Stokes's skink

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Stokes's skink
2009-03-07Egernia stokesii059.jpg
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Family: Scincidae
Genus: Egernia
Species:
E. stokesii
Binomial name
Egernia stokesii
(Gray, 1845)
Distribution Map of Egernia Stokesii.jpg
Distribution Map of Stokes's skink
Synonyms [2]
  • Silubosaurus stokesii
    Gray, 1845
  • Silubosaurus zellingi
    De Vis, 1884
  • Egernia stokesii
    Glauert, 1960

Egernia stokesii is a gregarious species of lizard of the Scincidae family. [3] This diurnal species is endemic to Australia, and is also known as the Gidgee skink, spiny-tailed skink, Stokes's skink and Stokes's egernia. [4] The species forms stable, long-term social aggregations, much like the social groups seen in mammalian and avian species. [5] This characteristic is rarely found in the Squamata order, but is widespread within the Australian subfamily of Egerniinae skinks. [4] [6] Populations of E. stokesii are widely distributed, but fragmented, and occur in semi-arid environments. [7] There are three recognised subspecies. [8] The conservation status for the species is listed as least concern, however, one subspecies is listed as endangered. [1] [8]

Contents

Description and ecology

Stokes's skink basking on a rock, displaying scatterings of lighter coloured dorsal scales. Egernia stokesii on rock.jpg
Stokes's skink basking on a rock, displaying scatterings of lighter coloured dorsal scales.

Egernia stokesii range in colour from olive to reddish brown, with lighter ventral scales that range from white to yellow. [3] The species often displays scatterings of lighter coloured dorsal scales. [3] The dorsal scales are keeled from the back of the neck to the tail [7] [3] and spiny tail scales are a prominent feature of the species. [4] The tail is flattened rather than cylindrical, and shorter than the head and body of the animal, at approximately 35% of the snout to vent length. [3] E. stokesii is unable to autotomize their tails. [4] The snout to vent length of a mature adult is between 155 and 190mm. [4] The species is slow to reach sexual maturity, generally between five and six years of age, with a lifespan between 10 and 25 years. [5] [4]

The characteristic spiny tail of Stokes's skink. E stokesii.jpg
The characteristic spiny tail of Stokes's skink.

The species displays complex social organisation, forming social aggregations of up to 17 closely related individuals. [5] [4] It has been suggested complex social organisation in the species aids in the detection of predators and thermoregulation. [4] These aggregations remain stable over time, with evidence of adult individuals remaining in the same social group for over five years. [4] E. stokesii displays philopatry, [9] with juveniles typically remaining within the natal group until maturity. [4] The social aggregations typically consist of a breeding pair, immature juvenile and sub-adult offspring from successive litters, and other closely related individuals. [4] Each group has a defined home range, with several core, preferred rock or log crevices shared by group members within the home range. [5] [10] Each group shares a common scat pile outside these refuge crevices, and are able to distinguish group members from non-group members using olfactory chemical cues. [4] [10] [5] Multiple groups may share the crevices on the margins of home ranges. [5] The individuals within these social groups bask in close contact with one another, at times touching, and the basking sites are adjacent to crevices. [5]

The species is omnivorous, with the diet including arthropods such as beetles and grasshoppers, and plant material. [11] The seeds of both native and introduced flora species have been found in scats, such as the native Enchylaena tomentosa (ruby saltbush), and the introduced Portulaca oleracea (common pig weed) and Medicago minima (woolly burr medic). [11] Both seasonal and ontogenetic dietary changes have been reported in the species, with the juvenile diet consisting of a higher proportion of insects to plant matter. [11] Adults consume a proportionally higher percentage of plants to insects, and this plant portion increases during mid to late summer. [11] The reason for these dietary changes has not been established, although it is possible competitive pressure from juveniles following parturition, or seasonal changes in resource availability may contribute. [11]

Potential predators include mammals such as cats, foxes and dingos. [7] Reptiles such as the eastern brown snake [4] and monitors, as well as birds of prey may also prey upon the species. [7] The species uses two key mechanisms to reduce predation; the spiny tail morphology and defensive behaviours such as seldom straying far from rock crevice refuges. [4]

A close up of the head of Stokes's skink. E stokesii 2.jpg
A close up of the head of Stokes's skink.
Stokes's skink sheltering in a rock crevice. Egernia stokesii in crevice.jpg
Stokes's skink sheltering in a rock crevice.
Stokes's skink. Egernia stokesii Basking.jpg
Stokes's skink.

Habitat and distribution

E. stokesii may be saxicolous, occupying rocky outcrops, or semi-arboreal, and found in grassland, woodland or shrubland habitats. [4] [1] They are diurnal and non-burrowing, instead sheltering in rock crevices, under logs, or in tree hollows. [4] E. stokesii is found in New South Wales, Northern Territory, Queensland, South Australia, and Western Australia. [2]

Reproduction

The species is highly monogamous, [7] and there is evidence of mate selection favouring unrelated individuals with dissimilar genotypes and high genetic diversity, from within the established social group. [9] E. stokesii are viviparous, producing between 1 and 8 young each litter. [5] The parturition timeframe varies between one and twelve days, with an average time of 2.8 days. [12] The size of the litter has been demonstrated to positively correlate with both the snout to vent length and gravid mass of the female. [12] The young are presented head first, and encased in membranes with a yolk sac attached. [5] The newborn skinks or mother may consume the birth membranes and yolks sac following parturition, and infanticide has been observed in the species. [4] [12] The reported snout to vent length of newborn juveniles is between 65-95mm, [5] with an average birth weight of 8.15g. [12] Populations of E. stokesii in eastern Australia typically give birth annually between during the summer months of February and March, but may not produce a litter every year. [12] [7] [5] A winter birth has been observed in a wild individual from Western Australia. [7] Juveniles experience a relatively higher infant mortality rate in their first year, whilst adults have a low mortality rate. [4]

Evolutionary relationships

Egernia stokesii, along with all Australian skinks, are grouped within the Scincidae Lygosominae subfamily. [6] There are three monophyletic radiations of Australian skinks within this subfamily: Sphenomorphinae, Eugonylinae and Egerniinae, with E. stokesii grouped in the Egerniinae subfamily, previously known as the Egernia group. [6] The Egerniinae includes 8 genera, including Egernia, Tiliqua and Cyclodomorphus, with 61 extant species distributed across Australia, New Guinea and the Solomon Islands. [6] Molecular systematics has resulted in the partitioning of the previous Egernia genus into four distinct genera: Lissolepis (Peters, 1872), Liopholis (Fitzinger, 1843), Bellatorias (Wells and Wellington, 1943), and Egernia (Gray, 1838) [13] [6] . The genus Corucia , endemic to the Solomon Islands, is considered the sister group to Australian Egerniinae. [6]

Morphological and molecular data analysed using Bayesian phylogenetic analysis suggests the Egerniinae began to radiate in mainland Australia approximately 35 million years ago, sometime between the late Eocene and early Oligocene epochs, [6] likely as a result of climatic fluctuations between glacial and desertification periods. [4] Of the Egerniinae, the evidence suggests the subclade Lissolepis as basal, and the earliest-branching. [6] Depending on the method of phylogenetic analysis, the Egernia genus has been identified as a sister group to the Tiliqua and Cyclodomorphus clade, or as a paraphyletic grouping with Tiliqua and Cyclodomorphus [6] . It is suggested these three genera begun to diverge over 30 million years ago, during the Oligocene epoch. [6]

Etymology

The specific name, stokesii, is in honour of Royal Navy Admiral John Lort Stokes. [14]

The subspecific name, zellingi, is in honour of British biological collector Charles Weldon De Burgh Birch, Count Zelling (1821–1894). [15] [16]

Subspecies

There are three currently recognised subspecies of Egernia stokesii, each with distinct geographic distributions: E. stokesii badia, E. stokesii stokesii and E. stokesii zellingi [8] . E. stokesii zellingi is found in semi-arid areas of South Australia, New South Wales, the Northern Territory and Queensland. [8] [7] E. stokesii stokesii occurs on the islands of Abrolhos Archipelago, off the coast of Western Australia. [8] E. stokesii badia is found in the Wheatbelt, Murchison and Shark Bay areas of Western Australia. [8] E. stokesii badia also includes the former subspecies E. stokesii aethipos, which occurs as an isolated population on Baudin Island, Shark Bay. [8]

Conservation status

Egernia stokesii is categorised by the International Union for the Conservation of Nature Red List as Least Concern. [1] However, the current population has been assessed as decreasing; affected by severely fragmented populations and processes that alter or degrade habitats, such as agricultural activities, mining and altered fire regimes. [1]

The subspecies E. stokesii badia, commonly known as the Western spiny-tailed skink, is listed as endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999. [8] The key threats to the species include land clearing, grazing and cropping. [8]

Related Research Articles

<span class="mw-page-title-main">Skink</span> Family of reptiles

Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Skinks are characterized by their smaller legs in comparison to typical lizards and are found in different habitats except arctic and subarctic regions.

<i>Egernia</i> Genus of lizards

Egernia is a genus of skinks that occurs in Australia. These skinks are ecologically diverse omnivores that inhabit a wide range of habitats. However, in the loose delimitation the genus is not monophyletic but an evolutionary grade, as has long been suspected due to its lack of characteristic apomorphies.

<span class="mw-page-title-main">Pink-tongued skink</span> Species of lizard

The pink-tongued skink is a species of lizard in the family Scincidae. C. gerrardii is endemic to Australia, where it is also called commonly the pink-tongued lizard. As suggested by these common names, its distinguishing characteristic is a pink tongue as opposed to the blue tongue of lizards of the closely related genus Tiliqua.

<span class="mw-page-title-main">Blue-tongued skink</span> Genus of lizards

Blue-tongued skinks comprise the Australasian genus Tiliqua, which contains some of the largest members of the skink family (Scincidae). They are commonly called blue-tongued lizards or simply blue-tongues or blueys in Australia or panana in Indonesia. As suggested by these common names, a prominent characteristic of the genus is a large blue tongue that can be bared as bluff-warning to potential enemies. The type of predator/threat that is near will determine the intensity of colour present in the tongue. The tongue can also deform itself and produce a thick mucus in order to catch prey. They are relatively shy in comparison with other lizards, and also significantly slower due to their shorter legs.

<span class="mw-page-title-main">Threatened fauna of Australia</span> Animals at risk of becoming extinct

Threatened fauna of Australia are those species and subspecies of birds, fish, frogs, insects, mammals, molluscs, crustaceans and reptiles to be found in Australia that are in danger of becoming extinct. This list is the list proclaimed under the Australian federal Environment Protection and Biodiversity Conservation Act 1999. The classifications are based on those used by the World Conservation Union (IUCN), however IUCN and Australian rankings do differ. Each state and territory has its own legislation relating to environmental protection.

<i>Tiliqua rugosa</i> Species of lizard

Tiliqua rugosa, most commonly known as the shingleback skink or bobtail lizard, is a short-tailed, slow-moving species of blue-tongued skink endemic to Australia. It is commonly known as the shingleback or sleepy lizard. Three of its four recognised subspecies are found in Western Australia, where the bobtail name is most frequently used. The fourth subspecies, T. rugosa asper, is the only one native to eastern Australia, where it goes by the common name of the eastern shingleback.

<span class="mw-page-title-main">Cunningham's spiny-tailed skink</span> Species of lizard

Cunningham's spiny-tailed skink, also known commonly as Cunningham's skink, is a species of large skink, a lizard in the family Scincidae. The species is native to southeastern Australia.

<span class="mw-page-title-main">King's skink</span> Species of lizard

King's skink is a species of skink, a lizard in the family Scincidae. The species is endemic to Australia.

The great desert skink, also known as Kintore's egernia and by various names including tjakura in various Aboriginal Australian languages, is a species of skink, a lizard in the family Scincidae. The species is endemic to the western half of Australia. It is a burrowing lizard and extremely social.

<span class="mw-page-title-main">Lygosominae</span> Subfamily of lizards

Lygosominae is the largest subfamily of skinks in the family Scincidae. The subfamily can be divided into a number of genus groups. If the rarely used taxonomic rank of infrafamily is employed, the genus groups would be designated as such, but such a move would require a formal description according to the ICZN standards.

<span class="mw-page-title-main">White's skink</span> Species of lizard

White's skink, also known commonly as White's rock skink, is a species of lizard in the family Scincidae. The species is endemic to Australia.

<span class="mw-page-title-main">Centralian blue-tongued skink</span> Species of lizard

The Centralian blue-tongued skink or Centralian blue-tongue is a species of skink, occurring predominantly in the far north-west corner of New South Wales, Australia. It is one of six species belonging to the genus Tiliqua; the blue-tongued skinks and the shinglebacks.

<span class="mw-page-title-main">Tree-crevice skink</span> Species of lizard

The tree-crevice skink or tree skink (Egernia striolata) is a species of skink, a lizard in the family Scincidae. The species is endemic to Australia and is found in the states of Victoria, the Northern Territory, Queensland, New South Wales and South Australia. E. striolata tend to live in crevices and cracks in hollow logs or rocks. They greatly prefer heterogeneous and structurally diverse habitats and their behavior changes depending on the habitat they live in.

<span class="mw-page-title-main">Hosmer's spiny-tailed skink</span> Species of lizard

Hosmer's spiny-tailed skink or Hosmer's skink is a species of large skink, a lizard in the family Scincidae. The species is a diurnal, rock-dwelling species native to Northern Australia.

<span class="mw-page-title-main">Black rock skink</span> Species of lizard

The black rock skink is a species of large skink native to Eastern and Southern Australia from central New South Wales to Grampians National Park in Victoria. A large, dark colored skink, up to 135 mm from snout to base of the tail, the black rock skink is the first reptile discovered to have a "nuclear family" structure where the parents form a pair and care for their offspring for more than one year. The black rock skink is a viviparous skink meaning females give birth to live offspring instead of laying eggs. They defend their home range and families against conspecifics for up to several years.

The saltbush slender bluetongue is a species of lizard in the family Scincidae. The species is endemic to the arid interior of eastern Australia. Although its conservation status is of least concern, it has been listed as endangered in New South Wales. The slender saltbush bluetongue has been recorded in Sturt National Park in New South Wales but extends into northeast South Australia and south-west Queensland.

Egernia douglasi, also known commonly as the Kimberley crevice-skink, is a species of lizard in the family Scincidae. The species is endemic to Australia.

<span class="mw-page-title-main">Desert egernia</span> Species of lizard

The desert egernia, unadorned desert-skink or desert skink is a species of skink, a lizard in the family Scincidae. The desert egernia is endemic to the continent of Australia, and is widespread, with populations recorded in all mainland states and territories except the Australian Capital Territory. The desert egernia is found in dry, desert areas with deep, uncompacted sandy/loamy soils and little significant vegetation cover.

Slater's desert skink, also known commonly as the Centralian Floodplains desert-skink, Slater's egernia, and Slater's skink, is a species of lizard in the family Scincidae. The species is endemic to Australia. There are two recognized subspecies.

References

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  14. Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). The Eponym Dictionary of Reptiles. Baltimore: Johns Hopkins University Press. xiii + 296 pp. ISBN   978-1-4214-0135-5. (Egernia stokesii, p. 255).
  15. De Vis (1884).
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Further reading