The Aldabra giant tortoise (''Aldabrachelys gigantea'') is a
species
In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of tortoise in the
family Testudinidae. The species is
endemic to the islands of the
Aldabra
Aldabra is the world's second-largest coral atoll, lying south-east of the continent of Africa. It is part of the Aldabra Group of islands in the Indian Ocean that are part of the Outer Islands of the Seychelles, with a distance of 1,120 k ...
Atoll in the
Seychelles
Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
. It is one of the largest
tortoises in the world.
[Pritchard, Peter C.H. (1979) ''Encyclopedia of Turtles.'' Neptune, New Jersey: T.F.H. Publications, Inc. Ltd.] Historically, giant tortoises were found on many of the western Indian Ocean islands, as well as Madagascar, and the fossil record indicates giant tortoises once occurred on every continent and many islands with the exception of Australia and Antarctica.
Many of the Indian Ocean species were thought to be driven to extinction by over-exploitation by European sailors, and they were all seemingly extinct by 1840 with the exception of the Aldabran giant tortoise on the island atoll of Aldabra.
Although some remnant individuals of ''A. g. hololissa'' and ''A. g. arnoldi'' may remain in captivity,
in recent times, these have all been reduced as subspecies of ''A. gigantea''.
Description
The
carapace
A carapace is a dorsal (upper) 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 under ...
of ''A. gigantea'' is a brown or tan in color with a high, domed shape. The species has stocky, heavily
scaled legs to support its heavy body. The neck of the Aldabra giant tortoise is very long, even for its great size, which helps the animal to exploit
tree branches up to a meter from the ground as a food source. Similar in size to the famous
Galápagos giant tortoise, its carapace averages in length with an average weight of . Females are generally smaller than males, with average specimens measuring in carapace length and weighing . Medium-sized specimens in captivity were reported as in body mass. Another study found body masses of up to most commonplace.
Nomenclature and systematics
This species is widely referred to as ''Aldabrachelys gigantea'', but in recent times, attempts were made to use the name ''
Dipsochelys
''Aldabrachelys'' is the recognised genus for the Seychelles and Madagascan radiations of giant tortoises, including the Aldabra giant tortoise (''Aldabrachelys gigantea'').
Naming
This name is problematic in that the type specimen is actually r ...
'' as ''Dipsochelys dussumieri'', but after a debate that lasted two years with many submissions, the
ICZN
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the I ...
eventually decided to conserve the name ''Testudo gigantea'' over this recently used name (ICZN 2013)
this also affected the
genus name for the species, establishing ''Aldabrachelys gigantea'' as ''
nomen protectum
In zoological nomenclature, a ''nomen oblitum'' (plural: ''nomina oblita''; Latin for "forgotten name") is a disused scientific name which has been declared to be obsolete (figuratively 'forgotten') in favour of another 'protected' name.
In its p ...
''.
Four
subspecies are currently recognized.
A
trinomial authority in parentheses indicates that the subspecies was originally described in a
genus other than ''Aldabrachelys'':
* ''A. g. gigantea'' ,
Aldabra giant tortoise from the
Seychelles
Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
island of Aldabra
* ''
A. g. arnoldi'' ,
[Bour, Roger (1982). "''Contribution à la connaisance des tortues terrestres des Seychelles: définition du genre endémique et description d'une espéce nouvelle probablement originaire des îles grantiques & bord de l'extinction''". ''Comptes Rendus de l'Académie des Sciences'' 295: 117–122. (''Dipsochelys arnoldi'', new species, p. 118). (in French).] Arnold's giant tortoise from the Seychelles island of Mahé
* ''
A. g. daudinii'' † ,
Daudin's giant tortoise, from the Seychelles island of Mahé (extinct 1850)
* ''
A. g. hololissa'' ,
Seychelles giant tortoise, from the Seychelles islands of Cerf, Cousine, Frégate, Mahé, Praslin, Round, and Silhouette
The
subspecific name, ''daudinii'', is in honor of French zoologist
François Marie Daudin
François Marie Daudin (; 29 August 1776 in Paris – 30 November 1803 in Paris) was a French zoologist.
With legs paralyzed by childhood disease, he studied physics and natural history, but ended up being devoted to the latter.
Daudin wrote ' ( ...
.
Range and distribution
The main population of the Aldabra giant tortoise resides on the islands of the
Aldabra Atoll
Aldabra is the world's second-largest coral atoll, lying south-east of the continent of Africa. It is part of the Aldabra Group of islands in the Indian Ocean that are part of the Outer Islands of the Seychelles, with a distance of 1,120 ...
in the Seychelles. The atoll has been protected from human influence and is home to some 100,000 giant tortoises, the world's largest population of the animal. Smaller populations of ''A. gigantea'' in the Seychelles exist in the
Sainte Anne Marine National Park
Sainte Anne Marine National Park lies about 5 km from Victoria, the capital city of the Seychelles, and encompasses eight small islands.
History
The Marine Park was created in 1973 for the preservation of wildlife, the first of its kind in th ...
(e.g.
Moyenne Island
Moyenne Island is a small island () in the Sainte Anne Marine National Park off the north coast of Mahé, Seychelles. Since the 1970s onwards, it has been a flora and fauna reserve. From 1915 until the 1960s, the island was abandoned until its p ...
), and on
La Digue
La Digue is the third most populated island of the Seychelles, and fourth largest by land area, lying east of Praslin and west of Felicite Island. In size, it is the fourth-largest granitic island of Seychelles after Mahé, Praslin and Silhoue ...
, where they are a popular tourist attraction. Another isolated population of the species resides on the island of
Changuu, near
Zanzibar, and other captive populations exist in conservation parks in
Mauritius and
Rodrigues. The tortoises exploit many different kinds of habitat, including
grassland
A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge ( Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natu ...
s, low
scrub,
mangrove swamps
A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in several ...
, and coastal dunes.
Ecology
Habitat
A peculiar
habitat has
coevolved
In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...
due to the grazing pressures of the tortoises: "tortoise turf", a comingling of 20+ species of grasses and herbs. Many of these distinct plants are naturally dwarfed and grow their
seeds not from the tops of the plants, but closer to the ground to avoid the tortoises' close-cropping
jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...
s.
As the largest animal in its environment, the Aldabra tortoise performs a role similar to that of the
elephant
Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae a ...
. Their vigorous search for food fells trees and creates pathways used by other animals.
Feeding ecology
Primarily
herbivore
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...
s, Aldabra giant tortoises eat
grass
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...
es,
leaves
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
, woody plant stems, and fruit. They occasionally indulge in small invertebrates and
carrion
Carrion () is the decaying flesh of dead animals, including human flesh.
Overview
Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures, c ...
, even eating the bodies of other dead tortoises. In captivity, Aldabra giant tortoises are known to consume
fruits such as
apples and
banana
A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", distinguis ...
s, as well as compressed vegetable pellets. In 2020, a female Aldabra giant tortoise on
Fregate Island was observed hunting and eating a juvenile
lesser noddy
The lesser noddy (''Anous tenuirostris''), also known as the sooty noddy, is a seabird in the family Laridae. It is found near the coastlines of Comoros, Kenya, India, Maldives, Mauritius, Seychelles, Somalia, Sri Lanka and United Arab Emi ...
, indicating that the species was in the process of learning to catch birds.
Little fresh
water is available for drinking in the tortoises' natural habitat, so they obtain most of their moisture from their food.
The Aldabra giant tortoise has two main varieties of shells, related to their habitat. Specimens living in habitats with food available primarily on the ground have more dome-shaped shells with the front extending downward over the neck. Those living in an environment with food available higher above the ground have more flattened top shells with the front raised to allow the neck to extend upward freely.
Tortoise turf
The Aldabra giant tortoise is a herbivorous animal, spending much of its time browsing for food in its surrounding well-vegetated environment. The Aldabra giant tortoise is known to be found in places that are commonly known as "tortoise turf". Tortoise turf is composed of:
[Hnatiuk, R.J. and L.F.H. Merton (1979]
"Vegetation of Aldabra, a Reassessment"
''Atoll Research Bulletin'' No. 239, The Smithsonian Institution
Behavior
Aldabra tortoises are found both individually and in herds, which tend to gather mostly on open grasslands. They are most active in the mornings, when they spend time grazing and browsing for food. They dig wallows, hide under shade trees or in small caves, as well as submerge themselves in pools to keep cool during the heat of the day.
Lifespan
Large tortoises are among the longest-lived animals. Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers.
Adwaita
Adwaita (meaning "one and only" in Sanskrit) (c. 1750 – 22 March 2006), also spelled Addwaita, was a male Aldabra giant tortoise that lived in the Alipore Zoological Gardens of Kolkata, India. At the time of his death in 2006, Adwaita was be ...
was reputedly one of four brought by British seamen from the
Seychelles Islands
Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...
as gifts to
Robert Clive of the
British East India Company
The East India Company (EIC) was an English, and later British, joint-stock company founded in 1600 and dissolved in 1874. It was formed to trade in the Indian Ocean region, initially with the East Indies (the Indian subcontinent and Southea ...
in the 18th century, and came to
Calcutta Zoo
Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, commerci ...
in 1875. At his death in March 2006 at the Kolkata (formerly Calcutta) Zoo in India, Adwaita is reputed to have reached the longest ever measured
lifespan of 255 years (birth year 1750).
As of 2022,
Jonathan
Jonathan may refer to:
*Jonathan (name), a masculine given name
Media
* ''Jonathan'' (1970 film), a German film directed by Hans W. Geißendörfer
* ''Jonathan'' (2016 film), a German film directed by Piotr J. Lewandowski
* ''Jonathan'' (2018 ...
, a
Seychelles giant tortoise
The Seychelles giant tortoise (''Aldabrachelys gigantea hololissa''), also known as the Seychelles domed giant tortoise, is a tortoise subspecies in the genus ''Aldabrachelys''.
It inhabited the large central granitic Seychelles islands, but ...
, is thought to be the oldest living giant tortoise at the age of years, and Esmeralda, an Aldabra giant tortoise, is second at the age of years, since the death of
Harriet, a Galapagos giant tortoise, at 175. An Aldabra giant tortoise living on
Changuu off Zanzibar is reportedly years old.
Breeding
Between February and May, females lay between 9 and 25 rubbery fertilized
eggs
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
in a shallow, dry
nest
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materia ...
. Usually, less than half of the eggs are fertile. Females can produce multiple clutches of eggs in a year. After incubating for about eight months, the tiny, independent young hatch between October and December.
In captivity, oviposition dates vary.
Tulsa Zoo
The Tulsa Zoo is an non-profit zoo located in Tulsa, Oklahoma, United States. The Tulsa Zoo is owned by the City of Tulsa, but since 2010, has been privately managed by Tulsa Zoo Management, Inc. The zoo is located in Mohawk Park, one of the l ...
[Collins, Dave. (1984) "Captive Breeding and Management of the Aldabra Tortoise". Presented to 8th International Herpetological Symposium, Jacksonville Zoo, Jacksonville, Fl.] maintains a small herd of Aldabra tortoises and they have reproduced several times since 1999. One female typically lays eggs in November and again in January, providing the weather is warm enough to go outside for laying. The zoo also incubates their eggs artificially, keeping two separate incubators at 27 °C (81 °F) and 30 °C (86 °F). On average, the eggs kept at the latter temperature hatch in 107 days.
Conservation
The Aldabra giant tortoise has an unusually long history of organized conservation.
Albert Günther
Albert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther (3 October 1830 – 1 February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive re ...
of the British Museum, who later moved to the Natural History Museum of London (enlisting
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
and other famous scientists to help him) worked with the government of
Mauritius to establish a preserve at the end of the 19th century. The related, but distinct, species of giant tortoise from the Seychelles islands (Seychelles giant tortoise ''A. g. hololissa'' and Arnold's giant tortoise ''A. g. arnoldi'') are the subject of a captive-breeding and reintroduction program by the Nature Protection Trust of Seychelles.
[Swingland, Ian R. ''Aldabran Giant Tortoise.'' The Conservation Biology of Tortoises, Occasional Papers of the IUCN Species Survival Commission (SSC), No. 5, 1989.] A reference genome and low-coverage sequencing analyses has looked at revealing within- and among-island genetic differentiation within the Aldabra population, as well as assigning likely origins for zoo-housed individuals. This has managed to differentiate between individuals sampled on Malabar and Grande Terre and resolve the exact origin of zoo-housed individuals.
References
External links
Sea World Animal Bytes*
ttp://islandbiodiversity.com/tortoise.htm Seychelles Giant Tortoise Conservation Projectbr>
''Encyclopedia of Life''
{{Taxonbar , from=Q27885022
Aldabrachelys
Turtles of Africa
Fauna of Seychelles
Reptiles described in 1812
Articles containing video clips
Taxobox binomials not recognized by IUCN