Spiny softshell turtle
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The spiny softshell turtle (''Apalone spinifera'') is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
softshell turtle Trionychidae is a family of turtles, commonly known as softshell turtles or simply softshells. The family was described by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to li ...
, one of the largest freshwater turtle species in
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. 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).


Description

The spiny softshell turtle's scientific name is very descriptive of the animal. ''Apalone'' comes from the Greek word ''apalos'', meaning soft or tender, and ''spinifera'' is of Latin origin; ''spina-'' referring to thorn or spine and ''-ifer'' meaning bearing. This species is a member of the family Trionychidae, and one of the most distinguishing features of members in this family is the presence of a leathery, moderately flexible carapace. This is caused by loss of keratinized scutes and some bony tissue loss. Spiny softshell turtles have webbed feet, each with three claws. Another distinguishing feature of softshell turtles is the presence of a fleshy, elongated nose. The carapace (the upper part of the shell) ranges from brown or yellow-brown to olive in color, while the plastron (lower part of the shell) is lighter, usually white or yellow. Hatchlings usually have dark spots on the carapace, but as females age, they frequently become darker in color, or their carapace becomes splotched. Males tend to maintain the same coloration pattern from birth. Coloration also varies between each subspecies, and the exact coloration can also depend on an individual turtle's environment. Spiny softshell turtles are cryptically colored, meaning that their coloration helps them blend in with their surrounding environment. Spiny softshell turtles also have pale lines bordered by black lines running from its head down the side of its neck. The carapace length ranges from , with females growing larger than males. The namesake spines, also known as tubercles, are found along the anterior border of the carapace and are more commonly found in males. The variation in coloration, size, and spine presence indicates that this species exhibits
sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
. ''A. spinifera'' has ridges on its nasal septum, making its nostrils c-shaped, unlike the nostrils of the similar species '' A. mutica'' which are round.


Distribution


Geographic range

This species is the most widely distributed softshell turtle in North America. This could be due to habitat fragmentation caused by humans. The spiny softshell has a wide range, extending throughout much of the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, as well as north into the
Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...
provinces of
Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
and
Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...
, and south into the Mexican states of
Tamaulipas Tamaulipas, officially the Free and Sovereign State of Tamaulipas, is a state in Mexico; one of the 31 states which, along with Mexico City, comprise the 32 federal entities of Mexico. It is divided into 43 municipalities. It is located in nor ...
, Nuevo León, Coahuila and Chihuahua. As of recently, the spiny softshell has expanded its geographic range ( through human assistance) into New Jersey, Massachusetts, New Hampshire, Washington state and
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
. They were also recently discovered in Lake Champlain despite the historical records.


Ecological range

Spiny softshell turtles are often referred to as ecological generalists, meaning that they are found in a wide variety of habitats. The spiny softshell can be found in bodies of fresh water including ponds, lakes, rivers, tributaries, bayous, oxbows and streams. They can persist in more urban environments as they are well adapted to periodic habitat disturbances. They inhabit shallow water less than deep, but can also be found as far as deep. When swimming, a study suggests that they get most of their thrusting power from their forelimbs as opposed to their hindlimbs, which is common in other species. They can be found in areas with varying levels of vegetation, and although they are generally found in more slow-moving waters, this species abundance is greatest in waters with higher visibility and slower water velocity Spiny softshells prefer waters with sandy bottoms and clean, sandy banks. Sandy environments are important for nesting sites, proper juvenile growth and development, and camouflage. Spiny softshells migrate between warm and cold seasons. In each season, turtles generally stay in a single zone, and they move more within their zone during warm months. The spiny softshell will migrate between their zones and their average home range length is . As far as home range, a study of the "eastern spiny" subspecies (which has the largest and most northern-reaching distribution) home range behavior found that turtles of northern
Lake Champlain Lake Champlain ( ; , ) is a natural freshwater lake in North America. It mostly lies between the U.S. states of New York (state), New York and Vermont, but also extends north into the Canadian province of Quebec. The cities of Burlington, Ve ...
generally had two annual concentration areas for spring-summer and fall-winter, contributing to a large home range. Mean annual home range was also found, in the same study, to be over ten times larger for female softshells compared to males. It was suggested in this study that the high home range was due to habitat fragmentation.


Behavior


Diet

Spiny softshell turtles feed on a variety of food items. They are primary consumers and feed on invertebrates (crayfish and aquatic insects), fish, algal stocks and other plant material, and
mussels Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, whic ...
. They are generally observed as benthic feeders; they can either actively hunt prey or bury themselves in the sand and wait to ambush prey. Some evidence suggests that spiny softshell turtles exhibit a nuclear-follower foraging association with fish. A study that took place in an urban drainage canal in
Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...
found that when foraging, spiny softshell turtles were observed moving along the creek bottom thrusting their probosces into the substrate which then allowed fish to enter the suspended sediment and capture prey otherwise unavailable to the fish. The fish benefit from increased foraging success, while few benefits accrue to the foraging turtles.


Reproduction

Spiny softshells begin mating between ages 8 and 10. A large female turtle may live up to 50 years. The turtles mate in mid-to-late spring in deep water. The male will nudge the female's head while swimming and wave their feet in front of her face, and if she chooses to mate, the male will swim above the female without clasping her with his claws (unlike other turtles). Prior to nesting, the females have been observed to have a 3 stage activity pattern throughout the day. The females start the day by basking and moving around an area, then they spend a majority of their afternoon swimming in a new area, and finally they would stop and search for an ideal nesting spot. A few months later, the female turtle quickly lays her eggs along a sunny sandbar or gravel bank in a flask-shaped cavity she has dug close to the water. This nesting behavior typically begins around July with the females leaving the water and probing the ground with her snout to find the spot to lay her eggs. The turtle nests more than once during a single season. She can lay between 9 and 38 round, calcareous-shelled eggs. The eggs are laid around July and September, and they hatch in the spring. Larger bodied females have been found to lay a second clutch in late June or July. In studies observing nesting behavior, it has been found that the females are more likely to lay eggs on days where there is a small difference between the air and water temperatures. Unlike in some other turtles, in the spiny softshell turtle, the sex of the hatchlings is not determined by temperature variations; it is determined by
genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...
. Late-term embryos and hatchlings of spiny softshell turtles have been recently found to make various click- and chirp-type sounds before emergence onto the surface. The function of these sounds is currently unknown.


Respiration

Spiny softshell turtles are bimodal breathers, meaning they have the ability (to some degree) to perform oxygen and carbon dioxide exchange by breathing air or while breathing underwater. A variety of factors allow for these turtles to perform respiration underwater. They have an increase of cutaneous surface area and blood flow, reduction in lung size, and increase of respiratory
epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
in the
cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...
and buccopharynx. This turtle is also known to utilize cutaneous respiration as well.Plummer, Michael V., and Caleb S. O’Neal. “Aerobic Pushups: Cutaneous Ventilation in Overwintering Smooth Softshell Turtles, Apalone Mutica.” Journal of Herpetology, vol. 53, no. 1, 2019, pp. 27–31, www.jstor.org/stable/26908244. Spiny softshell turtles are more dependent on underwater respiration than other freshwater species. This has led to their low tolerance of hypoxic waters; this becomes especially important during times of hibernation, when these turtles must choose hibernacula that are unlikely to become hypoxic. Underwater dormancy can last up to six months. They are known as an anoxia-intolerant species because of their dependency on underwater respiration. Other turtle species are more adapted to variation in oxygen levels but spiny softshell turtles are not able to regulate it as well, especially during hibernation periods. This makes choosing hibernacula very important to their over-winter survival. While they are susceptible to anoxia, they have the ability to maintain their metabolism completely via aerobic means which gives them a slight advantage when compared to other hibernating aquatic turtles during winter.


Conservation

Overall, the spiny softshell turtle is widespread, common and not threatened, but some local populations are under pressure. In Canada, which is at the northern margin of its range and where the species is quite local, it is considered endangered. The very rare black spiny softshell turtle, a subspecies found only in Mexico's Cuatro Ciénegas Basin, is considered
critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...
.


Taxonomy

The
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
was first described by
Charles Alexandre Lesueur Charles Alexandre Lesueur (; 1 January 1778 in Le Havre – 12 December 1846 in Le Havre) was a French Natural history, naturalist, artist, and explorer. He was a prolific natural-history collector, gathering many type specimens in Australia ...
in 1827. It has been redescribed numerous times, leading to some confusion in its
taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
.


Subspecies

The recognized
subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
differ in the markings on their carapaces, on the sides of their heads, and on their feet, although there are also considerable individual (not related to subspecies) variations in the appearance. Their markings, which are distinct as hatchlings, fade as the turtles grow larger. Adult females of the various subspecies, which grow larger than males, are not easily distinguishable from one another, and sometimes can only be assigned to a particular subspecies based on geography. xiv + 494 pp., 47 plates, 207 figures. (''Apalone spinifera'', pp. 232–233 + Plates 20, 22 + Figures 85, 105, 106). Six subspecies of ''A. spinifera'' are recognized, including the
nominate subspecies In biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. ...
: * Northern spiny softshell turtle or eastern spiny softshell,. ''A. s. spinifera'' ( Lesueur, 1827) * Gulf Coast spiny softshell turtle, ''A. s. aspera'' ( Agassiz, 1857) * Black spiny softshell turtle or Cuatro Cienegas softshell turtle, ''A. s. atra'' ( Webb & Legler, 1960) * Texas spiny softshell turtle, ''A. s. emoryi'' ( Agassiz, 1857) * Guadalupe spiny softshell turtle, ''A. s. guadalupensis'' ( Webb, 1962) * Pallid spiny softshell turtle, ''A. s. pallida'' ( Webb, 1962) A previously recognized subspecies, '' Apalone spinifera hartwegi'' ( Conant & Goin, 1941), has been synonymized to ''A. s. spinifera'' as of 2011.


Genomics

A rough-draft assembly of the ''A. spinifera aspera'' genome was completed in 2013 by the Genome Institute at Washington University in St. Louis. The assembly ASM38561v1 can be accessed via its Genbank accession ID APJP00000000.


References

;Bibliography * *


Further reading

* John L. Behler, Behler JL, King FW (1979). ''The Audubon Society Field Guide to North American Reptiles and Amphibians''. New York: Alfred A. Knopf. 743 pp. . (''Trionyx spiniferus'', pp. 485–486 + Plates 270, 271). * Boulenger GA (1889). ''Catalogue of the Chelonians, Rhynchocephalians, and Crocodiles in the British Museum (Natural History). New Edition.'' London: Trustees of the British Museum (Natural History). (Taylor and Francis, printers). x + 311 pp. + Plates I-III. (''Trionyx spinifer'', pp. 259–260). * Lesueur CA (1827). "''Note sur deux espèces de tortues, du genre Trionyx de M nsieur Geoffroy-Saint-Hilaire'' ". ''Mémoires du Muséum d'Histoire Naturelle, Paris'' 15: 257-268 + Plates 6–7. (''Trionyx spiniferus'', new species, pp. 258–263 + Plate 6). (in French). * Smith HM, Brodie ED Jr (1982). ''Reptiles of North America: A Guide to Field Identification''. New York: Golden Press. 240 pp. . (''Trionyx spiniferus'', pp. 31–33). * Stejneger L, Barbour T (1917). ''A Check List of North American Amphibians and Reptiles''. Cambridge Massachusetts: Harvard University Press. 125 pp. (''Amyda spinifera'', p. 125). *


External links


Drawing of skull of Spiny Softshell Turtle
{{Authority control Apalone Turtles of North America Reptiles of the United States Reptiles of Mexico Fauna of the Eastern United States Reptiles of Ontario Reptiles described in 1827 Taxa named by Charles Alexandre Lesueur Fauna of the Northwestern United States