The Shingleback Skink (Tiliqua rugosa) is a heavily armored, blue-tongued skink. It has a short stumpy tail and can range in colors from dark brown to light yellow. It inhabits the arid and semi-arid regions of western and southern Australia. It is viviparous and mostly monogamous. It has been known to pair with the same mate for up to 20 years. It has an omnivorous diet, consuming vegetable matter as well as insects and snails. It is preyed upon by dingos, pythons and feral cats that were recently introduced into Australia. Unlike most skinks, T. rugosa does not exhibit tail autotomy.
Tiliqua rugosa is currently one of the more abundant reptles that inhabits Australia. They range throughout the drier parts of Southern Australia, from approximately Bathurst in New South Wales all the way to the coast of Western Australia. T. rugosa is, for the most part, exclusive to the above areas and is never found naturally in the highly populated southeastern coast or any portion of Northern Australia (Walls, 1996).
Biogeographic Regions: australian (Native )
Tiliqua rugosa can be found in Southern and Western Autralia, reaching north up to Caravorn, the outer wheatbelt, Kalgoorlie and the Nullarbor Plain. Some populations can also be found in Southeastern Australia (Storr et al. 1981). The type locality is King George Sound, Western Australia (Worrell 1963).
Distribution: Australia (S West Australia, S South Australia, Victoria, New South Wales except coastal areas, S/C Queensland) asper: E Australia rugosa: W Australia konowi: Rottnest Island, West Australia. palarra: West Australia, Shark Bay area.
Shingle back skinks are among the largest of the Australian skinks. Mature adults typically weigh 600 to 900 grams and have snout-vent lengths (SVLs) of 16 to 18 inches (VItt and Pianka, 1994). Tiliqua rugosa has an extremely short, blunt tail, being only one quarter of the SVL. The tail very much resembles the head of this species, and could probably be very easily as such by a would be predator. The scales of the body and tail are typically very large in size, and have a rough, knobby appearance, making this creature greatly resemble a pine cone. Head scales are fragmented and irregular, making them difficult to count and compare to other reptiles. The tongue of T. rugosa is cobalt blue in color, and is used extensively as a sensory organ, in conjunction with the Jacobson's organ. The dentation of this species is acrodont, meaning that the teeth are set on the edges of the jaw bones and are not in grooved sockets (Bustard, 1970). The legs in the shingle back skink are noticeably reduced, with the hind limbs being approximately twenty percent of the SVL, and the toes are short and fat (Cogger, 1975). Ear-openings are conspicuous and without anterior lobules (unlike genus Tiliqua). It is thought that males have a more slender, slightly longer tail than females, although this is by no means a sure way to sex this species. A better way of sexing is by cloacal examination (male hemipenes can be everted with pressure).
Coloration can vary greatly in the shingle backs, with three subspecies being recognized by these differences: T. r. rugosus of western Australia is classified as having a moderately long, slender tail and is brownish-red in color with yellow spots or white bands; T. r. konowi of Rattnest Island is small and dark, with gray coloration and numerous tiny, white specks on the belly and back; and T. r. asper of eastern Australia has the shortest, widest tail, with a very fragmented scalation pattrn and is usually solid brown with no pattern at all (Walls, 1996).
Range mass: 600 to 900 g.
Other Physical Features: heterothermic
Tiliqua rugosa is a heavily-bodied lizard with large pine-cone-like scales. Its limbs are small relative to the rest of the body. Its short, wide, stumpy tail resembles its head, and may be used to confuse predators. It contains fat reserves, which are consumed during winter hibernation or periodic droughts. The tail grows greatly in size after the lizard eats in abundance, and can become very thin during droughts (Bustard 1970) The head size is larger in males than in females (relative to body size), presumably for head-butting in intraspecific combat (Bull and Pamula 1996). The armored skull has lost the kinetic capability characteristic of most skinks (De Vree & Gans 1987).
The midbody scales are arranged in 21 to 32 rows. The dorsals are large and have a rough texture. The nasal scales are often separated but can sometimes be in contact. The prefrontals are almost always in contact, and only very rarely separated. There are usually 5 or 6 supracilliaries, and 9 or 10 upper labials (Storr et al. 1981).
This skink's skin color varies a lot among individuals and subspecies. The underside is white or creamy with blackish flecks, spots or blotches. These sometimes align into longitudinal streaks. The head and back are commonly orange-brown to brown and have cream-colored spots, blotches or streaks that sometimes form oblique bands (Storr et al. 1981). In Western Australia, the heads of Shinglebacks tend to be more prominent and attractively coloured with reddish brown and salmon. Tiliqua rugosa's pineal eye is more developed than that of the New Zealand tuatara (Worrell 1963).
A Shingleback with two heads and two sets of forelegs, was found in Coogee, New South Wales (Phillips, T. 2010).
Measurements from Storr et al. (1981):
Snout to vent length (SVL): 124-310 mm (mean: 238 mm).
Tail: 19-37% of SVL (mean: 27 mm).
Bustard (1970) claims that individuals can grow to be 18 inches (457mm) in length.
It can be distinguished from other Australian skinks of similar size by its short stumpy tail and large coarse scales.
The konowi subspecies is characteristically smaller and darker than the other subspecies, having an upper slaty grey surface, with an even distribution of small white spots. Its undersurface is dark and is also covered with small white spots (Storr et al. 1981).
Tiliqua rugosa inhabit semiarid plains and woodlands that typically have a harsh, dry summer and fall, followed by a cool winter and spring with increased precipitation and resources. These areas are subject to a great deal of variability in precipitation (Bustard, 1970).
Terrestrial Biomes: chaparral
Tiliqua rugosa is a primarily terrestrial lizard, though it can climb wire mesh and low tree stumps. Its typical home range is much smaller than those of predaceous lizards of similar size. It is usually found in arid and semi-arid plains, and bush lands, alongside roads or open areas within its range. During its hibernation period, it lives in burrows or rabbit warrens.
It will usually remain in its home range for at least five years, before moving to a different one. Its size or sex does not affect its fidelity to the home range (Bull & Freake 1999).
The shingle back is an omnivore that would be considered an opportunistic feeder. Its main diet typically consists of vegetable matter, such as herbs and seedlings, with any blossoms or fruits that it may come across included. The rest of the diet can consist of insects and other arthropods, snails, carrion, and basically any other edible thing that it is fortunate enogh to come across (Cogger, 1975). One of the greatest hardships that T. rugosa is adept at overcoming are periodic droughts and famines Typically, much food is available during the spring months after the winter rains, but that soon plummets during the following summer and fall months. As was discussed above, the tail acts as a fat store to help the shingle back survive in times if little or no sustenance. Its opportunistic feeding habits also aid in its survival (although the tendency to venture out into the road to consume carrion and then be struck and killed by motor vehicles is a leading cause of death in this species) (Vitt and Pianka, 1994).
Tiliqua rugosa's diet includes snails, insects, herbage, fruit and blossoms (Worrell 1963). It may eat larger amounts of plant matter than any other species in its genus (Greer 1989). Its predators are pythons, dingos and recently introduced feral cats.
Some populations are infested by the ticks Aponomma hydrosauri and Amblyomma limbatum. Lizards with high tick loads in a given year tend to have high loads in the the next year. Being in a pair increases the likelihood of having ticks. These ticks appear not to reduce the fitness of their hosts, and longevity and size may even be positively correlated with tick load (Bull and Burzacott 1993).
Diseases and Parasites
The shingleback skink is prone to acquire endemic diseases or parasites when in captivity (Worrell 1963). In the wild, some individuals have been found to be infected with a haemogregarine blood parasite (Hemolivia mariae). Such individuals tend to have smaller home ranges than uninfected individuals. However, experiments have shown that individuals with larger ranges are more susceptible to infection. Bouma et al. (2007) suggest that there is a trade-off between parasite defenses and physical activity. Lizards that are more active have larger ranges. Consequently, these get infected with parasites and are forced to inhibit their activity and reduce their range.
Individuals tend to be uniformly distributed in their habitat (Walton & Dyne 1987). Henle (1990) estimated that the density of a typical population is about 1 individual per hectare (biomass of 0.8kg per hectare). Based on observations of a South Australian population, Bull (1987) produced a higher estimate: 2.7 individuals per hectare.
Life History and Behavior
Tiliqua rugosa is a slow-moving, docile skink with limited stamina (John-Adler et al. 1986). Within its range, it is prone to spend time in a small area for a long time, and then move suddenly to another small area that is distant from the first, but still inside the range (Greer 1989). It may exhibit aggressive territorial behavior against male intruders. Males are more aggressive than females and have been reported to fight when placed in the same spot. It has been observed basking in the morning, first exposing only the head, and then emerging completely, positioning its body at a right angle relative to the sun. It can sometimes make an arc with its body, to make solar energy converge on itself (Edwards 1978).T. rugosa does not exhibit tail autotomy, presumably because the tail is indispensable for survival during winter hibernation (as storage for fat reserves). It has powerful jaws, which produce a sharp bite, and tend to bite when handled by humans. It becomes tamer in captivity (Bustard 1970).
Foraging strategies change throught the year and among the sexes. During the two months before mating, when food is abundant, males forage using a time-maximization strategy, while females use an energy-maximization strategy. During droughts, males and females significantly reduce their activity (Kerr & Bull 2006). When in pairs, the male eats significantly less than the female and remains a few centimeters behind the female during feeding, while the female eats just as much as when alone. This behaviour presumably suggests that males are on the alert for the presence of rival males when paired (Bull & Pamula, 1996). Moreover, a female can detect approaching danger earlier in a pair than when it is alone, and when in pairs, earlier when the male partner is not feeding. Bull and Pamula (1998) suggest this enhanced vigilance is a product of the combined perception of both partners in the pair. The behavior may be an adaptation for avoiding large predators when plant food is only available at exposed sites.
Young offspring of this species are able to discriminate between kin and non-kin, even when separated from their mothers at birth. They preferentially direct attention and tongue flicks to related over non-related individuals. In addition, foster mothers tend to spend more time with their own young (with which they are not familiar) than with familiar foster young. The mechanism behind this mother-offspring recognition system is unknown, but probably involves olfactory cues (Main & Bull 1996).
Tiliqua rugosa's visual range for a 0.5-m-high bush is approximately 20 m (Auburn et al. 2009). As it lives in uncleared chenopod shrub land, shelter bushes are about 10.5 m from any point in its home range, well within its perceptual range. A study by Freake (2001) found that it can use celestial cues as a navigational strategy to return to its home range. It detects these cues using its parietal eye, perhaps functioning as a celestial compass.
This skink hibernates during the summer months to escape the heat, living in burrows or rabbit warrens (Bustard 1970, Greer 1989).
Thermal and day-night cycles are regulated by cycles of melatonin production in the pineal complex (Firth, Kennaway & Belan 1991).
Embryos of Tiliqua rugosa have distinguishable light crossbands on their body, which acquire a darker tone before birth (Gadow 1901, as cited in Greer 1989).
The shingle back skink has an average life span of about 10 to 15 years, although there is a living and healthy specimen which resides as a captive in England (his name is Stumpy), that is an amazing 35 years old! However, that is extremely rare and would be even more rare in the wild (Walls, 1996).
Status: captivity: 14.5 years.
- Walls, J. 1996. Blue-Tongued Skinks. NJ: T.F.H. Publications,Inc..
Tiliqua rugosa has an average life span of more than 10 years (Bull 1987). A specimen caught by Holmes and Light (1983) was estimated to be 20 years old.
Lifespan, longevity, and ageing
Tiliqua rugosa are viviparous, typically producing 1 to 2 young, although triplets do occasionaly occur. A type of placenta very much like that of primitive mammals is formed between the mother and young. This permits the exchange of food and waste between the mother and the developing embryos (Cogger, 1967). Young are produced in late March or early April of each year after approximately 5 months of gestation. Young lizards weigh about 60 to 140 grams at birth and have a relative clutch mass (as a percentage of female gravid mass) of about 28%. The small litter size of young but the large size of individuals is believed to reduce risk of predation and aid in the potential survival through the oncoming winter months (Vitt and Pianka, 1994). Copulation is usually observed around late October or early November and is typically over with very quickly. There is a great deal of evidence that shingle backs are monogamous (see behavior section).
Tiliqua rugosa reaches sexual maturity in its third or fourth season of life (Bamford 1980, Greer 1989). The mating season occurs during the spring, but testicular and ovarian activity may being before the spring (Bourne, Taylor & Watson 1986). Mating is performed by the male grasping the female by the head, neck or shoulder using his mouth (Hitz 1983).
Monogamous pairs of T. rugosa are reported to have been found together after an interval of up to 25 years, and some have been continuously seen together for 3 years (Bull 1988, Greer 1989). Pairs can be frequently seen crossing the road in tandem during the spring, with the male following the female. The male attends the female until she is ready to mate and will remain with her afterwards for a sufficient time to ensure her eggs are fertilized by his sperm (Bamford 1980). An extensive study of monogamy in this species (using polymorphic microsatellite DNA loci to assess parenthood) revealed that most males are consistently monogamous, though some males mate with more than one female. There is also evidence of extra-pair fertilization in females, which appears to be more frequent in the females of polygynous males (Bull et al. 1989).
Tiliqua rugosa is viviparous, with a gestation period of 119-125 days (Hitz 1983). The typical clutch size is two (Worrell 1963) and the young are about half the parent's length. The newborn grow substantially in the spring after their birth, and they are large enough by the beginning of the summer to withstand adverse climatic conditions (Bustard 1970). If a young is born without any simultaneous siblings, it will likely be larger than if it is born in a pair. After birth, the young eats the mother's fetal membranes. The allantoplacenta is composed of the apposing fetal and maternal membranes, which are non-interdigitating (Bamford 1980, Greer 1989).
Evolution and Systematics
Within the genus Tiliqua, there are two distinct lineages. One contains species that are characteristically large and stout, with the head wider than the neck and a cross-banded skin pattern. The other contains species that are small, elongate and have a uniform color pattern. Tiliqua rugosa belongs to the first group, and is thus closely related to T. adelaidensis, T. gigas, T. multifasciata, T. nigrolutea, T. occipitalis and T. scincoides (Greer 1989).
Physiology and Cell Biology
Tiliqua rugosa has a salt gland in the nose that is under the control of hormonal corticosteroids and can excrete potassium and sodium in higher concentrations than normally found in the blood. It only becomes active when the body temperature reaches 30°C. It can respond to both sodium and potassium loading by selectively secreting the ion that is in excess (Braysher 1971). This gland is especially active in the spring and produces a white encrustation of salt around the nostril (Bradshaw et al. 1984). This species can also withstand wide fluctuations in the concentration of blood salt, ranging from 152 to 240 mEquiv/l, thus remaining alive in periods of drought. During such periods, it is able to completely shut down its kidneys (Bentley 1976, Walton & Dyne 1987, Greer 1989).
As in mammals and other Australian skinks, T. rugosa's parathyroid gland controls phosphate and calcium levels. It is paired and located at the base of the carotid arteries (Clark 1970). The adrenal glands are slender, are attached to the mesentery of the gonad and have been reported to be a major secretor of progesterone (Bourne 1981, Walton & Dyne 1987).
In males, androgens peak at the time of mating (Bourne & Seamark 1978). In females, progesterone reaches high levels during pregnancy, peaking during the middle third of the gestation period (Bourne et al. 1986).
Tiliqua rugosa are quite common in Australia and do not suffer from many natural predators. Road side killings tend to be the most devastating force on wild populations. A study of percent population loss of this species due to road kill was conducted and the results showed an average annual 11.9% population loss. These results greatly contrasted with an estimate by Ehmann and Cogger (1985) that 0.014% of all mortality in Australian herpetofauna is dure to road kills. This suggests that T. rugosa is very susceptible to this form of mortality, probably due to their feeding habits outlined above.
The conservation status of this species has not yet been reviewed by the International Union for Conservation of Nature (IUCN).
Relevance to Humans and Ecosystems
There are no known negative impacts of this species on humans.
Aboriginals have found T. rugosa to be a good source of food and some southern tribes of Australia used them medicinally. They are believed to kill and eat snakes, which has been witnessed but is not typical behavior(Serventry, 1977). The shingle back skink also plays a small part in the world pet trade. Exportation of this species from Australia is currently prohibited but there are some pairs in the trade that have been producing captive young for private collections. These captives command a high price and are fairly rare to come across.
Tiliqua rugosa is a short-tailed, slow moving species of blue-tongued skink found in Australia. Three of the four  recognised subspecies are found only in Western Australia, where they are known collectively by the common name bobtail. The name shingleback is also used, especially for T. rugosa asper, the only subspecies native to eastern Australia.
T. rugosa has a heavily armoured body and can be found in various colours, ranging from dark brown to cream. It has a short, wide, stumpy tail that resembles its head and may confuse predators. The tail also contains fat reserves, which are drawn upon during brumation in winter. This skink is an omnivore; it eats snails and plants and spends much of its time browsing through vegetation for food. It is often seen sunning on roadsides or other paved areas.
Apart from bobtail and shingleback, a variety of other common names are used, including stump-tailed skink, bogeye, pinecone lizard and sleepy lizard.
Etymology and taxonomy
The species was first described by John Edward Gray in 1825 as Trachydosaurus rugosus. It has since been reclassified as Tiliqua rugosa. Some herpetologists claim this species has more common names than any other lizard.
- T. r. rugosa: bobtail or western shingleback – Western Australia
- T. r. asper: eastern shingleback – eastern Australia
- T. r. konowi: Rottnest Island bobtail or Rottnest Island shingleback – Rottnest Island, Western Australia
Distribution and habitat
The species is widely distributed in arid to semiarid regions of southern and western Australia. The range extends from Shark Bay, Western Australia, across the southern-most regions of the country to the coast, then north into Queensland. Four subspecies are found in Western Australia, including one at Rottnest Island. It also occurs in the eastern states of Victoria and New South Wales, but does not reach coastal areas.
The habitat of the species includes shrublands and desert grasslands to sandy dunes. These skinks are well known, due to a preference for sun basking in open areas, and are often seen along roadsides or other cleared areas in its range.
T. rugosa has a heavily armoured body and can be found in various colours, ranging from dark brown to cream. Its snout to vent length varies from 260 to 310 mm (10 to 12 in), but it is a very heavy-bodied lizard for its length.
It has a triangular head and a bright blue tongue. Its short, stumpy tail is similar in shape to its head. This possibly evolved as a defence mechanism against predators, and has led to the common name of "two-headed skink". Its short tail also contains fat reserves, which the lizard lives upon during hibernation in winter. Unlike many skinks, shinglebacks do not exhibit autotomy and cannot shed their tails.
Tiliqua rugosa is an omnivore that eat snails, insects, carrion, vegetation and flowers. The species was once preyed upon by dingos, Australian pythons such as Morelia spilota, and local peoples; a threat is now more likely to come from large, introduced feral species, such as foxes and cats.
They have also been known to eat human food, such as sausage and chicken, as well as fruits such as banana and passionfruit.
The shingleback skink has become a popular pet among Australian enthusiasts.
T. rugosa is a viviparous skink, giving birth to broods of one to four relatively large offspring. Unlike most lizards, the species tends to be monogamous extending outside the breeding season of September through November; such pairs have been known to return to each other every year for up to 20 years.
Soon after birth, the young immediately consume their afterbirth. They stay with their parents for several months before moving on, but they remain in close proximity, forming a colony of closely related skinks.
Their hearing can be measured at the round window as cochlear microphonics and summating potential (of the cochlea), and compound action potential and single-fibre responses (of the auditory nerve).[jargon] These indicate a best hearing range near 1000 Hz. Earlier reports that their hearing sensitivity varied with the season, have been shown to be an artefact of the seasonally varying sensitivity to anesthetics.
Single unit recordings from the auditory nerve show both spontaneous and nonspontaneous responses. Tuning curves show peak sensitivity between 200 Hz and 4.5 kHz The absolute sensitivity is quite high, with some thresholds at 6 db sound pressure level, very close to human best sensitivity.
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