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Nactus simakal, gecko evolved in geomorphological habitat of Dauan Island

NEWS - Researchers report a new species of Nactus simakal that lives in a boulder-strewn habitat with deep crevices on Dauan Island in the northern Torres Strait. The Torres Strait Islands lie between Cape York Peninsula, north-eastern Australia, and the southern coast of Papua New Guinea and are rare in gecko biodiversity.

Nactus simakal, gecko evolved in geomorphological habitat of Dauan Island

The vertebrate fauna of the islands is a mix of Australian and New Guinean species with only two endemic species described to date. Conrad Hoskin of James Cook University in Townsville and colleagues describe the new species as highly distinctive based on ND2 mtDNA genetics and morphologically on its slender, elongated striped pattern.

N. simakal is broadly similar to Nactus galgajuga (Ingram, 1978) which is restricted to a boulder-strewn habitat about 750 km to the south in mainland north-eastern Queensland, but is easily distinguished morphologically and genetically from saxicolines.

N. simakal is the second vertebrate species to be described and considered truly endemic to the Torres Strait islands. Another species, the extinct Bramble Cay Melomys Melomys rubicola, is only known to have occurred on Maizab Kaur in the north-eastern corner of the Torres Strait.

The rainbow lizard Carlia quinquecarinata is from the Erub and Mer Islands but may also have occurred on Dauan Island and the adjacent mainland of New Guinea. It is likely that N. simakal is restricted to Dauan Island due to its dependence on the island's granite geomorphology.

This geomorphological habitat does not occur on Saibai and Boigu Islands or the flat, rockless southernmost parts of New Guinea. Surveys of other Torres Strait islands have found N. eboracensis and N. cf. papua, but neither of these species has been found on Dauan Island.

N simakal's striped pattern, slender form, large eyes, 'beaked' face and, long slender tail are likely adaptations similar to the saxicoline lifestyle in boulder-strewn habitats, while N. galgajuga occupies exposed granite boulder fields.

Interestingly, Saltuarius eximius Hoskin & Couper (2013), a leaf-tailed gecko that lives on granite boulders at Cape Melville also has a slender, beaked face and large eyes. N. simakal does not appear to be closely related to N. galgajuga, and the similarities in morphology and pattern are likely the result of independent evolution.

Phylogenetically for ND2, N. simakal is in a clade containing N. eboracensis from Cape York Island and the Torres Strait, and N. alotau from the southeastern coast of Papua New Guinea. Genetic data are not available for N. c.f. papua and N. inundatus which are distributed in the Torres Strait and southern Papua New Guinea respectively.

N. simakal and N. alotau have keeled subcaudal scales, while N. eboracensis has smooth subcaudal scales. In another clade, N. kunan from the Admiralty Islands has keeled subcaudal scales and two Australian species, N. cheverti and N. galgajuga, have smooth subcaudal scales. In both clades, the basal species have keeled subcaudals.

Hoskin and team recommend further phylogenetic investigations for Australo-Papuan Nactus that are much more comprehensive, including many nuclear genes and more New Guinea populations of the species, to shed light on the biogeographic and morphological evolutionary history of this vertebrate group.

Original research

Conrad J. Hoskin, Alexander Davies & Kieran Aland (2024). A new species of Nactus gecko from boulder-pile habitat on Dauan Island, Torres Strait, Australia. Zootaxa 5497 (4): 577–590 DOI:10.11646/zootaxa.5497.4.7
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