Black-knobbed map turtle

Black-knobbed map turtle
Black-knobbed map turtle hatchlings
Conservation status
Near Threatened  (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Reptilia
Order:	Testudines
Family:	Emydidae
Subfamily:	Deirochelyinae
Genus:	Graptemys
Species:	G. nigrinoda
Binomial name
Graptemys nigrinoda Cagle, 1954
Subspecies
G. n. nigrinoda Cagle, 1954 (black-knobbed map turtle) G. n. delticola Folkerts & Mount, 1969 (delta map turtle)[1]
Range map
Synonyms[2]
Graptemys nigrinoda nigrinoda Graptemys nigrinoda Cagle, 1954 Graptemys oculifera nigrinoda — Mertens & Wermuth, 1955 Graptemys nigrinoda nigrinoda — Folkerts & Mount, 1969 Malaclemys nigrinoda — Cochran & Goin, 1970 Graptemys nigrinoda delticola Graptemys nigrinoda delticola Folkerts & Mount, 1969

The black-knobbed map turtle (Graptemys nigrinoda), formerly known as the black-knobbed sawback, is a small to medium-sized aquatic turtle with light gray skin.^[3] Some of the most distinguishing characteristics of the black-knobbed map turtle, and the Graptemys genus, are the protruding “spikes” on the turtle’s carapace. This species inhabits mainly the fall lines of rivers in the Mobile Bay drainage, in Alabama and Mississippi.^[4]

Description

The carapace of G. nigrinoda is slightly domed with the first four vertebrae possessing backward-projecting, knob-like processes, which are black in color. The second and third processes are more dominant in size compared to the first and fourth. With aging females, the knobs are reduced to small swellings.^[3]

The carapace is dark olive-brown in color.^[4] Within each pleural, or "plate", of the shell are yellow-green circular rings which are outlined in black.^[3] Hatchlings are similar in color to adults, but the colors tend to be more vibrant and contrasting.^[5] The knob-like processes are compressed laterally.

The head is small, and is dark brown with yellow stripes, with yellow crescents behind the eye facing towards the posterior end of the turtle. These stripes continue on the legs of the turtle also, with the underside of the leg being lighter than the dorsal surface.^[6]

Sexual dimorphism is evident in this species. Females are roughly twice the size of males. Also, females’ carapaces tend to be higher than those of males, though the males have longer tails than the females.^[5] Sizes (carapace lengths) have been recorded as ranging from 7.6-10.2 cm (3-4 in) in males and 10.2-19.1 cm (4-7.5 in) in females.

Distribution

The black-knobbed map turtle is endemic to the southeastern United States.^[3] In Alabama, they are found in the Mobile Bay drainage. In Mississippi, they are found in the Tombigbee River system and in the Black Warrior River as far north as Jefferson County, Alabama.^[3] They are only able to survive in fresh water, thus they are only found within freshwater river systems.^[3]

Habitat and ecology

Black-knobbed map turtles are seasonally active from April to late November.^[5] Basking is a routine part of their day, occurring in the early morning and early afternoon.^[5][7] Thermoregulation is thought to be the reason for basking, along with the removal of parasites and algal growth.^[7]

When approached, the turtles jump into the nearby water. Once in the water, they seek protection between the branches of fallen trees on the river bottom.^[8] Most of the riverbeds where they live have sand and clay bottoms with moderate currents.^[4] Hatchlings prefer more sluggish waters off the main channel.^[3]

Little is known about foraging behavior. However, this species has been observed to consume beetles and dragonflies that have fallen into the river.^[7] Upon examination of both female and male stomach matter, Lahanas^[5] found a distinction of food material percentages. Males had roughly 58% animal matter and 40% plant matter, while females had 70% animal matter and 29% plant matter. The three primary sources of animal matter came from freshwater sponges, bryozoans, and mollusks. The only plant matter found was a freshwater alga.

Males reach sexual maturity around 3–4 years and females reach it around 7–8 years. Females have a clutch size of roughly five eggs and can lay three or four clutches in a year.^[3] Nesting occurs from May to August, and occurs nocturnally on a sandbank.^[5] This species feeds primarily on insects.^[4]

Conservation

Currently, this species has been petitioned and is under consideration for listing by the U.S. Fish and Wildlife Service in subcategory 3-C, but classified as Near Threatened by the IUCN Red List. The black-knobbed map turtle is most likely threatened by habitat degradation and encroachment by humans. Humans have been known to remove dead logs that line the shoreline of rivers, which the turtle uses for basking in the sun. Also, indirect disturbances of nest sites may become an issue. Additionally, the turtle population could decline due to the consumption of their eggs by humans or other predators.^[5] Fisherman, though, in most cases not purposely, can kill turtles with their trotlines, gill nets, and hoop nets.^[5]

Most of the lands encompassed by the species habitat are protected lands, but the rivers remain vulnerable. Mobile River Basin Aquatic Ecosystem Recovery Plan^[9] has been implemented to address the needs of 22 aquatic species. One of these species is the red-bellied turtle (Pseudemys rubriventris), whose habitat overlaps with G. nigrinoda, so the plan will be beneficial to the black-knobbed map turtle.

Captive breeding has been an option for conservation efforts, also. Captive breeding is plausible for increasing population sizes in captivity.^[7] However, it remains unclear if captive-bred black-knobbed map turtles can be released into the wild and breed on their own. Black-knobbed map turtles are popular in the pet trade, but became more common because of captive breeding.

References

Wikimedia Commons has media related to Graptemys nigrinoda.

Further reading

• Cagle, F.R. 1954. Two New Species of the Genus Graptemys. Tulane Studies in Zoology 1 (11): 165-186.

• Conant, R. 1975. A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Second Edition. Houghton Mifflin. Boston. xviii + 429 pp. + 48 plates. ISBN 0-395-19979-4 (hardcover), ISBN 0-395-19977-8 (paperback). (Graptemys nigrinoda, p. 59 + Plate 8 + Map 17.)

• Smith, H.M., and E.D. Brodie, Jr. Reptiles of North America: A Guide to Field Identification. Golden Press. New York. 240 pp. ISBN 0-307-13666-3 (paperback). (Graptemys nigrinoda, pp. 52–53.)

External links

• Tortoise & Freshwater Turtle Specialist Group 1996. Graptemys nigrinoda. 2006 IUCN Red List of Threatened Species. Downloaded on 29 July 2007.

Family Emydidae (pond turtles) Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Testudines Suborder: Cryptodira Superfamily: Testudinoidea Family: Emydidae Genus Species of the subfamily Deirochelyinae Chrysemys Painted turtle Deirochelys Chicken turtle Graptemys Alabama map turtle Barbour's map turtle Black-knobbed map turtle Cagle's map turtle Escambia map turtle False map turtle Northern map turtle Ouachita map turtle Pascagoula map turtle Pearl River map turtle Ringed map turtle Texas map turtle Yellow-blotched map turtle Malaclemys Diamondback terrapin Pseudemys Alabama red-bellied cooter Northern red-bellied cooter Florida red-bellied cooter Peninsula cooter Rio Grande cooter River cooter Texas river cooter Trachemys Big bend slider Baja California slider Central Antillean slider Colombian slider Cuatro Cienegas slider Cuban slider D'Orbigny's slider Hispaniolan slider Jamaican slider Maranhão slider Meso-American slider Nicaraguan slider Ornate slider Pond slider Yaqui slider   Species of the subfamily Emydinae Clemmys Spotted turtle Emys Blanding's turtle European pond turtle Sicilian pond turtle Western pond turtle Glyptemys Bog turtle Wood turtle Terrapene Coahuilan box turtle Common box turtle Ornate box turtle Spotted box turtle Phylogenetic arrangement based on turtles of the world 2011 update: annotated checklist. Subspecies and the extinct (Gyremys sectabilis) are not included.