Hemideina thoracica | |
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Scientific classification
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Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Orthoptera |
Suborder: | Ensifera |
Family: | Anostostomatidae |
Genus: | Hemideina |
Species: | H. thoracica
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Binomial name | |
Hemideina thoracica (White, 1846)
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Synonyms | |
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Hemideina thoracica, commonly known as the Auckland tree wētā or tokoriro [1] [2] is a cricket-like insect (within the family Anostostomatidae). [2] [3] It is endemic to New Zealand and is found over most of the North Island, except for the Wellington region and regions 900 metres above sea level. [4] [5] [6] This species is an arboreal, herbivorous [7] [8] [9] generalist however, it is also thought to be polyphagous [10] and is found in all wooded habitats, including forest, scrub and suburban gardens. [6] [11] [12]
H. thoracica is morphologically uniform but chromosomally polymorphic. [13] [14] It comprises at least eight chromosomal races with diploid numbers from 2n=11 (XO) to 2n=23 (XO). There are hybrid zones where some of the chromosomal races meet. [14] Phylogenetically, it is most closely related to the other North Island species ( H. crassidens and H. trewicki). [15] The conservation status of H. thoracica is " not threatened" [16] [17] however, the chromosome race on Karikari Peninsular (2n=23/24) is listed as " nationally vulnerable". [17]
Hemideina thoracica was first described by Scottish zoologist Adam White in 1846, but at that time included in the genus Deinacrida. [18] It was later made the type species for the wētā genus Hemideina, described in 1869 by Walker. [18]
The Auckland tree wētā, Hemideina thoracica is endemic to New Zealand and has a wide distribution over the northern two-thirds of the North Island. [5] It is abundant in central and north North Island where it inhabits forest or scrub at lowland elevation. [19] As a nocturnal and arboreal herbivore [19] this species uses tree cavities to rest and conceal itself in during the day before emerging at night to feed. [8] [2] [5] [6] It is parapatric with two other Hemideina spp. in the North Island: H. crassidens and H. trewicki [5] and in warmer areas it is thought to competitively exclude H. crassidens which is distributed in the lower North Island and north-west of the South Island. [5] [6]
Like other tree wētā Hemideina thoracica forages arboreally [9] at night, eating mostly leaves and some fruit and seeds from a range of different plants. [12] [7] Recently, it has been suggested that this species feeds selectively on a range of plant species and is omnivorous with invertebrates and fruit and seeds included in the diet. [10] Plants are selectively eaten with species such as Mahoe (Melicytus ramiflorus) or Karamu (Coprosma robusta) preferred. [2] [7] [9] However, Auckland tree wētā also feed on small insects [9] [2] and are thought to be polyphagous. [10] H. thoracica inhabiting higher elevation sites have been shown to consume more invertebrates and fewer plant species than those at low elevation habitats. [10]
Hemideina thoracica are large-bodied as adults (3–7 g), being up to 40mm in length. [2] [7] The abdomen is brown and the pronotum pale with dark hieroglyph-like markings. [6] This body colouration makes H. thoracica easily distinguishable from the Wellington tree wētā (H. crassidens) with which it is parapatric. [6] As in other Hemideina spp. spines are present on the hind legs which function in defense. [2] [11] Morphometric analysis of spination patterns has shown that both H. thoracica and H. crassidens lack the mid-tibial ‘1/3 back’ spine which differentiates these species from all other Hemideina spp.. [11] Hemideina thoracica has the thinnest femur and tibia compared with all other New Zealand tree wētā (Hemideina spp). [11] Adults are sexually dimorphic with males having enlarged mandibles used for fighting other males. [20] [21]
Hemideina thoracica is chromosomally polymorphic meaning that differential chromosomal arrangement occurs among populations of this species. [14] [13] Nine distinct chromosome races each comprising a different karyotype have been described and these range in diploid numbers from 2n=11 (XO) to 2n=23 (XO). [14] [13] Five different hybrid zones have been located where, in different combinations six of the nine chromosome races come into contact with one another. [14] Three of these zones ( Mt. Camel, Karikari and Waitangi) involve northern chromosome races which likely originated in the Pliocene, whereas the southern races in the Bream Bay and Taupō zones are likely to be much younger. [14] [22] Despite having differing chromosome numbers, morphology of H. thoracica is uniform [13] [14] (see 'Morphology' above).
Hemideina thoracica is capable of producing sound using stridulation of the metathoracic legs and the abdomen. [23] Both males and females produce a rasping sound when disturbed by raising and extending the legs above the body followed by a defensive kick while tightly holding the legs against the abdomen. [23] Using abdominal oscillation, males also generate an intraspecific song when in close contact with one another. [23] However, H. thoracica has poor mate recognition systems and forms sterile hybrids with H. crassidens and H. trewicki where they are sympatric in the southern North Island. [24]
As a nocturnal species, H. thoracica occupy cavities during the day [2] [5] [6] [8] and occupancy patterns have been shown to be influenced by both season and sex of previous occupants. [20] Females tend to avoid cavities in which other females reside and are found in cavities alone however, this changes during summer when females form harems [20] Males and females which were previously living apart begin living together in early summer. [20]
It has been suggested that Auckland tree wētā have a polygynandrous mating system whereby both males and females mate with multiple partners. [20] This species is a hemimetabolous insect whose eggs hatch in Spring with a minimum of eight instars required to reach adulthood. [20] Females lay eggs in the soil and provide no maternal care.
The conservation status of Hemideina thoracica is " not threatened" [16] [17] however, the chromosome race on Karikari Peninsular (2n=23/24) is listed as " nationally vulnerable". [17] Artificial refuges have been used to monitor populations of H. thoracica and H. crassidens [25] and could potentially be used in conservation management of these species by providing available habitat. [8] [25]
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