(Boidae)
Class Reptilia
There are more than 40 species of true boas (family Boidae). In addition, boa may also refer to two other groups of snakes: the Mascarene, or split-jawed, boas (family Bolyeriidae) and dwarf boas (ground and wood boas of the family Tropidophiidae); these two families are not closely related to each other or to the true boas. © 2017 What Snake Is That All images reproduced with permission All images reproduced with permission.
Order Squamata
Suborder Serpentes
Family Boidae
Thumbnail description
Small to giant constricting snakes possessing paired lungs, cloacal spurs, and toothless premaxilla; most species are viviparous
Size
1.2–25 ft (0.37–7.7 m); 0.2–320+ lb (0.1–145+ kg)
Number of genera, species
7 genera; 41 species
Habitat
Loose sand, burrows, grasslands, savanna, forest, various freshwater habitats
Conservation status
Endangered: 1 species; Vulnerable: 4 species; Lower Risk/Near Threatened: 2 species
Distribution
South America, Central America, Mexico, southwestern Canada, western United States, and West Indies; southeastern Europe and Asia Minor; sub-Saharan western Africa east to Tanzania, north through Egypt, and Mediterranean coast from Egypt to eastern Morocco; Madagascar and Reunion Island; Arabian Peninsula; southwestern and central Asia; Indian subcontinent and Sri Lanka; Sulawesi, Moluccan Islands; New Guinea; Bismarck Archipelago; and Melanesia east to American Samoa
Evolution and systematics
Fossil snake skulls are rarely recovered because the bones of the skull are small and loosely connected and typically become separated soon after death. Vertebrae are the most common snake fossil. In general, few snake families can be identified incontrovertibly by vertebrae and ribs. Living erycine snakes, however, have several unique vertebral characters, and on this basis numerous fossil vertebrae have been identified as erycine (in the subfamily Erycinae).
The modern Boidae is believed to have descended from basal macrostomatans; it is one of several snake lineages that diverged from the primitive alethinophidians (true snakes) near the end of the Cretaceous. Macrostomatan snakes are distinguished by characters of the skull and musculature that allow them increased jaw flexibility, a greater gape, and the ability to consume larger prey.
Boid snakes share many characters with other basal macrostomatan snakes, including fully functional paired lungs, smooth scales (with some exceptions) vestiges of a pelvic girdle, and cloacal spurs. The cloacal spurs of boas are two claw-like structures that are located one on each side of the anal scale. They are usually larger in male boas than in females; the females of some species may not have apparent cloacal spurs. Characters shared with the Pythonidae, the sister taxon of the Boidae, include elliptical pupils and pitted lip scales. The pits in the lips are associated with thermoreception, the ability to detect differences in temperature.
Boas differ from pythons in numerous characters, including: Boid snakes do not have a supraorbital bone (with one exception) while all pythons have a supraorbital bone. Not all boas have labial pits; when present, the labial pits are located between the labial scales while the labial pits of pythons are centered in the labial scales. Two premaxilla are fused together to form a small bone across the front of the upper jaw; the premaxilla of boid snakes is without teeth while the premaxilla of most pythons is toothed. Most boas are viviparous, meaning they bear live young; all pythons lay eggs. Three taxa of boid snakes, Charina reinhardtii, Eryx muelleri, and Eryx jayakari, are oviparous and lay eggs.
Undoubtedly, the Boidae is more speciose than is recognized. An analysis of the geographic variation and systematic relationships of populations of Boa constrictor, the most widely distributed boid species, has yet to be accomplished. Likewise, the systematic relationships of the insular populations of all three species of Candoia remain to be investigated fully. There is little doubt that there will be further taxonomic changes within the Boidae.
As of 2002, science recognizes 41 species in seven genera and two subfamilies in the Boidae. The Boinae, the larger subfamily, includes the boas and anacondas, 27 species in five genera. The Erycinae includes the sandboa, rubber boa, rosy boa, and Calabar boa, 14 species in two genera. The division of the Boidae into these two subfamilies is based primarily on osteological characters.
Physical characteristics
The Boidae is distributed widely on five continents and countless islands and occurs in many different habitats.
Among the species, great variation in size, scalation, diet, habitat, and many other characters can be seen. There are several species of erycine snakes that are not known to exceed 3 ft (1 m) in length. The Haitian vine boa, Epicrates gracilis, is one of the most elongate and slender of all snakes. The boa constrictor is a large species, approaching 15 ft (4.6 m) in maximum length.
The green anaconda, Eunectes murinus, is the largest boid snake. Its maximum size is a topic of controversy. There are stories and reports in the literature of anacondas measuring 33–45 ft (10–14 m). Murphy and Henderson list 25 ft (7.7 m) as the longest specimen whose length actually was measured, not just estimated. This anaconda is probably the heaviest snake species in the world. While all of the giant snake species attain great weight in captivity, there are numerous records of wild specimens of green anacondas exceeding 300 lb (136 kg).
With the exception of the rosy boa, Charina trivirgata, the bodies of erycine snakes are modified for burrowing. The eyes are small and often set high on the sides of their heads, the rostrals (scales on the end of the snout) are strong and broad, and the lower jaws are underslung and close tightly. The heads are narrow and the necks thick, the bodies are round and usually smooth scaled, and the tails are short with thickened skin on the upper surfaces. Several species have blunt tails. No erycine snakes have labial pits or have been shown to have well-developed temperature-sensing abilities. The largest erycine snake is the brown sandboa, Eryx johnii; this species reaches a maximum length slightly exceeding 4 ft (1.3 m). There are several small species—the smallest is probably the Arabian sandboa, E. jayakari, with an average adult size of 0.9 ft (28 cm).
The boine snakes are mostly medium sized, athletic, terrestrial, and arboreal. The smallest species is the Abaco boa, Epicrates exsul, with a maximum length of 31.5 in (810 mm). The best-known arboreal species is the emerald tree boa, Corallus caninus. The anacondas are the largest and most aquatic of the boas; they have soft, loose skin that can withstand long periods of immersion, and their eyes and nostrils are directed upward, so that they can see and breathe with most of the head submerged. Most boine snakes have large heads that are distinctly wider than their necks, large eyes, laterally compressed bodies (to varying degrees), and long tails. Most have temperature-sensing labial pits, and several species in the genera Boa and Eunectes have temperature-sensing abilities even without labial pits.
The boas include many beautiful species. Several species have a polymorphic appearance; one such species is the Amazon tree boa, Corallus hortulanus, with patterned and unpatterned appearances that vary in color from gray to brown to yellow to orange to red. The skin of many species exhibits a beautiful iridescence. Some populations of the boa constrictor, B. constrictor, and the rainbow boa, Epicrates cenchria, have a remarkable ability to change the color of their skin; they typically appear darkest during the day and much paler at night. The Fiji Island boa, Candoia bibroni, has been seen to change from black to pale pink in a period of six hours.
Distribution
The Boidae has one of the most extensive distributions of a snake family. Several genera have disjunct distributions. In the Boinae, Boa occurs in northwestern and northeastern Mexico south through Central and South America, the Lesser Antilles, Madagascar, and Reunion. Eunectes is found in tropical South America from Colombia to Argentina. Corallus occurs in Central America from Honduras south to the Amazon drainage in eastern Bolivia and Brazil; it is found on numerous islands in the West Indies. One species of Epicrates is widespread from southern Central America and South America to Argentina; the other species are distributed throughout the West Indies. Candoia is distributed in the Indo-Pacific region from Sulawesi and the Moluccas, New Guinea, Bismarck Archipelago, Melanesia, and Polynesia east to American Samoa.
Of the Erycinae, Charina is found in western North America, including southwestern Canada, western United States, and northwestern Mexico. Charina also occurs in tropical central Africa, from Liberia east to Cameroon, Gabon, and Congo and into Zaire. In Africa, Eryx occurs in the Sahel region from Mauritania and Senegal to Kenya and Tanzania, northeastern Africa, coastal northern Africa, and the Arabian Peninsula; it also occurs in southeastern Europe, the Middle East, and Asia Minor to central Asia, India, and Sri Lanka.
Habitat
Boas can be found in nearly every habitat known to host snakes of any sort, except marine habitats. Many of the sand-boas, such as the Arabian sandboa, are well adapted to live in extremely hot and dry habitats; in contrast, Eryx tataricus is found in a very cold climate in southern Mongolia. The range of the viper boa, Candoia aspera, includes New Ireland in the Bismarck Archipelago, one of the rainiest locales on Earth. The wide-ranging boa constrictor can be found in the Sonoran Desert in northwestern Mexico, the rainforest in Brazil, and the temperate grasslands of northern Argentina.
Behavior
Boid snakes tend to be nocturnal, but they are often encountered moving or basking during the day. Faced with a perceived threat, the larger boid snakes typically defend themselves with cloacal discharge, hissing, striking, and biting. When threatened, many sandboas are reluctant to bite and instead roll into a tight ball with their heads in the center; several of the blunt-tailed species then will use their tails to mimic their heads. C. bibroni has been seen to flatten the head and the anterior half of the body, much in the manner of a cobra.
Feeding ecology and diet
Boid snakes are primarily ambush hunters that consume vertebrate prey. Ambush techniques range from that of sand-boas, which lie buried in wait for lizards or small mammals, to that of Amazon tree boas perching in trees over watercourses waiting for birds to fly by; to that of Puerto Rican boas, Epicrates inornatus, which sit high in cave entrances to intercept bats. Boid snakes can and do incorporate active foraging behavior as well.
Many small boid snakes consume lizards, both small taxa and the young of larger taxa. Anoline lizards are the favored food of many of the West Indian Epicrates. Mammals become an increasingly significant percentage of the diet as boas grow in size. Most species will consume birds whenever the opportunity presents itself. Snakes are included in the diet of anacondas, but in general snake-eating appears to be rare in the Boidae. Boas in the genera Boa and Corallus are known to caudal lure by wriggling the distal portion of their tails to attract prey. Although it does not appear to be well documented, there are a sufficient number of published reports that green anacondas kill and occasionally consume humans to assume that it does happen. It is not a common occurrence.
Reproductive biology
In most species the female is the larger sex. In some boid species, males will fight when competing to breed with a female, often incorporating wrestling and biting to achieve dominance. Male anacondas apparently do not engage in combat; groups of males are sometimes observed simultaneously courting one female.
All boine snakes and most erycine snakes are live-bearers. Litters of well-formed live young are born, typically all delivered within a short time. There is one record of a green anaconda delivering 82 young in one litter. A captive East African sandboa, Eryx colubrinus, produced more than 250 young, breeding 14 times in a 16-year period. The Arabian sandboa (E. jayakari), Sahara sandboa (E. muelleri), and the Calabar boa (C. reinhardtii) are oviparous and reproduce by laying eggs.
Conservation status
The rarest boa in the world is Corallus cropanii, known only from its type locality in southeastern Brazil. It receives no formal protection. More than 40 years have passed since the last specimen was collected, and though it has not been formally declared extinct, many authorities believe this is the case.
The Mona boa, Epicrates monensis, including both subspecies, E. m. granti and E. m. monensis, is listed as Endangered by the IUCN, owing to the fragmentation of habitat and populations, a low number of adults that is declining, habitat degradation, and introduced predators. A captive-breeding program for the species was begun in 1985, and there is now a self-sustaining captive population of several hundred individuals maintained in zoos. Reintroduction to former habitats was started in 1993, after rats and cats were eliminated from those areas. The reintroduced populations appear to be breeding.
The four species listed as Vulnerable by the IUCN are the Jamaican boa, Epicrates subflavus; Dumeril's boa, Boa dumerili; the Madagascar boa, Boa madagascariensis; and the Madagascar tree boa, Boa mandrita. At the time of this writing, all are believed to be stable.
Significance to humans
In general, few species in the Boidae are persecuted actively by humans. Most are too small to be of value in the skin trade. In the recent past, many boa species certainly were considered an important natural resource by indigenous peoples, but today it seems that most boas escape much human attention. Some of the larger boas still may be hunted for meat in remote areas, and body parts are used in folk medicine in some areas. There is commerce in the skins of anacondas and boa constrictors, but it does not approach the magnitude of the trade in python skins. With the exception of C. cropanii and Eryx somalicus, all of the boid species are kept in captivity. Boa constrictors, rosy boas, and East African sandboas are among the most commonly kept snake species; thousands are bred and born in captivity every year. As of 2002 all but three or four boid species have been reproduced in captivity.
Species accounts
List of Species
Boa constrictorViper boa
Emerald tree boa
Cuban boa
Green anaconda
Calabar boa
Rosy boa
East African sandboa
Boa constrictor
Boa constrictor
subfamily
Boinae
taxonomy
Boa constrictor Linnaeus, 1758, 'Indiis' (erroneous).
other common names
English: Boa constrictor, boa, redtail boa; French: Boa constricteur; German: Konigsboa, Sbgottshlangen; Spanish: Mazacuata, travaganado, macuarel, darura; Portuguese: Jibóia.
physical characteristics
This is a medium-size to large species with a large head distinct from the neck, a laterally compressed body, and a long prehensile tail. Throughout the extensive range, there is considerable variation in pattern and color, but most boas are brown snakes with dark brown markings on the back that expand to become red, reddish brown, or dark brown blotches on the tail.
distribution
This species is found within 150 mi (240 km) of the U.S. border in northwestern and northeastern Mexico. The range includes Mexico, Central America, most of South America north of 35° south latitude. It also occurs on Dominica and Saint Lucia in the Lesser Antilles and on many small islands along the coasts of Mexico, Central America, and South America.
habitat
This adaptable species can be found in desert, grasslands, and forest.
behavior
Boas often spend much of their time in trees. Large specimens are probably more terrestrial in their habits, but even very large boas are known to climb. Boas seek shelter in the burrows of agoutis, pacas, and armadillos.
feeding ecology and diet
Boas are primarily ambush hunters. There are records of large specimens consuming ocelots and porcupines, but the typical prey includes rodents, such as rats, squirrels, agoutis, and pacas, as well as birds, monkeys, and bats. They eat large lizards, including ameivas, tegus, and iguanas. In captivity boa constrictors typically are fed mice and rats.
reproductive biology
Little is known about reproduction in the wild. In captivity boas can become sexually mature in their second year, but maturity more typically comes in the third or fourth year. Babies usually are born 120–145 days after ovulation.
conservation status
There are no baseline data regarding wild boa populations, but the species appears to be holding its own throughout its range.
significance to humans
In agricultural areas boa constrictors are important predators of rodents. Boa constrictors are commonly kept in captivity, especially in North America and Europe.
Viper boa
Candoia aspera
subfamily
Boinae
taxonomy
Candoia aspera Günther, 1877, Duke of York Island, Bismarck Archipelago.
other common names
English: New Guinea ground boa, Papuan ground boa; French: Boa nain; German: Pazifik Boa.
physical characteristics
This is a short, heavy-bodied boa with a very short tail. The head is triangular and distinct from the neck. All of the dorsal scales are keeled with a prominent, raised, longitudinal ridge that runs down the center of each scale. The maximum length of this species approaches 3 ft (1 m), but most adults are only about half that size.
distribution
The species inhabits New Guinea and the Bismarck Archipelago.
habitat
Viper boas have been encountered in coconut husk piles, on the coast under driftwood, in trees, and in leaf litter on forest floors. They often are found in swampy areas and mudflats.
behavior
This snake is nocturnal and secretive and is rarely encountered during the day except after rain. It is known to coil in a ball for defense. It also can deliver a painful bite. It is believed that this snake mimics the death adder, Acanthophis sp., in areas where the two are sympatric.
feeding ecology and diet
Viper boas commonly feed on frogs and lizards. Small mammals also are taken.
reproductive biology
Little is known about reproduction in nature. Captured gravid females have delivered litters of five to 15 babies.
conservation status
Not threatened.
significance to humans
None known.
Emerald tree boa
Corallus caninus
subfamily
Boinae
taxonomy
Corallus caninus Linnaeus, 1758, 'Americae.'
other common names
French: Boa canin, boa émeraude; German: Grüner Hundskopfshlinger; Spanish: Falsa mapanare verde, boa esmeralda; Portuguese: Arara bóia, cobra verde.
physical characteristics
This is a beautiful green snake highly adapted for an arboreal life. The emerald tree boa has a large head with prominently
pitted labial scales. The body is elongate and very laterally compressed, and the tail is long and very prehensile. This species has the longest teeth of any nonvenomous snake; the front teeth of a large specimen can be 1.5 in (3.7 cm) in length.
distribution
This species is known from the tropical rainforests in and surrounding the Amazon Basin of South America.
habitat
This species is associated with primary and secondary forest. It is often found in trees overhanging or near water courses.
behavior
The resting pose of this species appears to be a flat coil that is folded over a branch, with the head in the center pointing down as if to watch below.
feeding ecology and diet
Rodents, parrots, passerines, and small monkeys have all been recorded as prey.
reproductive biology
Babies are red, orange, or green. They change to the adult green color as they approach sexual maturity.
conservation status
Many Latin American countries control or forbid the export of native boid snakes; emerald tree boas thereby receive some protection from commercial collecting in most of the countries where the species occurs. The species appears to be stable and not threatened, but its future is tied to the forests it inhabits.
significance to humans
This attractive snake is popular among keepers of boas. The species is hardy in captivity and is regularly bred in captivity.
Cuban boa
Epicrates angulifer
subfamily
Boinae
taxonomy
Epicrates angulifer Bibron, 1840, Cuba.
other common names
French: Boa de Cuba; German: Kuba-Schlankboa; Spanish: Majá de Santa Maria.
physical characteristics
This is the largest species in the genus Epicrates, with a maximum size approaching 13 ft (4 m).
distribution
E. angulifer is found throughout Cuba at altitudes up to 1,000 ft (310 m); the species also occurs on nearby smaller islands.
habitat
This is an adaptable snake most often found in wooded areas, often off the ground in trees but also on rocky hillsides, in caves, and in talus.
behavior
Captive juvenile Cuban boas tend to be excitable and irritable, often biting their keepers when given the chance; adults tend to be calm and placid animals that do well in captivity. Like most boas in the genus Epicrates, the Cuban boa often excretes viscous liquid uric acid (white insoluble nitrogenous waste products) when excited or frightened.
feeding ecology and diet
Cuban boas are both ambush predators and active foragers. They are known to eat bats, rodents, chickens, native birds, and iguanas.
reproductive biology
Males fight during the breeding season. Females deliver litters of two to 10 large babies that are up to 24 in (61 cm) in length.
conservation status
Not threatened. Cuban boas are protected by Cuban law, and are believed to be common throughout Cuba. The species seems to coexist well with humans when it is not persecuted.
significance to humans
This species occasionally preys on domestic fowl.
Green anaconda
Eunectes murinus
subfamily
Boinae
taxonomy
Eunectes murinus Linnaeus, 1758, 'America.'
other common names
English: Water boa; huilla, huilia, camoudi; French: Anaconda commun; German: Grosse Anakonda; Portuguese: Arigbóia, boiuna, boicu, boiguacu, sucuri, sucuriju, sucurijuba, Spanish: Culebra de agua.
physical characteristics
This is a giant, heavy-bodied, dark green boa with black spots. Even an average specimen, 10–15 ft (3–4.6 m) in length, appears immense because of its girth.
distribution
This species occurs in the Amazonian and Orinoco drainages from Columbia and Venezuela to eastern Bolivia and central Brazil. It also is known from Trinidad.
habitat
The green anaconda is associated strongly with watercourses, swamps, and other freshwater habitats.
behavior
Anacondas are rarely found far from water. Feeding usually takes place in the water.
feeding ecology and diet
Anacondas typically lie in wait for prey at the water's edge. They are known to eat a wide variety of vertebrate prey, including monkeys, deer, peccaries, pacas, agoutis, birds, fish, caiman, and turtles.
reproductive biology
Breeding usually occurs during the dry season. A group of males will court a receptive female, competing peacefully to copulate.
conservation status
Not threatened. So far as is known, the green anaconda exists in reasonable numbers throughout its range.
significance to humans
Anacondas seem to be largely unmolested by humans. They are not commonly harvested for meat, and throughout most of the range there is little or no harvest of skins. Small specimens are collected and exported for the live trade, but the species is not particularly popular in captivity, largely because of its size but in part because many specimens are foul-tempered.
Calabar boa
Charina reinhardtii
subfamily
Erycinae
taxonomy
Charina reinhardtii Schlegel, 1848, originally designated as 'Old Calabar, West Africa' and now annotated to 'Gold Coast.'
other common names
English: Burrowing python, Calabar ground python; German: Erdpython.
physical characteristics
The Calabar boa is a small species that only rarely grows longer than 30 in (80 cm). The head is small and not distinguished from the neck. The body is round, the skin is soft, the scales are smooth, and the tail is blunt. Individuals are dark brown or black with red or orange scales randomly scattered on the body. Hatchlings have white markings on their tails that disappear with age.
distribution
The species occurs in west and central Africa from Guinea and Liberia east to Cameroon, Gabon, Congo, and into Zaire.
habitat
The Calabar boa is associated with forest, soft soil, and leaf litter. It most often is seen out and moving after rains, both during the day and at night.
behavior
Calabar boas form a tight ball with the head in the middle and use the tail as a decoy. The tail of wild adults usually is scarred. So strong is the instinct for this defensive behavior that even captive-hatched and raised animals rarely will uncoil when handled. This species never bites in defense.
feeding ecology and diet
In nature the diet includes rodents and insects. In captivity the species eats rodents at all ages.
reproductive biology
The Calabar boa is oviparous; relative to body size, the eggs are immense. The eggs are delicate and thin-shelled. Clutch size ranges from one to 12 eggs; most clutches number two to four eggs.
conservation status
Not known.
significance to humans
It is reported that this species is feared by some local people, who believe that it has two heads.
Rosy boa
Charina trivirgata
subfamily
Erycinae
taxonomy
Charina trivirgata Cope, 1861, Cape San Lucas, Baja California Sur, Mexico.
other common names
French: Boa à trois bandes; German: Deistreifen-Rosenboa.
physical characteristics
The rosy boa is a small, heavy-bodied snake with a small head that is barely distinct from the neck. The eyes are small, and the pupils are vertical. The tail is relatively long and thick, coming to a blunt point. The scales are smooth and shiny. Large specimens attain considerable bulk and girth. Adult females are about 28–36 in (71–95 cm) in total length; most adult males are 18–26 in (46–67 cm). The maximum size of this form approaches 4 ft (1.3 m).
distribution
The species ranges across southern California, southwestern Arizona, and northwestern Mexico.
habitat
This is a saxicolous species, strongly associated with rocky canyons and rocky ridges and hills.
behavior
Rosy boas are usually docile snakes that are deliberate in their actions and reluctant to bite in defense.
feeding ecology and diet
Small rodents and lizards make up the bulk of the diet.
reproductive biology
A gravid female will complete a shed 16–20 days after ovulation. Usually babies are born 100–120 days after that shed. Litters typically are born from mid-August to early October. Clutch size is reported to vary from one to 13; most litters number four or five.
conservation status
Not threatened.
significance to humans
This is a very popular snake species in captivity; every year, thousands of captive-bred rosy boas are born.
East African sandboa
Eryx colubrinus
subfamily
Erycinae
taxonomy
Anguis colubrinus Linnaeus, 1758, 'Egypto.'
other common names
French: Boa des éscailles rugueuses; German: Aegyptische Sandboa, Kenyan Sandboa.
physical characteristics
This is a heavy-bodied sandboa with a maximum length that approaches 36 in (90 cm). The northern populations are smaller and patterned in tan and yellow, whereas the southern populations are larger and darker with an orange pattern. The undersurface is an immaculate white. The dorsal surface of the tail is armored with thick skin and hooked keeled scales.
distribution
The species is distributed in northeast Africa from central Tanzania north to Egypt and from there west into Niger.
habitat
In the northern part of the range this species is more likely found in arid sandy and rocky areas; to the south these sand-boas are found in rocky hills and in burrows in soil. They often occupy agricultural fields.
behavior
This sandboa rarely strikes forward in defense, but it defends itself with quick backward-directed slashes when its body is touched.
feeding ecology and diet
In captivity the larger animals from southern populations feed on rodents at all ages; the northern animals more often feed on geckos and skinks when they are young.
reproductive biology
Most litters contain 12–20 babies, but litters of 32 babies are reported.
conservation status
Nothing is known about this species in nature.
significance to humans
This is a very popular snake to keep in captivity; thousands of babies are born in captivity annually. The captive specimens constitute a viable self-sustaining population; very few East African sandboas are taken from the wild.
Resources
Books
de Vosjoli, Philippe, Roger Klingenberg, and Jeff Ronne. The Boa Constrictor Manual. Santee, CA: Advanced Vivarium Systems, 1998.
Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.
Minton, Sherman A., and Madge Rutherford Minton. Giant Reptiles.New York: Charles Scribner's Sons, 1973.
Murphy, John C., and Robert W. Henderson. Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons. Malabar, FL: Krieger Publishing Company, 1997.
O'Shea, Mark. A Guide to the Snakes of Papua New Guinea.Port Moresby, Papua New Guinea: Independent Publishing, 1996.
Pope, Clifford Millhouse. The Giant Snakes: The Natural History of the Boa Constrictor, the Anaconda, and the Largest Pythons, Including Comparative Facts About Other Snakes and Basic Information on Reptiles in General.New York: Alfred A. Knopf, 1961.
Stafford, Peter J., and Robert W. Henderson. Kaleidoscopic Tree Boas: The Genus Corallus of Tropical America. Malabar, FL: Krieger, 1996.
Stebbins, Robert C. A Field Guide to the Western Reptiles and Amphibians: Field Marks of All Species in Western North America, Including Baja California. 2nd edition. Boston: Houghton Mifflin, 1985.
Tolson, P. J., and R. W. Henderson. The Natural History of West Indian Boas. Taunton, England: R & A Publishing Limited, 1993.
Periodicals
Kluge, Arnold G. 'Boine Snake Phylogeny and Research Cycles.' Miscellaneous Publications, Museum of Zoology, University of Michigan, no. 178 (1991): 1–58.
——. 'Calabaria and the Phylogeny of Erycine Snakes.' Zoological Journal of the Linnean Society 107 (1993): 293–351.
McDowell, S. B. 'A Catalogue of the Snakes of New Guinea and the Solomons, with Special Reference to Those in the Bernice P. Bishop Museum. Part III. Boinae and Acrochordoidea (Reptilia, Serpentes).' Journal of Herpetology 13, no. 1 (1979): 1–92.
David G. Barker, MS
Tracy M. Barker, MS
AbstractBoids are primitive snakes from a basal lineage that is widely distributed in Neotropical region. Many of these species are both morphologically and biogeographically divergent, and the relationship among some species remains uncertain even with evolutionary and phylogenetic studies being proposed for the group. For a better understanding of the evolutionary relationship between these snakes, we cytogenetically analysed 7 species and 3 subspecies of Neotropical snakes from the Boidae family using different chromosomal markers. The karyotypes of Boa constrictor occidentalis, Corallus hortulanus, Eunectes notaeus, Epicrates cenchria and Epicrates assisi are presented here for the first time with the redescriptions of the karyotypes of Boa constrictor constrictor, B.
Amarali, Eunectes murinus and Epicrates crassus. The three subspecies of Boa, two species of Eunectes and three species of Epicrates exhibit 2n = 36 chromosomes. In contrast, C. Hortulanus presented a totally different karyotype composition for the Boidae family, showing 2n = 40 chromosomes with a greater number of macrochromosomes. Furthermore, chromosomal mapping of telomeric sequences revealed the presence of interstitial telomeric sites (ITSs) on many chromosomes in addition to the terminal markings on all chromosomes of all taxa analysed, with the exception of E. Thus, we demonstrate that the karyotypes of these snakes are not as highly conserved as previously thought. Moreover, we provide an overview of the current cytotaxonomy of the group.
Citation: Viana PF, Ribeiro LB, Souza GM, Chalkidis HdM, Gross MC, Feldberg E (2016) Is the Karyotype of Neotropical Boid Snakes Really Conserved? Cytotaxonomy, Chromosomal Rearrangements and Karyotype Organization in the Boidae Family. PLoS ONE 11(8):e0160274.Kunbo Wang, Institute of Cotton Research of Chinese Academy of Agricultural Sciences, CHINAReceived: January 18, 2016; Accepted: July 15, 2016; Published: August 5, 2016Copyright: © 2016 Viana et al. This is an open access article distributed under the terms of the, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Data Availability: All relevant data are within the paper.Funding: This work was supported by the Pronex/FAPEAM/CNPq 003/2009 (to EF) and MCT/CNPq/MEC/CAPES/FNDCT – Cross Action/FAPs No. 47/2010 – BioPHAM Network, and the CAPES – Pro-Amazon Program: Biodiversity and Sustainability, Public Notice No. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. George Myller Souza is employed by Criadouro Comercial Jiboias Brasil.
Criadouro Comercial Jiboias Brasil provided support in the form of salary for author GMS, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section.Competing interests: George Myller Souza is employed by Criadouro Comercial Jiboias Brasil.
There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials. Species/subspecies studied, location, gender and number of analysed individuals.Analysis of the constitutive heterochromatin was performed following the protocol described by Sumner with some modifications. Samples were treated with 0.2 N hydrochloric acid (HCl) at 45°C for 2 minutes and with 5% alkali barium hydroxide (Ba(OH) 2) at 45°C for 1 minute. Then, the samples were treated with a saline sodium citrate solution (2X SSC) at 60°C for 30 minutes.
Finally, the samples were stained with 5% Giemsa for 5 minutes. The detection of ribosomal active sites was performed according to the protocol described by Howell and Black with some modifications. The samples were pretreated with 0.2 N HCl for 5 minutes at room temperature and then stained with AgNO 3 for 5 minutes at 45°C. FISH was conducted according to the protocol described by Pinkel et al.
with modifications using 77% stringency (2.5 ng/μl of DNA, 50% deionized formamide, 10% dextran sulfate, and 2X SSC at 37°C for 24 h). The slides were counter-stained with 4',6-diamidino-2-phenylindole (DAPI). We used homologous probes for 18S rDNA and telomeric probes labelled with digoxigenin-11-dUTP (Dig-Nick Translation Mix, Roche). Boa karyotypes.Karyotype of Boa constrictor constrictor with conventional staining (a), nucleolar organizer regions and location of the 18S rDNA (b), and C-banding (c); karyotype of Boa constrictor amarali with conventional staining (d), nucleolar organizer regions and location of the 18S rDNA (e), and C-banding (f); karyotype of Boa constrictor occidentalis with conventional staining (g), nucleolar organizer regions and location of the 18S rDNA (h), and C-banding (i).The C. Hortulanus samples had 2n = 40 chromosomes, the karyotype formula 4m+16st+20mi and an NF equal to 60, with no sex chromosome heteromorphisms. Amazon tree boa and anaconda karyotypes.Karyotype of Corallus hortulanus with conventional staining (a), nucleolar organizer regions and location of the 18S rDNA (b), and C-banding (c); karyotype of Eunectes murinus with conventional staining (d), nucleolar organizer regions and location of the 18S rDNA (e), and C-banding (f); karyotype of Eunectes notaeus with conventional staining (g), nucleolar organizer regions and location of the 18S rDNA (h), and C-banding (i).The E. Murinus and E.
Notaeus samples had 2n = 36 chromosomes, the karyotype formula 6m+2sm+8st+20mi and an NF equal to 52, with no sex chromosome heteromorphisms or differences observed among animals from different locations.The E. Assisi and E. Crassus samples had 2n = 36 chromosomes, the karyotype formula 6m+2sm+8st+20mi and an NF equal to 52, with no sex chromosome heteromorphisms. Constitutive heterochromatinThe distribution of C bands was primarily evident in the macrochromosomes of all individuals analysed, and a distinct pattern was observed for each species/subspecies analysed. The microchromosomes showed diffuse markings.
No differences in the C-banding patterns were found among samples from different locations or between males and females.The subspecies B. Constrictor presented heterochromatic blocks in pairs 2, 4, 5, 7 and 8 ; B. Amarali presented heterochromatic blocks in pairs 2, 4, 7 and 8 ; and B. Occidentalis presented heterochromatic blocks in pairs 2, 4 and 5.In C. Hortulanus, heterochromatic blocks were evident in all macrochromosomes (1–20), with bitelomeric, interstitial and centromeric markings.In the anacondas ( E. Murinus and E.
Notaeus), heterochromatic blocks were also evident in all macrochromosomes (1–16), with bitelomeric, interstitial and centromeric markings. In both species, the chromosome 1 pair showed high similarity, with an interstitial heterochromatic block on the short arm, 2 interstitial blocks on the long arm and bitelomeric markings; however, variations in the distribution and quantity of these heterochromatic blocks were very evident between the 2 species.In the rainbow boas ( E. Assisi and E. Crassus), we also found evident heterochromatic blocks in all macrochromosomes (1–16), with bitelomeric, interstitial and centromeric markings. Telomeric sequencesChromosomal mapping of the telomeric sequences revealed the presence of terminal markings on all chromosomes of all taxa analysed as well as the presence of ITSs. The exception was E.
Notaeus, in which no trace of an ITS was detected.B. Constrictor presented ITSs in chromosome pairs 2 and 4 , B. Amarali in pairs 1, 2 and 6 , and B. Occidentalis in pairs 2, 4 and 8. Hortulanus presented ITSs in pair 2 , whereas E. Murinus presented ITSs in pairs 1, 2 and 6. Furthermore, E.
Cenchria presented ITSs only in pair 2 in the short arm , whereas E. Assisi presented ITSs in pairs 1 and 2.
Crassus also presented ITSs only in pair 2. Phylogenetic relationships of the Boidae family (genera Boa, Corallus, Eunectes and Epicrates), with representation of the diploid numbers and karyotype formulas in ideograms (topology follows ).The snakes C. Hortulanus and C. Caninus have the highest diploid numbers in the Boidae family, with 40 and 44 chromosomes, respectively (, this study).
The apomorphy detected in Corallus (2n = 40 in this study and 2n = 44 in ) may have originated from fissions in the macrochromosomes from the common ancestor among Corallus, Eunectes and Epicrates.To date, the karyotypes of only 2 species of the Corallus genus have been described: C. Caninus, with a karyotype consisting of 44 basically acrocentric chromosomes , and another species previously known as Corallus enhydris cookii from the island of Grenada in the West Indies, with a karyotype of 2n = 40 chromosomes, which was observed in a female snake. The latter species ( C. Cookii) was synonymized with C. Hortulanus years later, which led us to believe that the specimen whose karyotype was described in the work by Gorman and Gress was actually a specimen of C. Grenadensis endemic to the island of Grenada; this species was maintained as a synonym of C.
Hortulanus for a long period of time. Thus, using molecular techniques, Coulston et al. challenged the validity of C. However, Reynolds et al.
and Pyron et al. provided strong support for the validity of this species. Furthermore, Gorman and Gress reported a karyotype of 2n = 40, 4m+16a+20mi, and NF = 44 ♀ for C. Grenadensis, which was significantly different from the karyotype of C. Hortulanus described in the present work in terms of the fundamental number and karyotype formula (2n = 40, 6m+16st+18mi, and NF = 62 ♀).
Therefore, we consider that this is the first karyotypic description of C. Hortulanus from South America. Variations in the ribosomal regions and 18S rDNA sequences in snakesThe number of nucleolar markings and their locations on a pair of microchromosomes demonstrated by Ag-NOR staining and 18S rDNA sequences can be considered conserved features among snakes of the basal lineage and plesiomorphic features of several families of snakes with 2n = 36 chromosomes, including 16 macrochromosomes and 20 microchromosomes ,.
In contrast, there is great variation in the locations of these markings among some snakes of derived lineages, which may be present on macrochromosomes, microchromosomes and even sex chromosomes ,. These variations in the locations of rDNA sites have been well documented for the species Bothrops neuwiedi , in which rDNA is present in both the microchromosomes and macrochromosomes in different populations. This characteristic supports the hypothesis proposed by Camper and Hanks , who suggested that translocation rearrangements occurred between the macrochromosomes and microchromosomes, which in this case changed the location of the nucleolar region while the number of microchromosomes remained the same.These variations were also reported by Porter et al. , who identified variability in the locations of ribosomal sites using FISH with 28S rDNA probes in several snake species from different families.
Thamnophis marcianus (Natricidae) and Coluber flagellum (Colubridae) were found to have simple markings on macrochromosomes, whereas Crotalus viridis (Viperidae) presented multiple markings on 2 pairs of microchromosomes. A similar pattern was evident in Bothrocophias hyoprora (Viperidae) from the Amazon region, which was found to have multiple markings on 2 pairs of microchromosomes based on staining with AgNO 3. Additionally, staining with AgNO 3 together with 18S rDNA mapping using homologous probes allowed the identification of simple markings on a single pair of macrochromosomes in Spilotes sulphureus (Colubridae). No association of rDNA with the sex chromosomes of this species was detected (unpublished data). These characteristics (NOR, 18S and 28S rDNA) along with simple markings of a pair of macrochromosomes and multiple markings of both macrochromosomes and microchromosomes are typical peculiarities of snakes belonging to intermediate and derived lineages. Telomere-specific patterns and chromosomal rearrangements in Neotropical boid snakesTo date, no mapping of telomeric sequences or traces of ITSs indicative of chromosomal rearrangements have been identified in representative species of the Boidae family.In our study, we demonstrated patterns that distinguished each species/subspecies.
Additionally, we performed chromosomal mapping of telomeric sequences and revealed the notable occurrence of various ITSs, which were evident in the macrochromosomes of the 3 subspecies of B. Constrictor, C. Hortulanus, and E. Murinus and the 3 species of Epicrates; these ITSs may be indicative of chromosomal rearrangements. These findings suggest that ITSs may not necessarily randomly occur in Boidae snakes but may represent an independent evolutionary history for each genus.The ITSs present among the various orders of vertebrates have different origins –.
For example, ITSs may arise due to the activity of telomerase in repairing chromosomal breaks by adding telomeric sequences to non-terminal regions resulting from fusions, fissions, inversions or even duplications of these sequences ,. For example, duplications appear to have occurred in the last macrochromosome pair of B.
Occidentalis and in pair 2 of C. The ITS present in pair 2 (st) of C. Hortulanus may be indicative of an inversion, followed by the duplication of (TTAGGG)n fragments. This ITS would be equivalent to the pairs of submetacentric macrochromosomes maintained in Boa, Eunectes and Epicrates because the ITS was associated with a heterochromatic region, and there was an ITS at an interstitial position on the short arm of pair 2 (sm) in all analysed boid snakes, with the exception of E.
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Notaeus.In some groups, there is an apparent distribution pattern of telomeric motifs, which may indicate a common evolutionary history between sister clades, such as Eunectes and Epicrates. The mapping of telomeric sequences in E. Cenchria and E. Crassus revealed that these species had very similar compositions, including identical ITS patterns. Interestingly, despite the similar distribution patterns of telomeric sequences, E. Cenchria and E.
Crassus appear to exhibit patterns that are more similar to those of Eunectes than to those of the Boa subspecies, especially because E. Notaeus does not possess ITSs.Notably, the presence of ITSs is common in squamates. These sites may be considered common even in basal clades, such as the family Boidae (this study), highlighting the role of the dynamics of chromosomal rearrangements in the diversity of this group. However, we believe that not all ITSs found in the snakes analysed here are necessarily indicative of chromosomal rearrangements because not all of them are associated with constitutive heterochromatin, although it is highly probable that they are associated with transposable elements or satellite DNA. In contrast, no correlation was detected between the ITSs of the species Eunectes murinus and the non-long terminal repeat (LTR) retrotransposon Rex6 (unpublished data). Although not all of the ITSs located in pair 2 (sm) of Boa, Eunectes and Epicrates are associated with heterochromatin, it is very likely that these ITSs are indicative of chromosomal rearrangements and that they are a result of recent events.Further study is needed to determine whether other repetitive elements are associated with the ITSs found in these snakes and to uncover the real reason why some species are susceptible to the accumulation of these sequences in their chromosomes.
ConclusionsThe data obtained in this study increase our understanding of the cytotaxonomy of Neotropical Boidae snakes. Specific chromosomal characteristics were identified for each taxa, revealing that the karyotypes of these snakes were not as conserved as previously thought. Our study is the first to identify ITSs in the Boidae family and superfamily Booidea as well as in Henophidia snakes. These findings suggest that chromosomal rearrangements have contributed to the diversification of the group. We also conclude that ITSs are common in basal and derived lineages within the suborder Serpentes. Thus, our study significantly contributes to current knowledge regarding the taxonomy and karyotype organization of the group.