Astrochelys yniphora

Geographic Range

Ploughshare tortoises are endemic to the Baly Bay area of northwestern Madagascar. There are five isolated populations within thirty kilometers of Baly Bay that consist of less than 600 total individuals in the wild. The five populations include Cape Sada (150 hectares), Ankasakabe (50 hectares), Beheta (200 hectares), Betainalika (340 hectares), and Ambatomainty-Andranolava (500 hectares). Each population is separated by a geographical barrier such as the Andranomavo River, which isolates the west and the east populations. The total world range of ploughshare tortoises lies within an area of only about one hundred square miles.

• Biogeographic Regions
• ethiopian ethiopian
  • native native

• Other Geographic Terms
• island endemic island endemic

Habitat

Ploughshare tortoises are terrestrial and live in bamboo scrub ( Perrierbambos madagascariensis ) savannahs with palms ( Bismarckia nobilis ) and shrub thickets ( Terminalia boivinii ) in a hot-tropical, semi-humid zone. This xeric scrub forest includes the plant species Chadsia grevei , Alloteropsis semialata , Clerodendron incisum , Casaythra species, Heteropogon contortus , and Bismarckia nobilis . Ploughshare tortoises find protection in dense thickets but prefer to forage in open grassy areas.

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• scrub forest scrub forest

Physical Description

The heads and snouts of ploughshare tortoises range in color from black to various shades of brown with yellow spots near the ear. As with all tortoises, they lack teeth, but their beaked jaw is extremely powerful. The neck, limbs, and tail are usually brown with some tan or yellow. They have flattened legs with scaly, armored skin and clawed toes on each foot. Ploughshare tortoises have a distinctly large gular scute, which curves up towards the neck. This creates a plough-shaped projection between the front legs, hence the name ploughshare. The oval, high-domed carapace usually has eleven marginals on each side with an additional larger one on the posterior. Each marginal is yellowish-brown darkening towards the edges with thin, black hexagonal growth rings on each scute. The plastron is yellow with some brownish tint. With age, the carapace becomes darker in color and more monotone (A. Mandimbihasina, pers. comm.).

Male, adult ploughshare tortoises have a weight that ranges from 7.2 to 18.9 kilograms (mean 10.3 kilograms). Adult females weigh from 5.5 to 12 kilograms (mean 8.8 kilograms). Males are larger than females, possessing a longer gular scute as well as longer, thicker tails. The length of ploughshare tortoises also varies between males and females. Adult females range from 30.7 to 42.6 centimeters long (mean 37 cm). Adult males range from 36.1 to 48.6 centimeters (mean 41.5 cm). Another way to differentiate between sexes is by flipping the tortoise over and looking at the plastron, anal notches, and anal forks. Females have a flat plastron, while males have concave plastrons. Additionally, males have longer anal forks, and females have larger anal notches that are big enough for the eggs they produce (A. Mandimbihasina, pers. comm.).

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes shaped differently

Development

Ploughshare tortoises are amniotes. They progress through vertebrate embryonic development to hatching. Adults grow about 5% per year, while juveniles grow 15% each year. Sexual maturity is reached at about 20 years. Growth is slowed at that point but does not come to a halt.

The sex of ploughshare tortoises is determined by incubation temperature. However, temperature ranges that determine sex are not known. Additionally, all eggs in a particular hole are the same sex. Sex cannot be determined until tortoises reach sexual maturity around 20 years of age (A. Mandimbihasina, pers. comm.).

• Development - Life Cycle
• temperature sex determination
• indeterminate growth indeterminate growth

Reproduction

Ploughshare tortoises mate from October to February, mostly in the months of November and December. Courtship begins with the male sniffing and then circling the female five to thirty times. The male pushes the female, sometimes biting at the female’s head and forelimbs. When mating, the male’s enlarged epiplastron penetrates under the female’s carapace. The male uses his gular scute as leverage to overturn the female. The female lifts her hind legs in order to hoist the posterior shell. Only the male vocalizes, projecting single, continuous calls. Both males and females have multiple mates, however there are many days between each partner (A. Mandimbihasina, pers. comm.).

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Nesting occurs three months after mating in open areas within grasslands, bamboo stands, burnt areas, or savannah. Nesting is usually near a bush, log, or tree and usually takes place in the late morning. The female digs a shallow pit with her hind legs and urinates to moisten the soil during excavation. The average hole width is 11.43 centimeters and 10.92 centimeters deep. She packs the soil tightly over the eggs and then abandons them. Female ploughshare tortoises may lay four to five clutches, each one month apart. The clutch size can range from 1 to 6 (mean 3.2) spherical white eggs that have a diameter of about 4.19 to 4.7 centimeters and mean egg weight of 36.2 grams (range 20 to 54 grams).

The incubation period ranges from 197 to 281 days, with an average of 237 days. Rainfall in the beginning of November usually leads to hatching. Young emerge during the daytime and typically have a carapace length of 42 to 46 millimeters. They are completely independent upon hatching.

In a study of two populations for five years, ploughshare tortoises had an egg fertility rate of 71.9 percent and a hatching success rate of 54.6 percent. Each year, a female averages 4.3 hatchlings.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

Ploughshare tortoises are completely independent upon hatching. Females invest significant energy in supplying eggs with nutrients and laying clutches in protected places.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Although ploughshare tortoises live a long time, the actual lifespan is unknown. It is estimated that ploughshare tortoises live between 50 and 100 years. The lifespan is longer in zoos due to veterinary care, adequate nutrition, and lack of predators. Ploughshare tortoises reach sexual maturity around twenty years of age. Growth rings can be used to measure how old a tortoise is. However, the carapace becomes smooth when the tortoise reaches about thirty years old, making growth rings hard to count (A. Mandimbihasina, pers. comm; D. Uyeda, pers. comm.).

Adult ploughshare tortoises have an annual survival rate of 97%. Juvenile tortoises have an annual survival rate of 44 to 96%, which is determined by their size. Usually, the larger the individual, the higher the annual survival rate.

Behavior

Ploughshare tortoises are diurnal. They are usually inactive from May through October, during the cool, dry season. They are most active during the rainy months of November and December; this includes courtship, mating, and hatching. They forage in the morning and late afternoon. Instead of digging burrows, like many other tortoises, ploughshare tortoises use surface litter as protection.

Mature males must engage in a wrestling match in competition for access to females. During this contest, each male attempts to overturn its opponent using its gular scute. The winner then searches for a female mate.

• Key Behaviors
• terricolous
• diurnal diurnal
• motile motile
• sedentary sedentary
• hibernation hibernation
• solitary solitary

Home Range

Sex, season, and age affect the size of home ranges in ploughshare tortoises. Females have smaller home ranges than males, and home ranges are smaller in the dry season than the rainy season. Females average about 4 hectares in the dry season compared to 13 hectares in the rainy season. Males have a larger home range of 7 hectares in the dry season and 21 hectares in the rainy season. Adults have a larger home range than juveniles, which travel only 0.1 to 0.3 hectares.

Ploughshare tortoises have a low density of about 0.55 to 0.71 per hectare. The wild male to female ratio is equal, at 1:1. Due to low populations at Cape Sada, the male to female ratio is 1:2.

Communication and Perception

The only communication known is that males vocalize during mating by projecting singular continuous calls. So far, no further study has been done on the vocalizations of ploughshare tortoises. Like other tortoises, ploughshare tortoises likely use vision and smell extensively in their foraging and navigation (A. Mandimbihasina, pers. comm.).

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical

Food Habits

Ploughshare tortoises are largely herbivorous. Their diet consists of many types of fruits, leaves, and the feces of some animals including lemurs ( Lemuriformes ) and introduced bushpigs ( Potamochoerus larvatus ). They eat the leaves of shrubs but rarely eat bamboo leaves, which can contain high levels of cyanide. They forage on the grass Heteropogon contortus , but favor the shrub Bauhinia pervillei (A. Mandimbihasina, pers. comm.).

At the Honolulu zoo, a female ploughshare tortoise is fed on alternate days with browse and a mixed diet. Browse includes sweet potato vines, flowers and leaves of hibiscus, dandelion, Opuntia , or hau. The mixed diet consists of ground carrots and celery as well as cut up orange, apple, and banana. This mixed diet also includes horse pellets, made of bionate and calcium (D. Uyeda, pers. comm.).

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • frugivore frugivore
• coprophage coprophage

• Plant Foods
• leaves
• fruit

• Other Foods
• dung

Predation

One predator of ploughshare tortoises is the introduced African bushpig ( Potamochoerus larvatus ), which kills eggs and juveniles. There is a large population of Potamochoerus larvatus because local Muslims seldom hunt them. Rarely, snakes and birds prey on eggs and young tortoises. Humans are predators because many tortoises are hunted for the illegal pet trade or to eat. Although there are laws prohibiting it, there is still smuggling going on today. Additionally, humans are responsible for bush fires, which result in habitat destruction. Since ploughshare tortoises take a long time to mature sexually and reproduce, populations take a long time to recover even if predation is controlled. Ploughshare tortoises have a population growth rate of only 1% each year (A. Mandimbihasina, pers. comm.).

Ecosystem Roles

Amblyoma geochelone is a recently discovered species of tick that is a host-specific ectoparasite of ploughshare tortoises. Given its host-specificity, it is thought that A. geochelone may also be endangered. This parasite does not seem to substantially harm ploughshare tortoises. Ploughshare tortoises may be important in dispersing the seeds of the fruits they eat.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

Ploughshare Tortoises are consumed by humans. In the past, sailors ate the tortoises as a source of fresh meat. Additionally, Arab traders exported ploughshare tortoises as food to the nearby Comoro Islands. Although this ended in the nineteenth century, many people still eat the tortoises; this does not include the local Malagasy people (A. Mandimbihasina, pers. comm.).

Although trade in ploughshare tortoises is illegal by international convention, there is a black-market in captive tortoises. In January 2008, a Nigerian man was arrested with three different passports each from different countries with a separate identity. He had 300 tortoises, 8 of which were ploughshare tortoises. He could have sold them in the exotic pet trade market making as much as $200,000. Additionally, 3 more ploughshare tortoises were confiscated in Bangkok in April 2008. More recently, in February 2009, two were confiscated from a man in Hong Kong. Juveniles sell for at least $1,000, while adults can sell for up to $30,000 each in Bangkok, Thailand.

• Positive Impacts
• pet trade pet trade
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

There are no known negative impacts of ploughshare tortoises on humans.

Conservation Status

The IUCN Red List 2008 classifies Astrochelys yniphora as critically endangered. This species is also listed on Appendix I of CITES, and Malagasy law prohibits hunting and collecting of ploughshare tortoises.

Ploughshare tortoise are the world’s rarest tortoises and are being bred in captivity for release into the wild. The Forestry Station at Ampijoroa, located only 150 kilometers from Baly Bay, is the main captive breeding center of ploughshare tortoises. They did not take any tortoises from the wild. Instead, they obtain tortoises from Malagasy authorities who confiscate them from illegal captivity. Besides one hatching at the Honolulu Zoo, ploughshare tortoises had never before bred successfully in captivity. Starting in 1986 with only eight tortoises, the Forestry Station had successfully raised sixty-two young by 1992. Hatch and survival rates increase each year with increased research and techniques on health, diet, breeding, and hatching. Currently, there are seventeen adults, which consist of seven females and ten males, as well as over two hundred offspring. This is enough juveniles to start a release program. Over a four year period, twenty tortoises will be released each year to the same location in the wild (A. Mandimbihasina, pers. comm.).

Other Comments

Astrochelys yniphora is also known by the common names: angonoka (Malagasy), angulated tortoises, plowshare tortoises, and Madagascan tortoises.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web, James Harding (editor), Michigan State University.

Lisa Fishbeck (author), Michigan State University, Pamela Rasmussen (editor, instructor), Michigan State University.

References

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