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Graptemys nigrinodaBlack-knobbed Map Turtle

By Matt Shuma

Geographic Range

Black-knobbed map turtles (Graptemys nigrinoda) are native to the Nearctic region. They reside in northeastern Alabama and from central to western Mississippi, on the northern stretches of the Tombigbee-Black Warrior, Tallapoosa, Coosa, and Cahaba Rivers. While these rivers flow into the Gulf of Mexico, the range of black-knobbed map turtles does not extend into the Gulf. (Bartlett and Bartlett, 2006; Ernst and Barbour, 1972; Harless and Morlock, 1979)

Habitat

Black-knobbed map turtles live strictly in aquatic areas. This is because they suffer high rates of evaporative water loss compared to other terrestrial turtles. They commonly reside in river systems with shallow to deeper channels of water. Black-knobbed map turtles are most commonly found in sand and clay substrates of rivers, with a moderate to strong river current. When out of water, these turtles bask on brush, exposed trees, and rafted plants to acquire direct sunlight.

While their overall habitat choice stays consistent, there is some microclimate variation between age groups. Younger black-knobbed turtles are observed across a wider range of aquatic habitats, especially basking sites. Older turtles are most commonly observed at the middle course of the river while juveniles are sighted at lower courses, in more shallow waters. These turtles can dive up to three meters deep. (Bartlett and Bartlett, 2006; Folkerts and Mount, 1969; Guyer, et al., 2015; Harless and Morlock, 1979; Killebrew, 1979)

  • Aquatic Biomes
  • rivers and streams
  • Range depth
    0 to 3 m
    0.00 to 9.84 ft

Physical Description

Black-knobbed map turtles received their name from the circular knobs with lines surrounding them that protrude from their carapace. Females have an average carapace size of 152 to 178 mm and a total length of 221 mm. Males have an average carapace size of 76 to 102 mm and a total length of 122 mm. While females are larger in size, males have relatively larger, thicker tails. A distinguishing feature is the black vertical knobs on their outer scutes. Their heads, legs, and tails are brownish in color and lined with yellow stripes, which are identical in both males and females; this is common in North American turtles, since they serve as camouflage in vegetated wetlands. Their undersurface is lighter when compared to the dorsum. These colored features are most prominent on young turtles.

Eggs, on average, measure 38.8 mm by 22.7 mm. The average mass of eggs is 11.8 g. The weight of new hatchlings, on average, is 8.9 g, with a carapace length of 35.5 mm.

Black-knobbed map turtles share characteristics between other turtles in the genus Graptemys, such as Alabama map turtles (Graptemys pulchra), Escambia map turtles (Graptemys ernsti), Pascaloula map turtles (Graptemys gibbonsi), and Barbour's map turtles (Graptemys barbouri). Characteristics that distinguish black-knobbed map turtles from other species include: lighter pigmentation, softer tissues, a ridged shell shape, and smaller carapace sizes. Subspecies of Graptemys nigrinoda include G. n. delticola and G. n. nigrinoda. The subspecies G. n. delticola is distinguished by its darker pigmentation, larger carapace size, and recurved postorbital blotches. The subspecies G. n. nigrinoda possesses light colored soft spots, a dark plastral pattern, and a crescent shaped postorbital mark. (Bartlett and Bartlett, 2006; Blankenship, et al., 2008; Carr, 1952; Ennen, et al., 2014; Gibbons and Greene, 2009; Lahanas, 1986; van Dijk, 2016)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    76 to 178 mm
    2.99 to 7.01 in

Development

Black-knobbed map turtles lay eggs with average dimensions of 38.8 mm by 22.7 mm. The average mass of eggs is 11.8 g. Newly hatched turtles weigh, on average, 8.9g and have a carapace length of 35.5 mm.

Black-knobbed map turtles display sexual bimaturism; males take two to three years to mature while females take 8 to 9 years to mature. Turtles do not undergo metamorphosis. As turtles grow from hatchlings into adults, their shells grow with them. As turtles and their shells grow, older scutes on the shell will peel and shed away. Turtles display indeterminate growth, meaning they grow throughout their life.

There is a phenomenon within turtles called temperature sex determination, where the sex is determined based on the temperature at which eggs are kept. At temperatures of 31°C or above, hatchlings are primarily female; and at temperatures of 25°C or below, hatchlings are primarily male. Temperatures between 25 and 31°C produce a mixture of both sexes. (Bartlett and Bartlett, 2006; Gibbons and Greene, 2009; Lindeman, 2008; Lindeman, 2016; Lovich, et al., 2009; Pluto and Bellis, 1988; Vogt and Bull, 1982)

Reproduction

Black-knobbed map turtles mate seasonally, beginning between late winter and early spring, when the temperature starts to rise. Males seek out females and then engage in courtship activities. Male black-knobbed map turtles employ a courtship method called titillation, in which they extend a specially adapted elongated foreclaw and vibrate it in the water in front of females. When females are receptive to mating, they follow males as they swim backwards. Males then mount the carapaces of females, their tails curl together, and males inseminate females. Both sexes produce grunting noises during intercourse. These turtles are polygynandrous, which means both sexes mate with multiple partners throughout their life. Uncommonly, male-to-male aggressive behavior over a female turtle occurs during mating season. (Carr, 1952; Ernst and Barbour, 1972; Killebrew, 1979; Lindeman and Sharkey, 2001)

Black-knobbed map turtles lay eggs that are white or cream colored. Females lay 2 to 4 clutches of eggs between March and August. Clutch sizes range from 3 to 7 eggs (5.5 on average). Larger females produce more eggs. Black-knobbed map turtles dig nests on sandbars and lay their eggs at the mouths of these nests. Although they lay eggs nocturnally, females choose nesting sites in areas that are in direct sunlight to preserve the moisture in eggs and keep the soil warm. To find an adequate nesting spot with favorable features, turtles may travel long distances along river banks. Incubation periods range from 60 to 68 days. Recorded birth masses of these map turtles is between 8 to 14 grams. Black-knobbed map turtles are independent upon hatching.

These turtles are iteroparous – they mate multiple times throughout their lives. Across the species, males typically mature after 2 to 3 years, while females mature in 6 to 7 years. In the subspecies Graptemys nigrinoda delticola, males reach sexual maturity after 3 to 4 years of age with a carapace size of 70 mm. Females reach sexual maturity after 8 to 9 years with a carapace length of 170 mm. (Bartlett and Bartlett, 2006; Gibbons and Greene, 2009; Lindeman, 2008; Lindeman, 2016)

  • Breeding interval
    Black-knobbed map turtles breed once yearly.
  • Breeding season
    Black-knobbed map turtles breed between March and November
  • Range number of offspring
    3 to 7
  • Average number of offspring
    5.5
  • Range time to independence
    0 to 0 minutes
  • Range age at sexual or reproductive maturity (female)
    6 to 9 years
  • Range age at sexual or reproductive maturity (male)
    2 to 4 years

Black-knobbed map turtles exhibit minimal parental investment. Females invest time and energy by digging nests and carrying eggs until they are laid. After females are finished gestating eggs and digging nests, they leave. These unprotected eggs are susceptible to various predators as food. Upon hatching, young are independent immediately. Males provide no parental care beyond the act of mating. (Carr, 1952; Congdon, et al., 1983)

Lifespan/Longevity

Captive black-knobbed map turtles have a maximum lifespan of 20.3 years. While a maximum lifespan for individuals in the wild has not been recorded, another member of their genus, northern map turtles (Graptemys geographica), can live more than 20 years in the wild. Estimations of black-knobbed map turtle longevity suggest that females live longer than males in the wild. Lifespans are limited primarily by predation. (Lindeman, 2016; Vogt, 1993; Vogt and Bull, 1982)

  • Typical lifespan
    Status: captivity
    20.3 (high) years

Behavior

Black-knobbed map turtles are a solitary, fairly sedentary species. They have been observed to stay in place and alternate from basking on surfaces in the sun to being in the river. Juveniles are poor swimmers, but swimming speeds and diving depths increase as they mature. There are two periods throughout the day - mid-morning and early afternoon - where these turtles bask. They bask from early April through late November, when water temperatures are at or above 10°C. Basking in the sun helps turtles maintain a warm body temperature and also eliminates excessive algae from their shells. If turtles are disturbed, they will flee into the river.

With the exception of mating season, these turtles are generally not social during all stages of life. Male-on-male aggression has only been observed during mating season, or over basking sites. During aggressive encounters, turtles make grunting sounds. These grunting sounds are also made while these turtles mate. Another form of communication is used underwater at frequencies too low for humans to hear.

In general, black-knobbed map turtles can be found eating, basking, or mating. Northern map turtles (Graptemys geographica) have been observed hibernating between December through March, often in deeper waters with a slow current. Areas are also chosen where ice is less likely to form. It is likely that black-knobbed map turtles do something similar. (Carr, 1952; Jones, 1996; Lindeman, 2008; Lindeman, 2016; Pluto and Bellis, 1988; Shoop, 1967)

Home Range

Home ranges black-knobbed map turtles have not yet been reported. Conditions and habitat types likely influence the home range. Black-knobbed map turtles do not defend any territory. Yellow-blotched map turtles (Graptemys flavimaculata) have a reported home range of 1.5 km along a stretch of river. It is likely that black-knobbed map turtles have a similar range. (Carr, 1952; Gibbons and Greene, 2009; Harless and Morlock, 1979; Jones, 1996; Pluto and Bellis, 1988)

Communication and Perception

Black-knobbed map turtles communicate vocally through grunting sounds. These sounds are especially present during acts of aggression or while mating. These turtles are also able to communicate underwater at frequencies too low for humans to hear. They use a form of tactile communication in which males stroke the heads of females with an elongated claw. Males also have been reported rubbing their heads against females. These efforts signal female turtles to breed with communicating males. Other members in the genus Graptemys are phototactic upon hatching. This means they will move towards light sources after they have hatched. Anderson (1958) reported other members of the genus moving towards water upon hatching and always having water in their line of sight when nesting.

Like similar species, black-knobbed map turtles likely use visual and olfactory cues to recognize females. They likely also perceive sources of heat and vibrations in their environment. Vogt (1993) showed that male false map turtles (Graptemys pseudogeographica) use visual and olfactory cues, instead of tactile communication, to identify females; it is believed that black-knobbed map turtles do the same. (Anderson, 1958; Gibbons and Greene, 2009; Kardong, 2002; Vogt, 1993)

Food Habits

Black-knobbed map turtles are opportunistic omnivores, eating mollusks (Mollusca), crayfish (Astacoidea), and various aquatic vegetation. Three animal groups comprised more than 95% of the diet of black-knobbed map turtles: sponges (Porifera) and bryozoans (Bryozoa) for both sexes, plus green algae for males, and blue mussels (Mytilus edulis) for females (Lindeman, 2013). Lindeman (2016) reported that small-bodied turtles and adult males feed mostly on sponges while larger-bodied turtles and adult females feed on filamentous green algae.

Captive black-knobbed map turtles will eat ground beef, lettuce, raw liver, chopped fish, dog food, and commercial turtle food. These captive turtles also eat various invertebrates such as insects and worms.

Researching on a subspecies of map turtles, Graptemys nigrinoda delticola, showed that males had a diet consisting of 58.3% animal material and 40.4% plant material, while females had a diet of 69.2% animal material and 28.1% plant material. Reports of forging by Wahlquist (1970) found that turtles consumed beetles (Coleoptera) and dragonflies (Anisoptera) that fell into rivers. (Bartlett and Bartlett, 2006; Guyer, et al., 2015; Lindeman, 2008; Lindeman, 2013; Lindeman, 2016)

  • Animal Foods
  • fish
  • insects
  • mollusks
  • terrestrial worms
  • aquatic crustaceans
  • Plant Foods
  • leaves
  • algae

Predation

The most prominent anti-predator adaptations of black-knobbed map turtles is their coloration. The black and yellow stripes that line their limbs and heads, along with the distinctive black knobs on their shells, act as camouflage. This species also has long nails and will bite in order to defend itself.

The main predators of the black-knobbed map turtles are alligator gar (Atractosteus spatula), largemouth bass (Micropterus salmoides), raccoons (Procyon lotor), fish crows (Corvus ossifragus), nine-banded armadillos (Dasypus novemcinctus), red imported fire ants (Solenopsis invicta), American bullfrogs (Lithobates catesbeianus), and American alligators (Alligator mississippiensis).

These turtles are mostly preyed upon as eggs or as juveniles. The main predators of adults are humans, as they are sometimes used in cuisine. (Bartlett and Bartlett, 2006; Carr, 1952; Lindeman, 2008; Lindeman, 2016)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Black-knobbed map turtles are opportunistic omnivores, eating snails, clams, crayfish, aquatic insects, and aquatic vegetation. Eggs and hatchlings are preyed upon by herons, predatory fish, American alligators (Alligator mississippiensis) and some mammal species.

Black-knobbed map turtles are hosts for various blood flukes in Alabama. These parasites include: Spirorchis elegans, Spirorchis scripta, and Spirorchis paraminutus. (Bartlett and Bartlett, 2006; Carr, 1952; Lindeman, 2008; Lindeman and Barger, 2005; Roberts, et al., 2019)

Commensal/Parasitic Species
  • Blood fluke Spirorchis elegans
  • Blood fluke Spirorchis scripta
  • Blood fluke Spirorchis paraminutus

Economic Importance for Humans: Positive

Benefits that black-knobbed map turtles provide are for research and domestic purposes. Research is usually conducted through universities or by state agencies employing conservation efforts. These turtles are sometimes kept as pets and or collected locally as a source of food. (Killebrew, 1979; Lindeman, 2013; van Dijk, 2016)

  • Positive Impacts
  • pet trade
  • research and education

Economic Importance for Humans: Negative

There are no known negative economic impacts of black-knobbed map turtles on humans.

Conservation Status

Black-knobbed map turtles are considered a species of “Least Concern” on the IUCN Red List, as they have a stable population trend. They have no special status under the US Federal List or the State of Michigan's rare animal list. The state of Alabama has listed the species as a protected non-game animal, while the state of Mississippi has listed them as endangered. The state of Mississippi suggests conducting surveys to determine the range of black-knobbed map turtles, and to determine if reproduction is occurring. Under the Environmental Conservation Online System (ECOS), this species is "under review" to see if conservation efforts are needed. If determined to be at risk, coordination between the state of Alabama and other partners will gather information and suggest the best conservation efforts to take. CITES lists the species under Appendix III, which addresses the regulation of international trade. This regulation would require an export permit and certificate of origin from state officials.

Threats include removal from the wild for research or pet trades, removal of basking logs, drowning due to fishing gear, and boat strikes. Climate change is believed to alter patterns of seasonal activity due to warming waters and extreme weather events.

Conservation efforts include protected stretches of river to safeguard nesting sites. The Mobile Bay Aquatic Ecosystem Recovery Plan employs basic research and population monitoring to determine specific conservation measures to suggest. Outside of Mississippi, no conservation efforts have been suggested. (Blankenship, et al., 2008; "Endangered Species of Mississippi", 2014; Killebrew, 1979; Schlaepfer, et al., 2005; van Dijk, 2016; Vogt, 1993; Vogt and Bull, 1982)

Contributors

Matt Shuma (author), Radford University, Lauren Burroughs (editor), Radford University, Logan Platt (editor), Radford University, Karen Powers (editor), Radford University, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

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.

World Map

acoustic

uses sound to communicate

bilateral symmetry

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

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.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

freshwater

mainly lives in water that is not salty.

herbivore

An animal that eats mainly plants or parts of plants.

hibernation

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.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

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).

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Mississippi Department of Wildlife, Fisheries, and Parks. Endangered Species of Mississippi. None. Jackson, Mississippi: Mississippi Department of Wildlife, Fisheries, and Parks. 2014.

Anderson, P. 1958. The photic responses and water-approach behavior of hatchling turtles. Copeia, 1958/3: 211-215.

Bartlett, R., P. Bartlett. 2006. Guide and Reference to the Crocodilians, Turtles, and Lizards of Eastern and Central North America (North of Mexico). Gainesville, FL: University Press of Florida.

Blankenship, E., B. Butterfield, J. Godwin. 2008. Graptemys nigrinoda Cagle 1954- Black-knobbed map turtle, black-knobbed sawbuck. Conservation Biology of Freshwater Turtles and Tortoises: A Compilation Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group, 5: 005.1-005.6.

Carr, A. 1952. Handbook of Turtles. New York, NY: Comstock Publishing Associates.

Congdon, J., D. Tinkle, P. Rosen. 1983. Egg components and utilization during development in aquatic turtles. Copeia, 1983/1: 264-268.

Ennen, J., M. Kalis, A. Patterson, B. Kreiser, J. Lovich. 2014. Clinal variation of validation of a subspecies? A case study of the Graptemys nigrinoda complex (Testudines: Emydidae). Biological Journal of the Linnnean Society, 111/4: 810-822.

Ernst, C., R. Barbour. 1972. Turtles of the United States. Lexington, KY: The University Press of Kentucky.

Folkerts, G., R. Mount. 1969. A new subspecies of the turtle Graptemys nigrinoda Cagle. Copeia, 1969/4: 677-682.

Gibbons, W., J. Greene. 2009. Turtles: The Animal Answer Guide. Baltimore, MD: The John Hopkins University Press.

Guyer, C., M. Bailey, R. Mount. 2015. Turtles of Alabama. Tuscaloosa, AL: The University of Alabama Press.

Harless, M., H. Morlock. 1979. Turtles: Perspectives and Research. New York, NY: Wiley-Interscience.

Jones, R. 1996. Home range and seasonal movements of the turtle Graptemys flavimaculata. Journal of Herpetology, 30/3: 376-385.

Kardong, K. 2002. Vertebrates: Comparative Anatomy, Function, Evolution. New York, NY: McGraw-Hill Higher Education.

Killebrew, F. 1979. Osteological variation between Graptemys flavimaculata and Graptemys nigrinoda (Testudines: Emydidae). Herpetologica, 35/2: 146-153.

Lahanas, P. 1986. Graptemys nigrinoda Cagle - Black-knobbed sawback. Catalogue of American Amphibians and Reptiles, 396: 396.1-396.2.

Lindeman, P. 2013. The Map Turtle and Sawbuck Atlas: Ecology, Evolution, Distribution, and Conservation. Norman, Oklahoma: University of Oklahoma Press.

Lindeman, P. 2016. Diets of syntopic black-knobbed sawbucks (Graptemys nigrinoda) and Alabama map turtles (Graptemys pulchra) in the Alabama River. The American Midland Naturalist, 175/2: 194-205.

Lindeman, P. 2008. Evolution of body size in the map turtles and sawbacks (Emydidae: Deirochelyinae: Graptemys). Herpetologica, 64/1: 32-46.

Lindeman, P., M. Barger. 2005. Acanthocephalan (Neoechinorhynchus emydis) infections in Texas map turtles (Graptemys versa). The Southwestern Naturalist, 50/1: 12-16.

Lindeman, P., M. Sharkey. 2001. Comparative analyses of functional relationships in the evolution of trophic morphology in the map turtles (Emydidae: Graptemys). Herpetologica, 57/3: 313-318.

Lovich, J., W. Selman, C. McCoy. 2009. Chapter 29: Graptemys gibbonsi Lovich and McCoy 1992 – Pascagoula map turtle, Pearl River map turtle, Gibbons’ map turtle. Pp. 029.1-029.8 in A Rhodin, P Pritchard, P van Dijk, R Saumure, K Buhlmann, J Iverson, R Mittermeier, eds. Conservation Biology of Freshwater Turtles and Tortoises. Lunenburg, Massachusetts: Chelonian Research Foundation.

Pluto, T., E. Bellis. 1986. Habitat utilization by the turtle, Graptemys geographica, along a river. Journal of Herptology, 20/1: 22-31.

Pluto, T., E. Bellis. 1988. Seasonal and annual movements of riverine map turtles, Graptemys geographica. Journal of Herpetology, 22/2: 152-158.

Roberts, J., M. Warren, K. Halanych, S. Bullard. 2019. Spirorchis spp. (Digenea: Schistosomatoidea) infecting map turtles (Cryptodira: Emydidae: Graptemys spp.) in southeastern North America: A new species, molecular phylogenies, and key to species. Systematic Parasitology, 96/1: 51-64.

Schlaepfer, M., C. Hoover, K. Dodd. 2005. Challenges in evaluating the impact of the trade in amphibians and reptiles on wild populations. Bioscience, 55/3: 256-264.

Shoop, R. 1967. Graptemys nigrinoda in Mississippi. Herpetologica, 23/1: 57.

Vogt, R. 1993. Systematics of the false map turtles (Graptemys pseudogeographica complex: Reptillia, Testudines, Emydidae). Annals of Carnegie Museum, 62/1: 1-46.

Vogt, R., J. Bull. 1982. Temperature controlled sex-determination in turtles: Ecological and behavioral aspects. Herpetlogica, 38/1: 156-164.

Ziermann, J., M. Sanchez-Villagra, L. Olsson. 2008. Limb chondrogenesis in Graptemys nigrinoda (Emydidae), with comments on the primary axis and the digital arch in turtles. Amphibia-Reptilia, 29/1: 85-92.

van Dijk, P. 2016. "Graptemys nigrinoda (errata version published in 2016)" (On-line). The IUCN Red List of Threatened Species 2011: e.T9502A97420750. Accessed September 04, 2019 at http://dx.doi.org/10.2305/IUCN.UK.2013.RLTS.T9502A12997533.en.

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