Naultinus

Naultinus is a genus of geckos that are endemic to New Zealand. On account of their striking colouration, species in the genus Naultinus are commonly known as green geckos. There are nine described species in the genus. Species in the genus share a number of traits that set them apart as quite different from the rest of the world's two thousand odd gecko species, which are generally brown in colour, ovivaparous, short-lived and nocturnal. In contrast, Naultinus are green, ovovivaparous, live up to 30 years or more and are strictly diurnal. New Zealand has a temperate, maritime climate, and in terms of distribution Naultinus is one of the southernmost gecko genera in the world — some species live in habitats in the South Island which receive regular snowfall in winter. Animals in this genus possess several physiological and behavioural adaptations to cope with these periods of low temperatures and adverse weather.
While historically widespread and quite common in areas of native forest all over the country, all species in this genus are of conservation concern in the present day. All nine species of Naultinus are declining in the wild and are much harder to find than they used to be; the populations of the various species are fragmented and approaching extinction, while others in the genus have already gone extinct. Entire populations of certain species, with unique traits and distinctive genetic profiles, have disappeared in the last 20 years. The primary known agents of this catastrophic decline include predation by invasive mammalian and avian species, habitat destruction and poaching for the illegal pet trade. Vespid wasp predation is speculated to be another possible contributing cause. Legal protection in the form of longer prison sentences for poachers caught with New Zealand protected species has been increased in recent years and translocations of various species to pest free islands have been undertaken with mixed results, but the task of saving these animals remains daunting. The behavioural and visually cryptic nature of these animals also pose challenges to their conservation management. The genus is, in general, in "dire need of research, particularly into factors that are causing their apparent decline", certain aspects of which remain unexplained.

Taxonomy

The following nine described species are recognized as being valid. A binomial authority in parentheses indicates that the species was originally described in a genus other than Naultinus.

Naultinus elegans – Auckland green gecko
Naultinus flavirictus Hitchough, Nielsen, Lysaght, & Bauer, 2021 – Aupouri green gecko, North Cape green gecko, yellow-lipped green gecko
Naultinus gemmeus – jewelled gecko
Naultinus grayii – Northland green gecko, Gray's tree gecko
Naultinus manukanus – Marlborough green gecko, northern tree gecko
Naultinus punctatus – Wellington green gecko
Naultinus rudis – rough gecko, natural tree gecko
Naultinus stellatus – Nelson green gecko, starry tree gecko
Naultinus tuberculatus – West Coast green gecko, Lewis Pass green gecko

Defining what constitutes a species among different populations within this genus has proved difficult and is still a matter of some scientific debate. Genetic evidence suggests that all nine species share an ancestor which is "very recent" in deep time terms and that hybridization between them is quite common. All species will interbreed in the wild, which has led some biologists to reject the notion of multiple Naultinus species and to instead view each "species" as a separate "race" or subspecies of a single, widespread species of this genus. However, there are a number of clear differences between recognized species in colouration, breeding times and even scale morphology. Multiple neighbouring species have slightly different mating seasons and behaviour, which is thought to explain why the species maintain their differences despite "strong reproductive compatibility". These differences are the basis for the present consensus in the scientific community that Nautilnus is constituted of nine species instead of nine races of a single species.
Genetically speaking, the jewelled gecko of the southern South Island is the most genetically distinct of the recognized species. In fact, it is thought that this species is the one that is ancestral to all other species in the genus. There are three distinct populations of N. gemmeus in Southland, Otago and Canterbury, differentiated by coloration and the time of their breeding seasons. In addition to recognizing gemmeus as one of a number of separate species within the genus, some biologists think that the three different populations of this species should be elevated to subspecies status to place more emphasis on their conservation management.

Description

Naultinus species are commonly known as "green geckos" in New Zealand for their striking bright green colouration. In addition, they are diurnal, which allows them to take advantage of warmer day-time temperatures. Both of these features are shared only with the day geckos of Madagascar. Almost every other type of gecko in the world is nocturnal and brown or grey in colour. All Naultinus are arboreal, and though most of them are predominantly green, their skin patterns are known to be plain, spotted, or striped. Occasionally, individuals of an overall lemon-yellow colour are encountered; this is a rare genetic colour morph similar to albinism.
The distinctive green colouration is almost universally predominant; with the two exceptions of male N. rudis as well as males of some populations of the Canterbury form of N. gemmeus, which are sexually dichromatic. While females are green, the males of N. rudis are grey with white and brown splotches, and in Canterbury, N. gemmeus females are always predominantly green as compared to the grey, brown or white males. The inside of the mouth, which is revealed in a threat display in some species, is deep blue, orange, pink or red. The broad fleshy tongue, which has a major function in cleaning the transparent scales which cover the eyes, is also brightly coloured; depending on the species it is red, orange, pink, yellow or black. The ears of New Zealand geckos appear as small openings on the side of the head behind the eyes, and the eardrum is visible a short distance inside this opening.
Naultinus species and indeed, New Zealand lizards in general, are conservative in their evolutionary development of scales. Most have the standard gecko-type scales which are small and granular, giving the skin a dull, velvety appearance. The two exceptions to this rule are two South Island members of the genus; the rough gecko and, to a lesser extent, the Marlborough green gecko. The rough gecko has enlarged conical scales which are both significantly wider and which protrude much further from the body than ordinary scales. These enlarged scales are scattered all over the body except for the underside of the animal. The Marlborough green gecko also has enlarged scales, but they are confined to the dorsal, pelvic area, and sometimes even in rows along the side of the animal. In any case, they are never found over all upper surfaces of the body as in the rough gecko.
All Naultinus species also possess long, finely tapered, strongly prehensile tails which they use as a "fifth limb" for grasping when they climb among the twigs and leaves of their arboreal habitat. They can hang by their tails if necessary. They also have comparatively slender toes, another adaptation to their arboreal lifestyle. The arboreal Naultinus use their toes in a grasping action on twigs and leaves, but there is some lamellar function as well.

Summary table of the key differences between ''Naultinus'' and ''Hoplodactylus''

There are multiple key differences in physiology and behaviour between species of NZ gecko in the two endemic genera, summarised in the table below:

Hoplodactylus	Naultinus
Mainly grey-brown	Mainly green
Nocturnal	Diurnal
Terrestrial, sometimes on tree trunks	Arboreal, on foliage
Active-prey-searching	Sit-and-wait predator
Generally fast-moving	Generally slow-moving
Can change intensity of skin colour	Skin colour intensity cannot be changed
Wide, non-prehensile tails, readily shed	Narrow, tapering prehensile tails, reluctantly shed
Some have wider toe pads with claws, adapted for climbing smooth, vertical surfaces	Thin toe pads adapted for grasping twigs and foliage

Distribution and habitat

The nine described species of Naultinus are found throughout the North and South islands of New Zealand and on a number of offshore islands. Historically, Naultinus species lived throughout the length of New Zealand, from the coast to as much as 1400 metres above sea level. However, all species have now undergone massive declines, and populations nationwide are fragmented and few Four species; elegans, grayii, flavirictus and punctatus are found only in the North Island. What was previously thought to be a distinct population of grayii, found only in the far north on the Aupōuri Peninsula has been determined from genetic work in the early 2000s to be a new species, more closely related, in fact, to elegans. It was described as N. flavirictus in 2021. The remaining five species: gemmeus, manukanus, rudis, stellatus, and tuberculatus are found only in the South Island. South Island Naultinus were, in the past, placed in a separate genus called Heteropholis but this taxon was abandoned when new genetic research in the 1980s showed little phylogenetic basis for this taxonomic division.
None of the Naultinus gecko populations are sympatric, presumably because each species is finely adapted to its local environment and also because their respective ecological niches are incredibly similar.