Twist-necked turtle
Encyclopedia
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. Platemys platycephala or the twist-necked turtle 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 Surinam- a country in northern South America. In other words, diploid and triploid levels exist within and among individuals at this particular location. No threats have been reported for this species and IUCN (International Union for Conservation of Nature) does not have a current listing. Lack of consumption due to the species' small size and inability to reproduce in captivity help explain why scientists are not concerned about this turtle species.
) 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
. Platemys platycephala inhabits a wide range compared to other Acanthochelys turtles, see distribution. Two subspecies, Platemys platycephala platycephala and Platemys platycephala melanonota exist based on color pattern, see subspecies distribution. Camouflage
is highly useful for the twist-necked turtle because it inhabits shallow pools and creek beds. The orange and brown head pattern make it difficult to spot from above because of similarly colored leaf litter among small pools and creek beds. Other distinctions include a hook at the base of the foot for copulation in males and an specialized opening at the base of the plastron for oviposition
(egg deposit).
(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. 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 projection and scales that protect against predator attack.
Platemys platycephala is a member of Pleurodira
- a suborder of turtle. These turtles withdraw their head into their shell by bending their necks sideways instead of straight back like Cryptodira
. The snout projects slightly and the irises are brown. Black limbs consist of 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.
levels (number of sets of chromosomes) for somatic
and gametic
cells on a few specimens in Suriname. 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. Additionally, Platemys 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 cytogenic 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. Several hypotheses were tested using phylogenetic data from mitochondrial DNA (mtDNA), but a high level of divergence was found for the three monophyletic populations.
, from the southern Orinoco
drainage in Venezuela to the Amazon basin
in Brazil
). However, Platemys platycephala, does not inhabit large rivers but instead prefers shallow creeks and forest floors.
Ernst (1983) surveyed the extensive geographical range of the twist-necked turtle and determined the presence of a dark subspecies in the western range of Platemys platycephala. 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- Platemys platycephala melanonota.
, Guianas, Venezuela
, Suriname
) while P. p. melanonata inhabits the western territory (Peru
, Ecuador
). 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. These subspecies interbreed in Bolivia
and various river drainages (Río Madre de Dios, Río Mamoré and Ucayali) frequently forming variations in shell pattern.
(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’ head. Some authors also report violent biting and water expulsion from the males nostrils during copulation. Coupling has been observed on land or in water and usually occurs late in the afternoon or at night. Oviposition
comes 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 couple of weeks later while some recreational collectors report multiple eggs at a time. Shallow indentations are made to deposit eggs and then lightly covered by sand and/or leaf litter.
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 is expected to occur.
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. 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. Platemys platycephala or the twist-necked turtle 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
Amazon Rainforest
The Amazon Rainforest , also known in English as Amazonia or the Amazon Jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America...
for insects, amphibians, and mollusks. Camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
, head and body shape, and advanced sexual anatomy allow this species of turtle to effectively populate much of South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. 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 Surinam- a country in northern South America. In other words, diploid and triploid levels exist within and among individuals at this particular location. No threats have been reported for this species and IUCN (International Union for Conservation of Nature) does not have a current listing. Lack of consumption due to the species' small size and inability to reproduce in captivity help explain why scientists are not concerned about this turtle species.
Diagnosis
The twist-necked turtle now represents the only species of Platemys and can be distinguished from close relatives (AcanthochelysAcanthochelys
Acanthochelys is a genus of turtle in the Chelidae family.It contains the following species:* Big-headed pantanal swamp turtle * Chaco side-necked turtle...
) 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
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
. Platemys platycephala inhabits a wide range compared to other Acanthochelys turtles, see distribution. Two subspecies, Platemys platycephala platycephala and Platemys platycephala melanonota exist based on color pattern, see subspecies distribution. Camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
is highly useful for the twist-necked turtle because it inhabits shallow pools and creek beds. The orange and brown head pattern make it difficult to spot from above because of similarly colored leaf litter among small pools and creek beds. Other distinctions include a hook at the base of the foot for copulation in males and an specialized opening at the base of the plastron for oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
(egg deposit).
Description
Platemys platycephala is a medium-sized turtle ranging from 14–18 cm in shell length. Females are slightly smaller on average with shorter tails. The carapaceCarapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...
(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. 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 projection and scales that protect against predator attack.
Platemys platycephala is a member of Pleurodira
Pleurodira
The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. In many cases in the nomenclature of animals, ranks such as suborder are considered of little importance apart from nomenclatural or taxonomic reasons. However, this is not the case with the suborders of...
- a suborder of turtle. These turtles withdraw their head into their shell by bending their necks sideways instead of straight back like Cryptodira
Cryptodira
Cryptodira is the taxonomic suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira in that they lower their necks and pull the heads straight back into the shells; instead of folding their necks sideways along the body under the shells' margins...
. The snout projects slightly and the irises are brown. Black limbs consist of 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.
Genetics
A few interesting genetics studies exist for the twist-necked turtle (Platemys platycephala). Bickham et al. (1993) performed a small-scale cytological survey on the ploidyPloidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
levels (number of sets of chromosomes) for somatic
Somatic
The term somatic means 'of the body',, relating to the body. In medicine, somatic illness is bodily, not mental, illness. The term is often used in biology to refer to the cells of the body in contrast to the germ line cells which usually give rise to the gametes...
and gametic
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
cells on a few specimens in Suriname. 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
Lacertidae
Lacertidae is the family of the wall lizards, true lizards, or sometimes simply lacertas, which are native to Europe, Africa, and Asia. The group includes the genus Lacerta, which contains some of the most commonly seen lizard species in Europe...
and fish genus Phoxinus
Phoxinus
Phoxinus is a genus of freshwater fish in the carp family of order Cypriniformes. The type species is Phoxinus phoxinus, the Common Minnow. The North American members of this genus are known as daces, and the Old World ones as Eurasian minnows. The latter term is also used specifically for P...
are the only other known examples of diploid-triploid mosaicism. Additionally, Platemys 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 cytogenic 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. 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 AmericaSouth America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, from the southern Orinoco
Orinoco
The Orinoco is one of the longest rivers in South America at . Its drainage basin, sometimes called the Orinoquia, covers , with 76.3% of it in Venezuela and the remainder in Colombia...
drainage in Venezuela to the Amazon basin
Amazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
). However, Platemys platycephala, does not inhabit large rivers but instead prefers shallow creeks and forest floors.
Ernst (1983) surveyed the extensive geographical range of the twist-necked turtle and determined the presence of a dark subspecies in the western range of Platemys platycephala. 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
Allopatric speciation
Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
to occur among many species and gave rise to a new subspecies- Platemys platycephala melanonota.
Subspecies
Two subspecies exist for the twist-necked turtle- Platemys platycephala platycephala and Platemys platycephala melanonota. P. p. platycephala inhabits most of the central and eastern territory (BrazilBrazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, Guianas, Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
, Suriname
Suriname
Suriname , officially the Republic of Suriname , is a country in northern South America. It borders French Guiana to the east, Guyana to the west, Brazil to the south, and on the north by the Atlantic Ocean. Suriname was a former colony of the British and of the Dutch, and was previously known as...
) while P. p. melanonata inhabits the western territory (Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
, Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
). 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. These subspecies interbreed in Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
and various river drainages (Río Madre de Dios, Río Mamoré and Ucayali) frequently forming variations in shell pattern.
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, veggies, insects, worms and even fish. Platemys platycephala are likely to be found in shallow pools and can inhabit dry areas for long periods of time. Fretey (1975) states several individuals can even become heavily parasitized by leeches (81 suckers found on one turtle) during the dormant dry season and suffer accordingly.Life History
Platemys platycephala 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 rainforestAmazon Rainforest
The Amazon Rainforest , also known in English as Amazonia or the Amazon Jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America...
(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’ head. Some authors also report violent biting and water expulsion from the males nostrils during copulation. Coupling has been observed on land or in water and usually occurs late in the afternoon or at night. Oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
comes 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 couple of weeks later while some recreational collectors report multiple eggs at a time. Shallow indentations are made to deposit eggs and then lightly covered by sand and/or leaf litter.
Conservation
No direct threats are evident for Platemys platycephala because human consumption is inefficient due to the small size of the turtle. Additionally, this turtle does not perform well in captivity so the pet market is minimal but some amateurs do try,. 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 ListIUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
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 is expected to occur.