Carlia

Northern red-throated skink Carlia rubrigularis, copyright Greg the Busker.

Belongs within: Lygosominae.

All the skinks of the rainbow
Published 24 June 2016

Australia is home to a diverse and distinctive array of reptiles, most of which are unique to the continent. Perhaps the most famous of these are its venomous snakes and gigantic crocodiles, but the continent also possesses its fair share of lizards. Among these are the subjects of today’s post, the rainbow skinks of the genus Carlia.

Breeding male southern rainbow skink Carlia tetradactyla, copyright Will Brown.

Carlia is primarily a genus of the north of Australia, particularly northern Queensland. They are moderately-sized skinks, with a snout-to-vent length of up to seven centimetres (indicating a total length of about half a foot). The vernacular name ‘rainbow skink’ refers to the bright colours, red, green, blue and/or black, exhibited by males of this genus during the breeding season. Females (and non-breeding males) are duller in coloration and commonly have a white stripe along the side of the body (Dolman & Hugall 2008). Only one of the more than twenty Australian species, the southern rainbow skink C. tetradactyla, is found in the southern half of the continent (specifically in a band from southernmost Queensland to northern Victoria). More than a dozen other species are found in New Guinea and neighbouring islands of eastern Indonesia; one species, C. peronii, is found on the island of Timor. Many Carlia species are difficult to distinguish without close examination and new ones continue to be described on a regular basis.

Closed-litter rainbow skink Carlia longipes (perhaps a non-displaying male?), copyright Greg Schechter.

Carlia can be easily distinguished from most other skink genera in the region by counting the toes, of which there are four on the forefoot and five on the hind foot (Storr 1974). Some authors have included all such Australo-Papuan skinks in this genus, but following a molecular phylogenetic analysis Dolman & Hugall (2008) recognised three genera of four-toed skinks in Australia: Carlia and the two smaller genera Lygisaurus and Liburnascincus. Lygisaurus species are generally more slender than Carlia and often have smaller legs. Liburnascincus includes three species of large skinks with sprawling legs found living around rocks. Both these genera lack the contrast in coloration between the sexes found in Carlia; at most, male Lygisaurus will become reddish around the head or tail.

Male rainbow skinks maintain territories from which they will vigorously exclude other males; a male may hold the same territory for several years (Langkilde et al 2004). Breeding males display themselves by flattening the body and tilting to one side, in order to optimise their apparent size and strikingness. Of the two Carlia species for which behaviour has been studied in detail, the black-throated rainbow skink C. rostralis is most likely to perform this display to other males, presumably as an act of intimidation. The lined rainbow skink C. jarnoldae, on the other hand, is more likely to perform its tilting display in the presence of a female (Langkilde et al. 2003). They may also display in this way towards predators, presumably to make themselves appear less digestible. Other displays performed by rainbow skinks include moving the head to display the coloration of the throat, or flicking the tail (this latter appears to be primarily a defensive display, being performed in the presence of predators or encroaching males). Langkilde et al. (2003) also found rainbow skinks to ‘play dead’ when captured, a rare behaviour in skinks (though known from other lizards).

Admiralty brown skink Carlia ailanpalai, from Lardner et al. (2013). This species lacks the sexual dichromatism of other Carlia species.

Rainbow skinks are also present in islands of western Micronesia, where they have been introduced by human activity. They were first recognised in Micronesia in the early 1960s, subsequently becoming abundant and seemingly supplanting native skinks in more disturbed areas. On Guam, they are also believed to have played a part in the spread of the brown tree snake Boiga irregularis: the healthy population of introduced skinks provided a reliable food source for the introduced snake. Because of the aforementioned difficulties in Carlia taxonomy, the exact identity of Guam’s ‘curious skink’ was uncertain for many years though it was certainly part of the New Guinean ‘Carlia fusca‘ group. A molecular analysis of Micronesian Carlia by Austin et al. (2011) confirmed that the species in question was the Admiralty brown skink C. ailanpalai but also found that skinks from different parts of Micronesia where connected genetically to different parts of the New Guinean archipelago. Rainbow skinks from Guam, for instance, were related to populations on Manus and New Ireland, whereas Palau skinks were more closely akin to New Britain residents. Austin et al. noted a correlation between the sources of each of the inferred separate invasions in Guam, Palau and the Northern Marianas and troop movements during World War II. While machinery and equipment was being transported to Micronesia for use in the Pacific theatre of war, skinks were apparently hitching rides. Alternatively, some could have reached Micronesia with equipment being returned to permanent military bases from New Guinea after the war’s close. The resulting seed populations would have presumably been small, explaining why it took another twenty years or so before they were noticed.

Systematics of Carlia
Carlia Gray 1845 [incl. Heteropus Duméril & Bibron 1839 non Beauvois 1805, Myophila De Vis 1884]G74
|--*C. melanopogon (Gray 1845) [=Mocoa melanopogon]G74
|--C. aerata Garman 1901M52
|--C. albertisii Peters & Doria 1878M52
|--C. amax Storr 1974C18
|--C. atrigulare Ogilby 1890M52
|--C. beccarii Peters & Doria 1878M52
|--C. bicarinata Macleay 1877M52
|--C. blackmanni de Vis 1885M52
|--C. burnetti [=Ablepharus burnetti]G74
|--C. curta Boulenger 1897M52
|--C. decora Hoskin & Couper 2012C18
|--C. devisii Boulenger 1890M52
|--C. diguliense Kopstein 1926M52
|--C. dogare Covacevich & Ingram 1975C18
|--C. foliora de Vis 1884M52
|--C. fusca (Duméril & Bibron 1839)FR98, G74 [=*Heteropus fuscusG74]
|--C. gracilis Storr 1974C18
|--C. inconnexa Ingram & Covacevich 1989C18
|--C. insularis Afonso Silva, Santos et al. 2017C18
|--C. isostriacantha Afonso Silva, Santos et al. 2017C18
|--C. jamnana Loveridge 1948M52
|--C. jarnoldae Covacevich & Ingram 1975C18
|--C. johnstonei Storr 1974C18
|--C. laeve Oudemans 1894M52
|--C. lateralis de Vis 1885M52
|--C. leucotaenia Bleecker 1860M52
|--C. longipes (Macleay 1877)C18
|--C. luctuosa Peters & Doria 1878M52
|--C. maccooeyi Ramsay & Ogilby 1890M52
|--C. munda (De Vis 1885)C18
|--C. mundivense Browne 1898M52
|--C. nigrigulare Boulenger 1897M52
|--C. novaeguineae Meyer 1874M52
|--C. pectoralis (De Vis 1885)C18
|--C. peronii Duméril & Bibron 1839M52
|--C. pulla Barbour 1911M52
|--C. quinquecarinata (Macleay 1877)C18
|--C. rhomboidalis (Peters 1869)C18
|--C. rimula Ingram & Covacevich 1980C18
|--C. rostralis (De Vis 1885)C18
|--C. rubigo Hoskin & Couper 2012C18
|--C. rubrigularis Ingram & Covacevich 1989C18
|--C. rufilatus Storr 1974C18
|--C. schmeltzii (Peters 1867)C18
|--C. sembalunica Mertens 1927M52
|--C. sexdentata (Macleay 1877)C18
|--C. spinaure Smith 1927M52
|--C. storri Ingram & Covacevich 1989C18
|--C. tetradactyla (O’Shaughnessy 1879)C18
|--C. triacantha (Mitchell 1953)C18
|--C. tricarinata Meyer 1874M52
|--C. vertebrale de Vis 1888M52
|--C. vivax (De Vis 1884)C18 [=*Myophila vivaxG74]
`--C. wundalthini Hoskin 2014C18

*Type species of generic name indicated

References

Austin, C. C., E. N. Rittmeyer, L. A. Oliver, J. O. Andermann, G. R. Zug, G. H. Rodda & N. D. Jackson. 2011. The bioinvasion of Guam: inferring geographic origin, pace, pattern and process of an invasive lizard (Carlia) in the Pacific using multi-locus genomic data. Biol. Invasions 13: 1951–1967.

[C18] Cogger, H. G. 2018. Reptiles and Amphibians of Australia updated 7th ed. CSIRO Publishing: Collingwood.

Dolman, G., & A. F. Hugall. 2008. Combined mitochondrial and nuclear data enhance resolution of a rapid radiation of Australian rainbow skinks (Scincidae: Carlia). Molecular Phylogenetics and Evolution 49: 782–794.

[FR98] Fritts, T. H., & G. H. Rodda. 1998. The role of introduced species in the degradation of island ecosystems: a case history of Guam. Annual Review of Ecology and Systematics 29: 113–140.

[G74] Greer, A. E., Jr. 1974. The generic relationships of the scincid lizard genus Leiolopisma and its relatives. Australian Journal of Zoology, Supplementary Series 31: 1–67.

Langkilde, T., L. Schwarzkopf & R. Alford. 2003. An ethogram for adult male rainbow skinks, Carlia jarnoldae. Herpetological Journal 13: 141–148.

Langkilde, T., L. Schwarzkopf & R. A. Alford. 2004. The function of tail displays in male rainbow skinks (Carlia jarnoldae). Journal of Herpetology 39 (2): 325–328.

[M52] Mittleman, M. B. 1952. A generic synopsis of the lizards of the subfamily Lygosominae. Smithsonian Miscellaneous Collections 117 (17): 1–35.

Storr, G. M. 1974. The genus Carlia (Lacertilia: Scincidae) in Western Australia and Northern Territory. Records of the Western Australian Museum 3 (2): 151–165.

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