also known commonly as Muhlenberg's turtle, is a critically endangered species of semiaquatic turtle in the family Emydidae. The species is native to the eastern United States. It was first scientifically described in 1801 after an 18th-century survey of Pennsylvania. The smallest North American turtle, it measures about in straight carapace length when fully grown. Although the bog turtle is similar in appearance to the painted turtle (Chrysemys picta) and the spotted turtle (Clemmys guttata), its closest relative is actually the somewhat larger wood turtle (Glyptemys insculpta). The bog turtle can be found from Vermont in the north, south to Georgia, and west to Pennsylvania. Diurnal and secretive, it spends most of its time buried in mud and – during the winter months – in hibernation. The bog turtle is omnivorous, feeding mainly on small invertebrates. The bog turtle is the state reptile of New Jersey.
An adult bog turtle weighs on average. Its skin and shell are typically dark brown, with a distinctive orange spot on each side of the neck. Considered threatened at the federal level, the bog turtle is protected under the United States' Endangered Species Act. Invasive plants and urban development have eradicated much of the bog turtle's habitat, substantially reducing its numbers. Demand for the bog turtle is high in the black market pet trade, partly because of its small size and unique characteristics. Various private projects have been undertaken in an attempt to reverse the decline in the turtle's population.
The bog turtle has a low reproduction rate; females lay one clutch per year, with an average of three eggs each. The young tend to grow rapidly, reaching sexual maturity between the ages of 4 and 10 years. Bog turtles live for an average of 20 to 30 years in the wild. Since 1973, the Bronx Zoo has successfully bred the bog turtle in captivity.
Taxonomy
The bog turtle was noted in the 18th century by Gotthilf Heinrich Ernst Muhlenberg, a self-taught botanist and clergyman. Muhlenberg, who named more than 150 North American plant species, was conducting a survey of the flora of Lancaster County, Pennsylvania, when he discovered the small turtle. In 1801, Johann David Schoepff named Muhlenberg's discovery Testudo muhlenbergii in Muhlenberg's honor.Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. . (Glyptemys muhlenbergii, p. 184).
In 1829, Richard Harlan renamed the turtle Emys muhlenbergii. The species was subsequently renamed Calemys muhlenbergii by Louis Agassiz in 1857, and Clemmys muhlenbergii by Henry Watson Fowler in 1906. Synonyms include Emys biguttata, named in 1824 by Thomas Say on the basis of a turtle from the vicinity of Philadelphia, and Clemmys nuchalis, described by Dunn in 1917 from near Linville, North Carolina. Today, there are various names for the bog turtle, including mud turtle, marsh turtle, yellowhead, and snapper (not to be confused with the snapping turtle, which often goes by the same name).
The genus name was changed to Glyptemys in 2001. The bog turtle and the wood turtle, Glyptemys insculpta, had until then been included in the genus Clemmys, which also included the spotted turtle (C. guttata) and the western pond turtles (C. marmorata). Nucleotide sequencing and ribosomal DNA analyses suggested that the bog turtle and the wood turtle are closely related, but neither is directly related to the spotted turtle, hence the separation of the genus Glyptemys.
Description
The bog turtle is the smallest species of turtle in North America. The adults weigh approximately when fully grown. It does not have a prominent snout. Its head is dark brown to black, and it has a bright yellow, orange, or red spot on each side of its neck. The spot is often forked, facing posteriorly. The bog turtle has a dark skin color with an orange-red wash on the inside of the legs of some individuals. The carapace is domed and rectangular in shape, and it tends to be narrower toward the head and wider toward the tail. The carapace often has easily identifiable rings on the rough scales or scutes. The scutes may also have a radiating arrangement of lines. In some older individuals, and those that burrow frequently in coarse substrates, the shell may be smooth. Although generally black, a chestnut sunburst pattern in each scute is sometimes present on the carapace. The belly of the shell, the plastron, is also a dark brown to black color with light marks present.
The spotted turtle and painted turtle are similar in appearance to the bog turtle. The bog turtle is distinguishable from any other species of turtle in its geographic range by the distinctively colored blotch on its neck. A major difference between it and the spotted turtle is that the bog turtle has no coloration on the upper shell, unlike the latter species.
Mature male bog turtles have an average length of (straight carapace measurement), while the average female length is . The males have a larger average body size than females, likely due to sexual selection for larger males in winning and performing the act of mating. The female has a wider and higher shell than the male, but the male's head is squared and larger than a female's of the same age. The plastron of the male looks slightly concave while the female's is flat. The male's tail is longer and thicker than the female's. The cloaca is further towards the end of the tail of the male bog turtle, while the female's cloaca is positioned inside the plastron. Juveniles are very difficult to sex.
Geographic distribution and habitat The bog turtle is native only to the eastern United States, congregating in colonies that often consist of fewer than 20 individuals. It prefers calcareous wetlands (areas containing lime), including meadows, bogs, marshes, and spring seeps, that have both wet and dry regions. Its habitat is often on the edge of woods. The bog turtle has sometimes been seen in cow pastures and near beaver dams. With habitats often time containing both overlapping wet and dry pockets
The bog turtle's preferred habitat, sometimes called a fen, is slightly acidic with a high water table year-round. The constant saturation leads to the depletion of oxygen, subsequently resulting in anaerobic conditions. Soft mud, sand, or stone characterize the bottom substrate. The bog turtle uses soft, deep mud to shelter from predators and the weather. Spring seeps and groundwater springs provide optimum locations for hibernation during winter. Home range size is sex dependent, averaging about for males and for females. However, research has shown that densities can range from 5 to 125 individuals per . The range of the bog turtle extensively overlaps that of its relative, the wood turtle.
Rushes, tussock sedge, cattails, jewelweed, sphagnum, and various native true grasses are found in the bog turtle's habitat, as well as some shrubs and trees such as willows, red maples, and alders. It is important for its habitat to have an open canopy, because the bog turtle spends a considerable amount of time basking in the sunlight. An open canopy allows sufficient sunlight to reach the ground so that the bog turtle can manage its metabolic processes through thermoregulation. The incubation of eggs also requires levels of sunlight and humidity that shaded areas typically lack. The ideal bog turtle habitat is early successional. Late successional habitats contain taller trees that block the necessary sunlight. Erosion and runoff of nutrients into the wetlands accelerate succession. Changes caused by humans have begun to eliminate bog turtles from areas where they would normally survive.
Northern and southern populations
The northern and southern bog turtle populations are separated by a gap over much of Virginia, which lacks bog turtle colonies. In both areas, the bog turtle colonies tend to occupy widely scattered ranges.
The northern population is the larger of the two. These individuals make their home in states as far north as Connecticut and Massachusetts, and as far south as Maryland. These turtles are known to have fewer than 200 habitable sites left, a number that is decreasing.
The southern population is much smaller in number (only about 96 colonies have been located), living in the states of North Carolina, South Carolina, Georgia, Virginia, and Tennessee. This area in particular has seen about 90 percent of its mountainous wetlands dry up. The turtles in this population are even more scattered than in the northern population and live at higher elevations, up to .
Evolutionary history There have been only three recorded discoveries of bog turtle fossils. The late J. Alan Holman, a paleontologist and herpetologist, first identified bog turtle plastral remains in Cumberland Cave, Maryland (near Corriganville), which are of Irvingtonian age (from to 300,000 years ago). The second discovery was of Rancholabrean (between 300,000 and 11,000 years ago) shell pieces in the Giant Cement Quarry in South Carolina (near Harleyville), by Bentely and Knight in 1998. The third discovery was found in Livingston County, New York, at the Cole Gravel Pit archaeological site (around 3900 years ago).
The bog turtle's karyotype is composed of 50 chromosomes. Studies of variations in mitochondrial DNA indicate low levels of genetic divergence among bog turtle colonies. This is unusual in species such as the bog turtle, which have fragmented distributions and exist in small isolated groups (fewer than 50 individuals in bog turtle colonies). These conditions limit gene flow, typically leading to divergence between isolated groups. Data indicate that the bog turtle suffered dramatic reductions in numbers – a population bottleneck – as colonies were forced south in the face of glaciation. Receding glaciers led to the relatively recent post-Pleistocene expansion, as the bog turtles moved back into their former northern range. This recent colonization from a relatively limited southern population may account for the reduction of genetic diversity. The northern and southern populations are at present genetically isolated, likely as a consequence of farming and habitat destruction in Virginia's Shenandoah Valley during the American Civil War.
Ecology and behavior
Behavior The bog turtle is primarily diurnal, active during the day and sleeping at night. It wakes in the early morning, basks until fully warm, then begins its search for food. It is a seclusive species, making it challenging to observe in its natural habitat. During colder days, the bog turtle will spend much of its time in dense underbrush, underwater, or buried in mud. Such behavior is indicative of the bog turtle's ability to survive without oxygen. On warmer days, the bog turtle's activities include scavenging, mating (during early spring), and basking in sunlight, the last of which it spends a great deal of the day doing. However, the bog turtle usually takes shelter from the sun during the hottest part of the day. Occasionally, during times of extreme heat, the turtle will either estivate, or become subterranean, sometimes occupying networks of tunnels filled with water. At night, the bog turtle buries itself in soft tunnels.
Late September to March or April is usually spent in hibernation, either alone or in small groups in spring seeps. These groups can contain up to 12 individuals, and sometimes can include other species of turtles. Bog turtles try to find an area of dense soil, such as a strong root system, for protection during the dormant period. However, they may hibernate in other places such as the bottom of a tree, animal burrows, or empty spaces in mud. The bog turtle emerges from hibernation when the air temperature is between .