Dryococelus australis, commonly known as the Lord Howe Island stick insect or tree lobster, is a species of stick insect which lives on the Lord Howe Island Group. It was thought to be extinct by 1920, only to be rediscovered in 2001. It is extinct in its largest habitat, Lord Howe Island, and has been called "the rarest insect in the world", as the rediscovered population consisted of 24 individuals living on the small islet of Ball's Pyramid.
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Anatomy and behaviour
Adult Lord Howe Island stick insects can measure up to 15 centimetres (6 in) in length and weigh 25 grams (1 oz), with males 25% smaller than females. They are oblong in shape and have sturdy legs. Males have thicker thighs than females. Unlike most phasmida, the insects have no wings, but are able to run quickly.
The behaviour of this stick insect is highly unusual for an insect species, in that the males and females form a bond.
The females lay eggs while hanging from branches. Hatching can happen up to nine months later. The nymphs are first bright green and active during the day, but as they mature, they turn black and become nocturnal.
Reproduction can happen without the presence of males (parthenogenesis) and this facility has allowed the species to survive when they are low in numbers.
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History and conservation
The stick insects were once very common on Lord Howe Island, where they were used as bait in fishing. They were believed to have become extinct soon after the supply ship SS Makambo ran aground on the island in 1918, allowing black rats to become established. After 1920, no stick insects could be found. However, in 1964, a team of climbers visiting Ball's Pyramid, a rocky sea stack 23 kilometres (14 mi) south-east of Lord Howe Island, discovered a dead Lord Howe Island stick insect. During subsequent years, a few more recently-dead insects were discovered by climbers, but expeditions to find live specimens were unsuccessful.
In 2001, Australian scientists David Priddel and Nicholas Carlile hypothesized that there was sufficient vegetation on the islet to support a population of the insects, and with two assistants travelled there to investigate further. They scaled 120 m of grassy, low-angled slope, but only found crickets. On their descent, the team discovered large insect droppings under a single Melaleuca shrub growing in a crevice approximately 100m above the shoreline. They deduced that they would need to return after dark, when the insects are active, to have the best chance of finding living specimens. Carlile returned with local ranger Dean Hiscox and, with a camera and flashlights, scrambled back up the slopes. They discovered a small population of 24 insects living beneath the Melaleuca shrub amongst a substantial build-up of plant debris.
In 2003, a research team from New South Wales National Parks and Wildlife Service returned to Ball's Pyramid and collected two breeding pairs, one destined for a private breeder in Sydney and the other sent to the Melbourne Zoo. After initial difficulties, the insects were successfully bred in captivity in Melbourne. The ultimate goal was to produce a large population for reintroduction to Lord Howe Island, providing that a project to eradicate the invasive rats was successful. In 2006, the captive population of insects numbered about 50 individuals, with thousands of eggs still to hatch. In 2008, when Jane Goodall visited the zoo, the population had grown to 11,376 eggs and 700 individuals, 20 of which were soon after returned to a special habitat on Lord Howe Island. As of April 2012, the Melbourne Zoo had reportedly bred over 9,000 of the insects, including 1,000 adult insects, plus 20,000 eggs.
In 2014 an unauthorised climbing team sighted live stick insects near the summit of Balls Pyramid, in a thicket of sedge plants rooted in very thin soils at an altitude of 500 metres, suggesting that the insect's range on the Pyramid is more widespread than previously thought, and that its food preferences are not limited to Melaleuca howeana.
By the beginning of 2016, Melbourne Zoo had hatched 13,000 eggs, and had also sent eggs to the Bristol Zoo in England, the San Diego Zoo in the United States, and the Toronto Zoo in Canada, to establish distinct insurance populations.
A 2017 study comparing DNA sequences of phasmids originating from Ball's Pyramid with those from museum specimens from Lord Howe Island showed that the Ball's Pyramid sequences differ from those of Lord Howe Island by a degree comparable to variation within the museum specimens, despite some morphological differences between the two groups. This confirms that the two populations represent the same species. The genome was found to be very large in size (over 4 Gb) and is probably hexaploid.
Source of the article : Wikipedia
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