Acanthoxyla inermis

Acanthoxyla inermis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Phasmatodea
Family: Phasmatidae
Genus: Acanthoxyla
Species: A. inermis
Binomial name
Acanthoxyla inermis
Salmon, 1955
Synonyms[1]

Acanthoxyla prasina Salmon, 1955

Acanthoxyla inermis[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] (the unarmed stick insect) is an insect which was described by John Tenison Salmon 1955. Acanthoxyla inermis is included in the genus Acanthoxyla, and family Phasmatidae.[20][21] No subspecies are listed.[20] The species is a netive of New Zealand but has since been unintentionally moved to Great Britain where it has grown a stable population and is the longest insect observed, and the most common of the stick insects which have established themselves on the island.[22]

Anatomy

Like many stick insects, A. inermis has a long thin body and three pairs of thin jointed limbs resembling the foliage it lives on. The species has been observed as having many superficial differences in appearance among individuals: The body colour and texture is varied and is thought to be related to the area the insect matures in, leading to members of the species being many shades green, brown or yellow. Adult members of this species can grow to 10 cm long.[23] The bodies of this genus are sometimes covered in spines while other specimens have perfectly smooth bodies and others still have a series of tubercles.[24]

Defense Mechanisms

Acanthoxyla inermis, like other stick insects is very well camouflaged for the environment it lives in. The long thin body is very hard to make out from real sticks which provides these insects with a way to hide in plain sight. As well as looking like a small branch in a tree, stick insects also behave like a part of the tree, performing swaying motions to give the appearance of moving in the breeze like the rest of the plant may.

Life Cycle

As members of the family Phasmidea, A. inermis grows by incomplete metamorphosis; it grows by a series of moults.[25] Generally a stick insect will moult between five and ten times between hatching from the egg and mature adulthood.[26] The life of a stick insect consists of four stages: Adults lay their ova (eggs) either by dropping them to the ground or depositing them within a suitable substrate. The ova are often hardy so they can withstand fall from height and the cold winter conditions they are often exposed to. The length of the egg stage can vary from as little as two weeks to over 18 months. After hatching from their eggs, nymphs quickly move to find a suitable piece to vegetation that they can scale in order to find food in the for of leaves and the safety of the environment they are so well camouflaged for. Nymphs go through a series of moults before maturing to an adults which allows them to grow win the absence of their hard exoskeleton and also regenerate limbs that may have been lost through a process called autotomy [27] Nymphs will generally eat their shed skin after a moult. Sub-adult stage refers to the final moult before being a true adult of its species. This is a short part of the life cycle and the last before the insect reaches the stage of reproduction[28]

The adult stage of a stick insect generally lasts six months to a year, during this period the animal's life is devoted to feeding and reproduction. A. inermis spends most of its life on trees, eating leaves in relative safety. A inermis seems to reproduce entirely asexually so while she feeds the female can fertilize and drop or deposit her own ova without having to move or compete with other members of her species for mates.

Reproduction

From what has been observed, A. inermis reproduces entirely asexually through a process called parthenogenesis. Given that they haven't been see to reproduce sexually at all they can be called obligately parthenogenic. Some other species of stick insect are facultatively parthenoginic meaning they can reproduce both sexually and asexually. The female of the species which appears to be the only members that are produced is able to spit her egg cells and recombine them to produce clones of herself,.[29] Because of the ability to carry on populations like this the male of the species is functionally redundant which has given A. inermis the ability to set up breeding populations from just one female individual. Such a situation occurred when timber was being transport to the United Kingdom in the 1920s[30] and since its arrival A. inermis has become the most common stick insect in Great Britain which has no native species of phasmatodea but several that have invaded in similar ways to the Unarmed Stick Insect. This form of reproduction does make A inermis (and others) vulnerable to environmental change as they have removed the mixing of their population's genetic code, reducing their genetic diversity,[31] as well as removing the chance for DNA repair.[32] It has also made species of stick insects which exist in the same habitat often difficult to identify; despite having been different species for a long time the process of parthenogenesis means that there has been a halt to adaptive morphological or physiological change.

Behavior

Stick insects are known for their behavioral adaptations for blending in with their environments. As well as their convincing appearance, stick insects are known to sway their bodies both when they walk and while stationary which has long been thought to make their camouflage more convincing; swaying like a twig in the wind. It has been suggested more recently that it may also help the animal's vision, helping it distinguish between those branches and leaves that move with it and objects unattached from the substrate it is on.[33]

In Maori culture

There is scattered mention of stick insects in Maori legends. Like all insects they are said to be children of Tane and are to be respected. They have been said to signify several different things: If a stick insect (or mantis) landed on a woman it was said to be a sign she was pregnant. It was said that if a stick insect is present the location was unsuitable for a garden. Other stories stated that if a stick insect landed on someone it was a sign they had entered a sacred place.[34]

References

  1. 1 2 Salmon (1991) , The stick insects of New Zealand, Reed Books, New Zealand, Auckland 1-124
  2. ↑ Otte & Brock (2005) , Phasmida Species File. Catalog of Stick and Leaf Insects of the world, The Insect Diversity Association at the Academy of Natural Sciences, Philadelphia 1-414
  3. ↑ Brock (2003) Rearing and Studying Stick and Leaf Insects. The Amateur Entomologist 22, Rearing and studying stick and leaf insects, The Amateur Entomologists' Society, London 22
  4. ↑ Seiler, C. & et al. (2000) , Phasmiden Pflege und Zucht von Gespenstschrecken, Stabschrecken und Wandelnden Blattern im Terrarium
  5. ↑ Trewick, Morgan-Richards & L.J. Collins (2008) Are you my mother? Phylogenetic analysis reveals orphan hybrid stick insect genus is part of a monophyletic New Zealand clade, Molecular Phylogenetics and Evolution 48(3):799-808
  6. ↑ Brock (1999) The amazing world of stick and leaf-insects, Amateur Entomologist, Amateur Entomologists Society (Amateur Entomologist) 26:1-165; 40 pp color plates
  7. ↑ Lee, M. (2006) The Stick-insects of Great Britain, Iteland and the Channel Isles, The Phasmid Study Group Newsletter (PSG Newsletter) 107:20-27
  8. ↑ Wise (1977) A Synonymic checklist of the Hexapoda of the New Zealand Sub-Region The Smaller Orders, Bulletin of the Auckland Institute and Museum 11:49-51 (Phasmatodea section)
  9. ↑ Jewell & Brock (2003[2002]) A review of New Zealand stick insects: new genera and synonymy, keys and a catalogue, Journal of Orthoptera Research (Jour. of Orthoptera Res.) 11(2):189-197
  10. ↑ Morgan-Richards & Trewick (2005) Hybrid origin of a parthenogenetic genus?, Molecular Ecology 14:2133-2142
  11. ↑ Trewick, Goldberg & Morgan-Richards (2005) Fewer species of Argosarchus and Clitarchus stick insects (Phasmida, Phasmatinae): evidence from nuclear and mitochondrial DNA sequence data, Zoologica Scripta 34(5):483-491
  12. ↑ Brock In Mazzini & Scali (1987[1986]) A third New Zealand stick insect (Phasmatodea) established in the British Isles, including a correction , Stick Insects: Phylogeny and reproduction. Proceedings of the 1st International Symposium on Stick Insects, Siena, University of Siena
  13. ↑ Salmon (1955) The genus Acanthoxyla (Phasmidae), Transactions of the Royal Society, New Zealand 82(5):1149-1156, pls. 44-47
  14. ↑ Palma, Lovis & Tither (1989) An annotated list of primary types of the phyla Arthropoda (except Crustacea) and Tardigrada held in the National Museum of New Zealand, National Museum of New Zealand Miscellaneous Series No. 20:1-49
  15. ↑ Lee, M. (2009) A 2009 update on the UK's Naturalised Stick-insects, The Phasmid Study Group Newsletter (PSG Newsletter) 119(15-20)
  16. ↑ Lee, M. (1998) An updated survey of the distribution of the stick insects of Britain, Phasmid Studies 7(1):18-25
  17. ↑ Lee, M. (1995) A survey into the distribution of the stick insects of Britain, Phasmid Studies 4(1):15-23
  18. ↑ Brock (2009) The Unarmed Stick-insect Acanthoxyla inermis in Hampshire, The Phasmid Study Group Newsletter (PSG Newsletter) 119(2, 11)
  19. ↑ Haes (2002) A menu of phasmid fodder, Bulletin of the Amateur Entomologist’s Society 61(441):45-47
  20. 1 2 Bisby, F.A.; Roskov, Y.R.; Orrell, T.M.; Nicolson, D.; Paglinawan, L.E.; Bailly, N.; Kirk, P.M.; Bourgoin, T.; Baillargeon, G.; Ouvrard, D. (2011). "Species 2000 & ITIS Catalogue of Life: 2011 Annual Checklist.". Species 2000: Reading, UK. Retrieved 24 September 2012.
  21. ↑ PhasmidaSF: Phasmida Species File . Brock P., 2010-04-14
  22. ↑ Chapman, D. saga.co.uk
  23. ↑ Chudleigh, b "Stick insects">http://www.nzgeographic.co.nz/archives/issue-83/stick-insects
  24. ↑ http://animals.nationalgeographic.com/animals/bugs/stick-insect/
  25. ↑ http://wwx.inhs.illinois.edu/resources/inhsreports/jul-aug98/stick/ "Illinois Natural History Survey"
  26. ↑ http://www.keepinginsects.com/stick-insect/faq/
  27. ↑ "Archived copy". Archived from the original on 2015-12-29. Retrieved 2015-03-26.
  28. ↑ http://www.keepinginsects.com/stick-insect/general/
  29. ↑ http://www.biology.ualberta.ca/locke.hp/walk_sticks.htm
  30. ↑ http://www.saga.co.uk/lifestyle/gardening/wildlife-watch/stick-insect.aspx
  31. ↑ http://occupytheory.org/advantages-and-disadvantages-of-asexual-reproduction/
  32. ↑ http://www.darwinwasright.org/recombination.html
  33. ↑ Steve Trewick. 'Stick insects - Forest phantoms', Te Ara - the Encyclopedia of New Zealand, updated 13-Jul-12 URL: http://www.TeAra.govt.nz/en/stick-insects/page-1
  34. ↑ (http://www.teara.govt.nz/en/stick-insects/page-1)
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