Three-toed sloth

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Three-toed sloths[1]
Brown-throated three-toed sloth
(Bradypus variegatus)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Superfamily:
Megatherioidea
Family: Bradypodidae
Gray, 1821
Genus: Bradypus
Linnaeus, 1758
Type species
Bradypus tridactylus
Species

5, see text

Green: B. pygmaeus, blue: B. tridactylus, red: B. variegatus, yellow: B. torquatus, orange: B. crinitus

The three-toed or three-fingered sloths are

Megatherioidea, making them the only surviving members of that radiation.[2][3]

Extant species

Image Scientific name Common name Distribution
B. pygmaeus Pygmy three-toed sloth Isla Escudo de Veraguas (Panama)
B. torquatus Maned sloth Atlantic coastal rainforest of southeastern Brazil
B. tridactylus Pale-throated sloth Part of northern South America, including Guyana, Suriname, French Guiana, eastern Venezuela and Brazil north of the Amazon River
B. variegatus Brown-throated sloth Central America and much of north and central South America, from Honduras through Colombia, Venezuela, Ecuador, eastern Peru, Bolivia and Brazil
B. crinitus Southern maned sloth Coastal Brazil in Rio de Janeiro and Espirito Santo.[4]

Evolution

A study of mitochondrial cytochrome b and 16S rRNA sequences suggests that B. torquatus diverged from B. variegatus and B. tridactylus about 12 million years ago, while the latter two split 5 to 6 million years ago. The diversification of B. variegatus lineages was estimated to have started 4 to 5 million years ago.[5]

Relation to the two-toed sloth

Both types of

Caribbean sloths.[7]

Understanding of sloth phylogeny has recently been greatly revised by molecular studies, based on

mylodontids, while moving the Caribbean sloths to a separate, basal branch of the sloth evolutionary tree.[3][2]
These results provide further strong support for the long-held belief that arboreality arose separately in the two genera via convergent paths.

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al., 2019).[3]

Folivora

† Megalocnidae (Caribbean sloths)

Mylodontoidea

† Scelidotheriidae

† Mylodontidae

   

Choloepodidae
(two-toed sloths)

Megatherioidea
† Megalonychidae

† Megalonyx jeffersoni

Bradypodidae

Bradypus torquatus

Bradypus pygmaeus

Bradypus tridactylus

Bradypus variegatus

(three-toed sloths)

Characteristics

Famously slow-moving, a sloth travels at an average speed of 0.24 km/h (0.15 mph).

quadrupeds
.

Behavior

Like the two-toed sloth, three-toed sloths are agile swimmers. They are still slow in trees.[10] The muscles that sloths use to grip and produce a pulling motion are much more prominent than those that produce a pushing motion.[11] This means that they struggle to support their body weight when walking on all four limbs, so traveling on the ground is a dangerous and laborious process.[12]

Three-toed sloths are arboreal (tree-dwelling), with a body adapted to hang by their limbs. Large, curved claws and muscles specifically adapted for strength and stamina help sloths to keep a strong grip on tree branches.[13] The abdominal organs close to their diaphragm (such as their stomach, liver, and kidneys) are attached to their lower ribs (or pelvic girdle in the latter case) by fibrinous adhesions, which prevent the weight of these organs from compressing their lungs when hanging, making inhalation easier.[14]

They live high in the canopy but descend once a week to defecate on the forest floor. During this week-long interval, their feces and urine accumulate to about a third of their total body mass.[14] It takes about a month for a single leaf to pass through its four-chambered stomach and digestive tract.[15] Although they get most of their fluids from the leaves that they eat, they have been observed drinking directly from rivers.[16] Because of their slow metabolism, they do not need to ingest many leaves on a daily basis, but when ambient temperatures are high, the symbiotic microbes and bacteria present in their gut will break down and ferment food at a faster rate.[17] Conversely, when temperatures are lower, sloths will consume less, which is opposite to what has been observed in most other mammals.[15] Only very few species of sloths are found at higher altitudes, and these are found to have thicker coats than those living in lower altitudes. Some of the extinct species of sloths were able to tolerate cooler temperatures, but researchers believe this was probably due to thicker fur, larger size, larger muscle mass, and more access to a constant food supply.[18]

Their long, coarse fur often appears greenish, due not to pigment, but to algae growing on it. Sloths' greenish color and their sluggish habits provide an effective camouflage; hanging quietly, sloths resemble a bundle of leaves.

They move between different trees up to four times a day, although they prefer to keep to a particular type of tree, which varies between individuals, perhaps as a means of allowing multiple sloths to occupy overlapping home ranges without competing with each other.[19]

Three-toed sloths are predominantly

nocturnal.[20]

Biology

Lifecycle

Three-toed sloth crossing a road in Alajuela, Costa Rica

Members of this genus tend to live around 25 to 30 years, reaching sexual maturity at three to five years of age. Three-toed sloths do not have a mating season but breed year-round.

Male three-toed sloths are attracted to females in

estrus by their screams echoing throughout the canopy. Sloth copulation lasts an average of 25 minutes.[21] Male three-toed sloths are strongly polygamous and exclude competitors from their territory. Males are also able to compete with one another within small habitable territories.[22] Females give birth to a single young after a gestation period of around six months. The offspring cling to their mother's bellies for around nine months. They are weaned around nine months of age when the mother leaves her home territory to her offspring and moves elsewhere. Adults are solitary, and mark their territories using anal scent glands and dung middens.[19]

The home ranges used by wild

riparian forests, peri-urban areas, and living fence-rows.[23] For the first few months after giving birth, mothers remain at just one or two trees and guide their young. At about five to seven months of age, when the young have become more independent, mothers expand their resources and leave their young in new areas. During natal dispersion, three-toed sloths prefer tropical forests, often using riparian forest habitat to disperse while avoiding pastures and shade-grown cacao.[24] The home range for mothers is larger than those of young. After separation, only the mothers use the cacao-growing forest, but both use riparian forests. Different types of trees are used by both mother and young, which indicates that this agricultural matrix provides an important habitat type for these animals.[25]

Dentition and skeleton

Three-toed sloths have no

canine teeth, just a set of peg-shaped cheek teeth that are not clearly divided into premolars and molars, and lack homology with those teeth in other mammals, and thus are referred to as molariforms. The molariform dentition in three-toed sloths is simple and can be characterized as dental formula of: 54-5.[26]

Three-toed sloths are unusual amongst

homeotic genes.[27] All other mammals have seven cervical vertebrae,[28] other than the two-toed sloth and the manatee
, which have only six.

Microbial ecology

Three-toed sloths use their gut

Proteobacteria are the main bacterial phyla that dominate the sloth gut microbiome, which is less diverse than in many other herbivores. Not only are Firmicutes bacteria found in feces and digesta, but they are also found externally on the fur of sloths. Some research has found that Firmicutes bacteria in the genera Brevibacterium and Rothia can secrete antibiotic compounds that may provide protection from pathogenic bacteria.[30]

References

  1. OCLC 62265494
    .
  2. ^ a b c d Delsuc, F.; Kuch, M.; Gibb, G.C.; Karpinski, E.; Hackenberger, D.; Szpak, P.; et al. (2019). "Ancient Mitogenomes reveal the evolutionary history and biogeography of sloths". Current Biology. 29 (12): 2031–2042.e6.
    PMID 31178321
    .
  3. ^
    S2CID 174813630. Archived
    (PDF) from the original on 12 September 2020. Retrieved 18 September 2020.
  4. doi:10.1093/jmammal/gyac059
    .
  5. doi:10.1644/10-MAMM-A-086.1
    .
  6. PMID 8552600
    .
  7. ^ White, J.L.; MacPhee, R.D.E. (2001). "The sloths of the West Indies: a systematic and phylogenetic review". In Woods, C.A.; Sergile, F.E. (eds.). Biogeography of the West Indies: Patterns and perspectives. Boca Raton, FL / London, UK / New York, NY / Washington, DC:
    ISBN 978-0-8493-2001-9
    .
  8. ^ "Speed of Animals". infoplease.com.
  9. doi:10.1002/9780470385005.ch12
  10. ^ Three-toed Sloth, National Geographic.
  11. S2CID 22238582
    .
  12. ^ Keating, Ian D. (2018-01-01), Audacious Sloth, retrieved 2020-03-30
  13. S2CID 22238582
    .
  14. ^
    PMID 24759371
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  15. ^
    PMID 25861559
    .
  16. ISSN 1540-9309
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  17. PMID 25861559
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  18. PMID 11151024
    .
  19. ^
    ISBN 0-87196-871-1
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  20. OCLC 493329394
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  21. PMID 10657054
    .
  22. PMID 23284687
    .
  23. doi:10.1111/1365-2664.13138
    .
  24. ISSN 1365-2664
    .
  25. PMID 22208090
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  26. ISBN 9780801899515
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  27. ^ "Sticking Their Necks out for Evolution: Why Sloths and Manatees Have Unusually Long (or Short) Necks". May 6th 2011. Science Daily. Retrieved 25 July 2013.
  28. PMID 10327647. Archived from the original
    (PDF) on 2004-11-10.
  29. PMID 26271635
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  30. S2CID 249096251
    . Retrieved 2023-12-01.

External links

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