Twist-necked turtle

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Twist-necked turtle
Twist-neck Turtle (Platemys platycephala) (10358928446).jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Pleurodira
Family: Chelidae
Subfamily: Chelinae
Genus: Platemys
Wagler, 1830
Species:
P. platycephala
Binomial name
Platemys platycephala
Schneider, 1792 [2]
Synonyms [1]
P. p. platycephala (Schneider 1792)
  • Testudo platycephala Schneider 1792:261
  • Testudo planiceps Schneider 1792:pl.7 (senior homonym)
  • Testudo martinella Daudin 1802:377
  • Emys discolor Thunberg in Schweigger 1812:302
  • Emys canaliculata Spix 1824:10
  • Emys carunculata Saint-Hilaire in Cuvier 1829:11 ( nomen nudum et dubium )
  • Emys constricta Cuvier in Gray 1830e:17 ( nomen nudum )
  • Hydraspis pachyura Boie in Gray 1830e:17 ( nomen nudum )
  • Hydraspis constricta Gray 1831d:43
P. p. melanonota Ernst 1984
  • Platemys platycephala melanonota Ernst 1984:347

The twist-necked turtle (Platemys platycephala), also known as the flat-headed turtle, is distributed widely across northern South America. Twist-necked turtles have extremely flat shells that help them hide from predators under rocks and debris. When threatened, this turtle withdraws by twisting its head into its shell. P. platycephala is the only species of the genus Platemys and occurs in northern and central South America. Platemys platycephala means "flat turtle, flat-head" and accurately describes the structure of the head and shell. This species inhabits shallow creek beds and frequently forages on the floor of the Amazon rainforest for insects, amphibians, and mollusks. Camouflage, head and body shape, and advanced sexual anatomy allow this species of turtle to effectively populate much of South America. Mating occurs during rainy months (March–December) and egg deposit occurs during dry months (January–March). Males have been known to behave aggressively towards females during copulation by squirting water from nostrils and biting. A few genomic studies show mosaicism exists among populations of the twist-necked turtle in Suriname. In other words, diploid and triploid levels exist among individuals at this particular location. No threats have been reported for this species and the International Union for Conservation of Nature does not have a current listing. Lack of human consumption due to the species' small size and its wide range explain why scientists are not concerned about this turtle species.

Contents

Diagnosis

The twist-necked turtle now represents the only species of Platemys and can be distinguished from close relatives ( Acanthochelys ) by its doubly flat body plan, both a flattened shell and a flattened head. Also, this turtle displays an unusual dual grooved pattern on the carapace. P. platycephala inhabits a wide range compared to other Acanthochelys turtles. Two subspecies, P. p. platycephala and P. p. melanonota is described based on the color pattern. Camouflage is highly useful for the twist-necked turtle because it inhabits shallow pools and creek beds. The orange and brown head pattern makes it difficult to spot from above because of similarly colored leaf litter along small pools and creek beds. Other distinctions include a hook at the base of the foot for copulation in males and a specialized opening at the base of the plastron for oviposition (egg deposit).

Description

P. platycephala is a medium-sized turtle ranging from 14 to 18 cm in shell length. [3] Females are slightly smaller on average, with shorter tails. The carapace (top portion of the shell) is elliptical and flattened with two raised portions (keels) forming a trough (depression). The carapace is orange to yellow-brown and black in various amounts depending on subspecies. [3] The plastron (lower portion of the shell) is dark brown or black in color while the bridge (side portion of the shell) is yellow with a black bar across. The consistency of these bars also depends on subspecies. Face and neck patterns consist of orange or yellow-brown dorsal stripes and black ventral and lateral stripes. The head is small, triangular, smooth, and undivided. The neck has some conical tubercles- rounded projections and scales that protect against predator attack. P. platycephala is a member of the Pleurodira- a suborder of turtles. These turtles withdraw their heads into their shells by bending their necks sideways instead of straight back like Cryptodira. The snout projects slightly and the irises are brown. Black limbs contain large anterior scales, while the tail is short and black. Intermediate webbing exists on both anterior and posterior limbs because this turtle moves in water and on land. [4]

Genetics

A few interesting genetics studies exist for the twist-necked turtle. Bickham et al. (1993) performed a small-scale cytological survey on the ploidy levels (number of sets of chromosomes) for somatic and gametic cells on a few specimens in Suriname. [5] The authors examined multiple tissues (spleen, liver, blood, testis) of six specimens (five males, one female) and found cells contained various ploidy levels within and among individuals. One male individual even consisted of triploid-tetraploid cells. More genetic variation was found with respect to diploid (2n) to triploid (3n) ratio occurred among individuals than within individuals. Also, diploid cells exclusively participated in meiosis and subsequent sexual reproduction for males, so balanced gametes and normal fertility occurred.

This is a rare event because of the limited viable polyploid individuals that occur in natural vertebrate populations. The lizard genus Lacerta and fish genus Phoxinus are the only other known examples of diploid-triploid mosaicism. [6] [7] Additionally, P. platycephala contains several combinations of ploidy level (x n) in various cell or tissue types. This phenomenon is known as mosaicism or chimerism. In a follow-up study, Bickham & Hanks (2009) performed cytogenetic analysis of the twist-necked turtle to determine how widespread this process is throughout South America, and discovered normal diploid populations exist in Bolivia, while variable mosaic populations persist in Suriname. Additionally, Darr et al. (2006) found turtle populations from French Guiana had increased triploid frequency compared to both Bolivia and Suriname. [8] Several hypotheses were tested using phylogenetic data from mitochondrial DNA (mtDNA), but a high level of divergence was found for the three monophyletic populations.

Distribution

The twist-necked turtle inhabits a large area throughout northern and central South America, from the southern Orinoco drainage in Venezuela to the Amazon basin. However, P. platycephala does not inhabit large rivers, but instead is found in shallow creeks and on forest floors. [9]

Ernst (1983) surveyed the extensive geographical range of the twist-necked turtle and determined the presence of a dark subspecies in its western range. The author uses the "Quaternary forest refuge theory" to explain the existence of this subspecies. The theory is based on significant climatic changes occurring in and around the equator during the Quaternary period. During these climatic changes of glaciation, the northern rainforests of South America received less rainfall and deteriorated, then subsequently expanded during interglaciation. This change caused allopatric speciation to occur among many species and gave rise to a new subspecies - P. p. melanonota. [10]

Subspecies

Two subspecies exist for the twist-necked turtle; P. p. platycephala inhabits most of the central and eastern territory (Brazil, Guianas, Venezuela, Colombia, Bolivia and most of its Peruvian range), while P. p. melanonata inhabits the western territory (Ecuador and adjacent northern Peru). [1] The chief distinction between these subspecies is the carapace coloration. P. p. melanonata, (western twist-necked turtle or black-backed twist-necked turtle), has an entirely dark brown or black top shell.[ citation needed ]

Ecology

The coloration and shape of the carapace, head, and feet help conceal this species of turtle from Amazon predator species. Naturally, twist-necked individuals prefer amphibian eggs and consume various insects, mollusks (snails and slugs), amphibians, and some plant life through terrestrial and aquatic foraging. In captivity, specimens can flourish on reptile food, vegetables, insects, worms, and even fish. P. platycephala is likely to be found in shallow pools and can inhabit dry areas for long periods of time. Several individuals can even become heavily parasitized by leeches (81 suckers found on one turtle) during the dormant dry season and suffer accordingly. [11]

Life history

The young or hatchlings typically resemble parents except for brighter coloration. Twist-necked hatchlings measure around 4–6 cm in carapace length and about 20 g or 0.04 lbs. Mating typically occurs during the rainy season of the Amazon rainforest (late March to early December). Males follow females, mount from behind, then proceed to rub their chin barbels (fleshy filament) against the top of females’ heads. Some authors also report violent biting and water expulsion from the males' nostrils during copulation. [12] Coupling has been observed on land and in water, and usually occurs late in the afternoon or at night. Oviposition occurs during the dry season (late December to early March) when the female deposits a large, oval egg (around 5 cm long and 2.5 cm wide). Many herpetologists report females depositing another egg a few weeks later while some recreational collectors report multiple eggs at a time. Shallow indentations are made to deposit eggs, and then they are lightly covered by sand and/or leaf litter.[ citation needed ]

Conservation

P. platycephala is rarely hunted for human consumption due to its small size. In captivity, this turtle is susceptible to fungal infections and is not considered a beginner's species. [13] Very few have managed to breed it, and most seen in captivity were taken from the wild. [14] France placed this species on its list of protected species for French Guiana and prohibits the capture of any specimens, for hunting, trading, etc. The IUCN Red List does not currently list this species. Additionally, the USGS reports a few twist-necked specimens were found on a southern Florida golf course, but no impact on native species is expected to occur. [15]

Related Research Articles

<span class="mw-page-title-main">Ploidy</span> Number of sets of chromosomes in a cell

Ploidy is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively, in each homologous chromosome pair, which chromosomes naturally exist as. Somatic cells, tissues, and individual organisms can be described according to the number of sets of chromosomes present : monoploid, diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid or septaploid, etc. The generic term polyploid is often used to describe cells with three or more chromosome sets.

<span class="mw-page-title-main">Red-eared slider</span> Subspecies of turtle

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<span class="mw-page-title-main">Chelidae</span> Family of turtles

Chelidae is one of three living families of the turtle suborder Pleurodira, and are commonly called Austro-South American side-neck turtles. The family is distributed in Australia, New Guinea, parts of Indonesia, and throughout most of South America. It is a large family of turtles with a significant fossil history dating back to the Cretaceous. The family is entirely Gondwanan in origin, with no members found outside Gondwana, either in the present day or as a fossil.

<span class="mw-page-title-main">Spotted turtle</span> Species of turtle

The spotted turtle, the only species of the genus Clemmys, is a small, semi-aquatic turtle that reaches a carapace length of 8–12 cm (3.1–4.7 in) upon adulthood. Their broad, smooth, low dark-colored upper shell, or carapace, ranges in its exact colour from black to a bluish black with a number of tiny yellow round spots. The spotting patterning extends from the head, to the neck and out onto the limbs. Sexually mature males have a concave plastron and a long, thick tail. By contrast, sexually mature females possess a flat plastron and have a tail notable shorter and thinner than mature males. Mature males also have a dark iris and face; females typically have a yellow or orange iris and a similarly coloured face that is distinctly lighter than males. Juveniles appear female-like in this regard and at maturity males begin to develop darker features.

<span class="mw-page-title-main">Chicken turtle</span> Species of turtle

The chicken turtle is a turtle native to the southeastern United States. It is the only extant member of the genus Deirochelys and is a member of the freshwater marsh turtle family Emydidae. The chicken turtle's scientific name refers to its extremely long neck and distinctive net-like pattern on its upper shell. There are three regionally distinct subspecies, which are thought to have evolved when populations became separated during periods of glaciation. These subspecies can be distinguished by their appearance; the western chicken turtle displays dark markings along the seams of its plastron, while the plastron of the Florida subspecies is a bright yellow or orange color. Fossil records show that the chicken turtle has been present in the region for up to five million years.

<span class="mw-page-title-main">African helmeted turtle</span> Species of turtle

The African helmeted turtle, also known commonly as the marsh terrapin, the crocodile turtle, or in the pet trade as the African side-necked turtle, is a species of omnivorous side-necked terrapin in the family Pelomedusidae. The species naturally occurs in fresh and stagnant water bodies throughout much of Sub-Saharan Africa, and in southern Yemen.

<span class="mw-page-title-main">Red-footed tortoise</span> Species of tortoise

The red-footed tortoise is a species of tortoise from northern South America. These medium-sized tortoises generally average 30 cm (12 in) as adults, but can reach over 40 cm (16 in). They have dark-colored, loaf-shaped carapaces with a lighter patch in the middle of each scute, and dark limbs with brightly colored scales that range from pale yellow to dark red. Recognized differences are seen between red-footed tortoises from different regions. They are closely related to the yellow-footed tortoise from the Amazon Basin. They are popularly kept as pets, and over-collection has caused them to be vulnerable to extinction.The species name has often been misspelled as carbonaria, an error introduced in the 1980s when Chelonoidis was elevated to genus and mistakenly treated as feminine, an error recognized and fixed in 2017.

<span class="mw-page-title-main">Indian black turtle</span> Species of reptile found in South Asia

The Indian black turtle or Indian pond terrapin is a species of medium-sized freshwater turtle found in South Asia.

<span class="mw-page-title-main">Amboina box turtle</span> Species of turtle

The Amboina box turtle or Southeast Asian box turtle is a species of Asian box turtle.

<span class="mw-page-title-main">Indian roofed turtle</span> Species of turtle

The Indian roofed turtle is a species of turtle in the family Geoemydidae. It can be distinguished by the distinct "roof" at the topmost part of the shell. It is found in the major rivers of South Asia. It is a common pet in the Indian Subcontinent.

<span class="mw-page-title-main">Common box turtle</span> Species of turtle

The common box turtle is a species of box turtle with six existing subspecies. It is found throughout the Eastern United States and Mexico. The box turtle has a distinctive hinged lowered shell that allows it to completely enclose itself. Its upper jaw is long and curved.

<i>Graptemys</i> Genus of turtles

Graptemys is a genus of freshwater turtles containing 14 species, commonly known as map turtles. Graptemys are small to medium-sized turtles that are sexually dimorphic, with females attaining as much as twice the length and ten times the mass as males in some species. Depending on the species, adult males range from 7–16 cm (2.75–6.25 in), adult females 10–29.5 cm (4–11.62 in), and hatchlings 2.5–3.8 cm (1–1.5 in), although some sources indicate female Barbour's map turtles grow to 33 cm (13 in) in length. Most species have a distinctive dark pigmented keel that is often notched or serrated running down the center of the carapace and serrated scutes on the rear margin. The head, neck, and limbs exhibit bold patterns of yellow lines and spots against darker green, olive, or black base colors. The patterns on the head can be important characters in identifying the various species. The common name "map turtle" is derived from the intricate patterns on their shells that are suggestive of topographical maps, although the patterns are more apparent in some species than others, and often become obscure in older specimens. Some species are occasionally called "sawbacks", in reference to the serrated keels on their shell.

<span class="mw-page-title-main">Spiny softshell turtle</span> Species of turtle

The spiny softshell turtle is a species of softshell turtle, one of the largest freshwater turtle species in North America. Both the common name, spiny softshell, and the specific name, spinifera (spine-bearing), refer to the spiny, cone-like projections on the leading edge of the carapace, which are not scutes (scales).

<span class="mw-page-title-main">Wood turtle</span> Species of turtle

The wood turtle is a species of turtle endemic to North America. It is in the genus Glyptemys, a genus which contains only one other species of turtle: the bog turtle. The wood turtle reaches a straight carapace length of 14 to 20 centimeters, its defining characteristic being the pyramidal shape of the scutes on its upper shell. Morphologically, it is similar to the bog turtle, spotted turtle, and Blanding's turtle. The wood turtle exists in a broad geographic range extending from Nova Scotia in the north to Minnesota in the west and Virginia in the south. In the past, it was forced south by encroaching glaciers: skeletal remains have been found as far south as Georgia.

<span class="mw-page-title-main">Caspian turtle</span> Species of turtle

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The big-headed pantanal swamp turtle or pantanal swamp turtle is a species of turtle in the family Chelidae found in Brazil, Bolivia, Argentina, and Paraguay.

<span class="mw-page-title-main">Yellow-footed tortoise</span> Species of reptile

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<span class="mw-page-title-main">Black marsh turtle</span> Species of turtle

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References

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