Marlborough green gecko

Naultinus manukanus, commonly known as the Marlborough Green Gecko^[3] or the Manuka gecko,^[4] is a small species of gecko endemic to New Zealand.^[4][3] The species' name, manukanus, was derived from this species being commonly found in Mānuka shrubs.^[4][3] The holotype is in the collection of the Museum of New Zealand Te Papa Tongarewa.^[5]

N. manukanus is usually bright green.^[3] The dorsal surface of N. manukanus is a uniform green which is sometimes paired with small paler spots.^[3] These spots can be pale green, yellow, or white.^[6] Instead of spots, these geckos may have thin markings on either side of the midline.^[3] N. manukanus also has enlarged conical scales, usually present on the snout, head, and along dorsolateral surfaces.^[3][6]

Other identifying features of N. manukanus include a lavender/pink or orange mouth lining that has either a pink or yellow tongue.^[3] N. manukanus has narrow toes compared to other species which may have expanded toe pads.^[3] The underside of this species’ feet is also yellow in colouration.^[3]

The pattern of N. manukanus is variable depending on its geographic location.^[3] The variation in geographic location also causes variation with the enlargement of the conical scales.^[3] Populations from the outer Marlborough sounds are uniform green and usually have few enlarged scales, whereas populations further south have more variable patterns and colours along with distinctive enlarged scales.^[3] Some N. manukanus are entirely yellow; this is called a xanthic form.^[3]

N. manukanus can be distinguished from most South Island Naultinus due to its plain pattern and more uniform colouration,^[3] with the exception of the jeweled gecko (N. gemmeus) and starred gecko (N. stellatus).^[3] N. manukanus can be distinguished from all other species of Naultinus through its enlarged conical scales which cover the head, nape, and dorsolateral regions.^[3] This excludes the rough gecko (N. rudis) which is a close relative of N. manukanus.^[6] N. rudis has enlarged conical scales that cover its entire body compared to the selected areas of N. manukanus.^[3][6] N. manukanus also have a different mouth and tongue colour while the males have different belly colours.^[3][6]

N. manukanus is a sexually dimorphic species, with males and females differing in ventral colour and size.^[3] Males are typically smaller than females with a snout to vent length (SVL) of 64-68 mm, whereas females have a SVL of 69-79 mm.^[3] The ventral surface of an adult male is a pale blue-white, blue-green or silver whereas females can be distinguished by a pale yellow-green ventral surface.^[3]

N. manukanus is endemic to New Zealand.^[3][7] N. manukanus populations occur throughout the Marlborough region.^[3][8] Populations can be found as far south as the Wairau River and west to the Bryant and Richmond ranges.^[3][8] Populations of N. manukanu have also been recorded throughout the islands of Marlborough sounds such as Arapawa island.^[3] There are also successful translocated populations on Motuara island and Wakaterepapanui island.^[3][8]

N. manukanus usually inhabit coastal and lowland regions.^[3] They are commonly found inhabiting coastal and lowland forests, shrublands as well as Muehlenbeckia thickets.^[3] N. manukanus is commonly found in Mānuka shrubs, which is reflected in its species name, manukanus.^[3][9] N. manukanus also appears to inhabit scrubby and regenerating habitats often, although that may be due to easy access.^[8]

N. manukanus is quite long lived like most of the reptile species in New Zealand.^[8] They can live up to 30 years or possibly more; the captive record for N. manukanus is 30 years.^[3]

N. manukanus populations may exhibit a female-biased sex ratio at birth based on a 25-year study of a population on Stephans island.^[9] The breeding season of N. manukanus occurs between June and October (observed in captivity). The females are viviparous and usually give live birth two young between February and April.^[3][8][9] The gestation period of these offspring is approximately 7.5 months.^[8] These young measure 26-35 mm in SVL, reach maturity within 1-2 years, and are fully grown around 3-4 years of age.^[3][8][9]

Males exhibit mate guarding behaviour which includes following the females around.^[8] They also display aggressive behaviour towards others within their genus, which is during the breeding season.^[8] During the mating process, as in many other gecko species, the male bites the female's neck and head repeatedly as he mounts her.^[8]

N. manukanus is cathemeral (active both day and night), although it is predominantly diurnal (day-active) and is heliothermic, meaning they require heat by basking under the sun.^[3][8][9] N. manukanus is arboreal, which explains its prehensile tail.^[8]

They are visually cryptic due to their foliage-matching colouration, and usually remain hidden through their slow movement.^[9] The crypsis of N. manukanus stems from the native birds being one of their main forms of predators.^[10] Birds rely on visual cues from a distance and being visually cryptic is a great form of predator avoidance.^[10] N. manukanus are also known to vocalize a barking sound and mouth gape at potential predators and threats.^[8]

Movement of N. manukanus is usually associated with moving to a warmer/sunnier spot or retreating into vegetation during harsher weather.^[3] N. manukanus moves less on cloudy days and are usually found under the foliage, whereas on clear days they are more active and are usually found basking atop the foliage.^[9]

N. manukanus is solitary in nature, like most geckos, although they are found in large densities in some habitats.^[8] The neonates (babies) of N. manukanus are commonly found together and with their mothers for the first couple months of their lives, even though they are independent at birth.^[8]

N. manukanus uses a sit-and-wait foraging strategy where they lie in wait for unsuspecting invertebrates.^[3] They heavily rely on visual cues to use this type of foraging strategy.^[10]

N. manukanus are omnivores yet are primarily insectivorous.^[8] They are known to feed on the small fruits of several plant species and have also been known to feed on nectar.^[10][11] N. manukanus diet suggests that they may also use chemoreception to detect food sources.^[10] Due to their arboreal lifestyle their invertebrate prey is composed of moths, flies, spiders, and beetles. They will also consume any other insect that may be present in the foliage.^[8]

N. manukanus previously had few predators except for avians and one reptile (Tuatara) until mammals were introduced.^[10] The introduction of predatory mammals has led to a large decline in N. manukanus populations.^[9] These predatory mammals include hedgehogs, mustelids, possums, and rats.^[9]

N. manukanus have been found infected with ectoparasitic mites in the wild.^[12] In a sample group of geckos, nine N. manukanus were found to have mites.^[12] Although ectoparasitic mites were found on N. manukanus it is still quite uncommon for them to be a host.^[8][12] Red mites have also been recorded in captive N. manukanus.^[8]

The fungus Mucor ramosissimus has been recorded in N. manukanus.^[13] Mucor ramosissimu causes black powdery lesions of necrosis and mycotic dermatitis within N. manukanus.^[13] The fungal infection of Mucor ramosissimu also causes mycotic osteomyelitis (a bone infection caused by fungi).^[13] Protozoal intestinal parasitism by Trichomonas sp. and Nyctotherus sp. has also been recorded within N. manukanus, causing weight loss and loss of appetite.^[13] A combination of the intestinal parasitism and fungal infection has led to the death of two N. manukanus (a male and a female) who were reported as dying from mycotic dermatitis with digital gangrene, and osteomyelitis.^[13]

Other species of Naultinus have been recorded with disecdysis (shedding issues) and pseudobuphthalmos (build-up of liquid in the spectacle of the eye).^[8] These conditions may also affect N. manukanus because they have been documented within the same genus.^[8]

N. manukanus is closely related to N. rudis (rough gecko); they are sister taxa.^[14] They are both part of the Naultinus genus yet were previously part of the Heteropholis genus.^[6] N. manukanus and N. rudis both share a similar feature of large conical scales.^[3] N. rudis has more enlarged conical scales which covers its entire body, compared to N. manukanus, which easily differentiates them.^[3][6] N. manukanus' next closest relative is the starred gecko (N. stellatus), whereas the west coast green gecko (N. tuberculatus) is the sister to the group.^[14]

N. manukanus have been known to feed on small fruits and occasionally the nectar of flowers.^[10] This is a common feature of New Zealand geckos and skinks and plays a part in plant pollination and seed dispersal.^[11] Geckos (and skinks) were once a part of important plant reproduction in New Zealand.^[11] N. manukanus as well as other New Zealand species would disperse seeds from the fruits they consumed up to 20 meters away from the parental plant, allowing germination at a safe distance.^[11] Consumption of nectar from flowers would occasionally deposit pollen onto the geckos that would be transported to another flower which would then be pollinated.^[11] This was seen in Dactylocnemis geckos but suggests that N. manukanus may play a role in pollination.^[11]

In 2012 the Department of Conservation classified the Marlborough gecko as At Risk under the New Zealand Threat Classification System.^[8] It was judged as meeting the criteria for At Risk threat status as a result of it having a low to high ongoing or predicted decline. This gecko is also regarded as being Conservation Dependent. Populations have been threatened through habitat loss/destruction, habitat fragmentation, and the introduction of introduced mammalian predators including rats, mice, mustelids, and possums.^[9] N. manukanus populations also struggled with competition for food sources against introduced vespulid wasps.^[9]

• New Zealand Herpetological Society Page on Marlborough gecko