Oligosoma kahurangi, Patterson & Hitchmough, 2021

Patterson, Geoff B. & Hitchmough, Rodney A., 2021, A new alpine skink species (Scincidae: Eugongylinae: Oligosoma) from Kahurangi National Park, New Zealand, Zootaxa 4920 (4), pp. 495-508 : 500-506

Oligosoma kahurangi sp. nov.

Figures 4 , 5

Holotype. NMNZ RE008602 (adult male) Douglas Range , South Island, New Zealand; 41º 05’S, 172º 35’E; coll. A. Milne, 25 Nov 2019.

Paratypes (2 specimens). NMNZ RE008604 (adult female); same collection data as holotype ; NMNZ RE008603 (adult male); same collection data as holotype .

Diagnosis. O. kahurangi sp. nov. can be distinguished from other species in the genus Oligosoma by a combination of characters. These are: (a) interrupted subocular scale row; (b) unmarked cream ventral surface; (c) ITL>1.5 SVL; (d) MS>35; (e) clearly visible pale iris; (f) brown ground colour. It is most similar to O. longipes Patterson , O. hoparatea Whitaker et al. , and O. maccanni (Patterson & Daugherty) . It differs from O. longipes in having a median dorsal stripe which is either intact or broken (this is usually absent in O. longipes and where present has a herring-bone appearance not seen in O. kahurangi sp. nov.). There is no overlap in MS between O. kahurangi sp. nov. (36–38) and O. longipes (40–44) and O. hoparatea (40–43). Although very few individuals of each species have been observed, O. hoparatea appears to be a more robust animal than O. kahurangi ( Figures 4 and 7 ) and is substantially larger (maximum observed SVL is 91 mm in O. hoparatea compared with 69.9 mm in O. kahurangi sp. nov.; this equates to O. hoparatea being almost double the body mass of O. kahurangi sp. nov). Compared with O. maccanni the dorsal surface is 8 scale rows wide (6 in O. maccanni ) and the digits and tail are proportionally longer relative to SVL in O. kahurangi sp. nov. compared with O. maccanni .

O. kahurangi sp. nov. is found in high alpine (above 1400m) slate rock scree in a mountainous region with high rainfall and appears absent from nearby greywacke screes, whereas O. longipes occupies greywacke river terraces and screes at a wide range of altitudes in semi-arid inland basins in the rain-shadow of the South Island axial ranges.

Description of Holotype. Habit lacertiform, body elongate, oval in cross-section; limbs well developed, pentadactyl. Lower eyelid with a transparent palpebral disc, bordered on sides and below by small, oblong granules. Snout moderately blunt. Nostril centred in lower middle of nasal, not touching bottom edge of nasal, pointing up and back.

Supranasals absent; rostral broader than deep, contacts rostral, anterior loreals, prefrontals and frontal; frontonasal wider than deep, contacts rostral, anterior loreals, prefrontals and frontal, narrow contact with frontal; frontal longer than broad, similar length to frontoparietal and interparietal together, in contact with 2 anteriormost supraoculars; supraoculars 4, 2 nd largest; preoculars, 2, lower one larger; frontoparietals distinct, larger than the interparietal; a pair of parietals meeting behind interparietal and bordered posteriorly by a pair of nuchals and temporals, also in contact with interparietal, frontoparietal, 4 th supraocular, 2 postoculars, 1 temporal and 1 nuchal scale; loreals 2, posterior the larger; anterior loreal divided and in contact with 1 st and 2 nd supralabial, posterior loreal, prefrontal, frontonasal, and nasal; posterior loreal in contact with 2 nd and 3 rd supralabial, 1 st subocular, lower preocular, prefrontal, anterior loreal and 1 st supraciliary; supraciliaries 6, 6 th largest; 7 upper ciliaries, 6 th largest, forming prominent eyelid; 11 lower ciliaries; 6 suboculars, anterior largest, contacting subocular 2 nd and 3 rd, 4 th supralabial; subocular row interrupted by 6 th supralabial; 3 postoculars; 1 primary temporal, 2 secondary temporals; 3 tertiary temporals; supralabials 8, 7 th largest, 6 th supralabial under centre of eye; infralabials 6, several equally largest. Ear opening round, moderately large. Mental broader but shallower than rostral. Postmental larger than mental. Chinshields 3 pairs; anterior chinshields in broad contact, contact 2nd and 3 rd infralabials; second chinshields separated by one scale, contact 3 rd and 4 th infralabials; posterior chinshields separated by 4 gular scales, contact 4 th and 5 th infralabials; one scale between 3 temporals and ear opening; ear with 3–4 prominent triangular lobules on anterior margin, uppermost the largest. Dorsal scales similar in size to ventral scales, weakly striate; top of front feet with series of 2 enlarged scales in line with toes, scales on top of hind feet small; ventral scales and subdigital lamellae smooth. Adpressed limbs meeting; digits moderately long, subcylindrical; third front digit similar in length to 4 th.

Measurements (in mm; holotype with the variation shown in the specimens examined in parentheses). SVL 52.0 (mean 60.1, range 52.0–69.9); HL 9.6 (mean 10.4, range 9.6–11.3); HW 6.1 (mean 6.3, range 6.0–6.7); AG 23.0 (mean 28.9, range 23.0–36.7); SF 20.8 (mean 22.8, range 20.8–24.3); S-Ear 11.0 (mean 12.2, range 11.0– 13.1); EF 11.2 (mean 11.1, range 9.9–12.2); HLL 24.6 (mean 26.5, range 24.6–28.4); D-Ear 1.0 (mean 1.1, range 1.0–1.2); FTL 9.0 (mean 9.2, range 9.0–9.3).

Variation (holotype with the variation shown in the paratypes /specimens examined in parentheses). Upper ciliaries 7 (mean 7, range 6–7); lower ciliaries 10 (mean 11, range 10–11); nuchals 3 pairs (mean 2 pairs, range 1–3 pairs); midbody scale rows 38 (mean 37, range 36–38); ventral scale rows 93 (mean 92, range 91–93); subdigital lamellae 26 (mean 25, range 24–26); supraciliaries 6 (mean 6, range 6–6); suboculars 6 (mean 7, range 6–7). Frontonasal not usually separated from frontal by prefrontals meeting in midline. Anterior loreal usually in contact with first and second supralabial, posterior loreal usually in contact with second and third supralabial. Supralabials 8 (usual), or 7, the sixth or seventh largest. Infralabials 7. Projecting scales always present in ear opening. Maximum SVL 69.9 mm. Only 1 of the specimens examined had an intact tail: ITL/SVL = 1.75. Ratios for morphological measurements (± SD): AG/SF 1.26 ± 0.28; S-Ear/EF 1.11 ± 0.19; HL/HW 1.66 ± 0.08; SVL/HL 5.76 ± 0.39; SVL/HW 9.57 ± 1.0; SVL/HLL 2.26 ± 0.18; SVL/FTL 6.56 ± 0.94 (N=3).

Colouration. Four live specimens were examined for colouration and the description is as follows: Mid-dorsal stripe usually present, not usually continuous. This stripe becomes expanded and wavy down length of tail. Dorsal surface mid to dark brown, 8 scale rows wide, grading into pale dorsolateral stripe usually extending from above eye almost to tip of tail. This pale stripe extends into brown lateral stripe 2 scale rows wide, notched on upper and lower edges, running from behind nostril towards tip of tail, becoming flecked with light and dark on tail. This brown band is bordered on each edge by a dark brown band 1 to 2 half-scale rows wide running above the limbs and becoming indistinct after hindlimb. The lower dark brown band is bordered below by a pale stripe, 1 to 2 half-scale rows wide running from below the eye, through the ear, above the limbs to become indistinct after the hindlimbs. This band is bounded below by a darker band breaking up into a ventral pale colour. Soles of feet grey/cream. Belly and throat cream, unmarked. Outer surface of forelimbs brown, with a prominent pale stripe. There do not appear to be sexually dimorphic colour patterns.

Etymology. Named for Kahurangi National Park where the species is found. The name was decided in consultation with Manawhenua Ki Mohua. Recommended common name is the Kahurangi skink.

Distribution. South Island only, one single location in the Douglas Range. Confined to slate scree substrate at about 1500m altitude and approx. 8000m 2; apparently absent from nearby greywacke screes, which were searched without success by GBP and colleagues in 2018.

Natural History. Diurnal, strongly heliothermic, terrestrial. The highest densities were seen on slate scree—at one stage 7 were seen in an hour, between 8–9 am as temperatures started to rise. Smaller skinks were more common on the scree, while the largest specimens sighted were on the margins where there was mixed slate, Dracophyllum species and tussock habitat (Alec Milne pers. comm,). The only other lizard species which has been found at this site is the Kahurangi gecko ( Woodworthia ‘Mt Arthur’).

Discussion. Decisions on whether allopatric populations justify formal taxonomic recognition are essentially subjective and therefore problematic. O. kahurangi sp. nov. is phylogenetically a genetically divergent outlying population of O. longipes sensu stricto, found in inland Marlborough ( Figure 6 ). O. kahurangi sp. nov. is 2.9% divergent in ND2 sequence from O. longipes .

Intraspecific ND2 genetic distances of up to about 5% are not uncommon in New Zealand skinks. Strong justification is therefore necessary for specific recognition in allopatry at smaller genetic distances. We believe that justification exists for O. kahurangi sp. nov.

This species is very strongly divergent in morphology from O. longipes , given that many Oligosoma species are morphologically very conservative (this is reflected in the history of requiring modern genetic techniques to identify many cryptic species in the genus). Body proportions are different, scale counts are not just non-overlapping but well separated and colour (brown rather than greyish) and colour pattern (predominantly striped rather than predominantly speckled) are distinctly different ( Table 2). Ecologically the two species are quite different— O. kahurangi sp. nov. is found in high alpine (above 1400m) slate rock scree in a mountainous region with high rainfall and appears absent from nearby greywacke screes, whereas O. longipes occupies greywacke river terraces and screes at a much broader range of altitudes in semi-arid inland basins in the rain-shadow of the South Island axial ranges ( Patterson 1997). The two habitats (c. 120 km apart at their closest point) are separated by a zone of dense southern beech forest unsuitable for occupation by terrestrial heliothermic skinks.

The differences in morphology are likely related to long histories in different ecological settings, and therefore different evolutionary trajectories. Hare et al. (2008) and Chapple et al. (2009) place the separation of O. microlepis from O. smithi (3.6% corrected ND2 distance) in the late Pliocene. That would place the separation of O. kahurangi sp. nov. and O. longipes (2.9% corrected ND2 distance) in the very late Pliocene or early Pleistocene. Open habitat would have been continuous between the current ranges of the two species during Pleistocene glaciations; however, the genetic divergence between O. kahurangi sp. nov. and O. longipes suggests they have been isolated far longer than just since the last glacial cycle. This suggests that they maintained separate evolutionary trajectories on multiple occasions while there was potential for contact between them. They therefore fit the criteria for separate species status under the evolutionary ( Wiley 1978) and cohesion ( Templeton 1989) species concepts.

Another approach to determining whether O. kahurangi sp. nov. justifies separate species status is to compare its level of morphological divergence with that seen between related sympatric species. This approach has been used with birds (e.g. Tobias et al. (2010), summarised in Winker 2010)) but can easily be adapted to other taxonomic groups such as lizards. In this approach, if we can show that O. kahurangi sp. nov. is at least as morphologically distinct from O. longipes as O. longipes is from a sympatric closely related species then by inference O. kahurangi sp. nov. is also a full species. Fortunately, this scenario exists: O. aff. longipes “southern” is sympatric with O. hoparatea which is its sister taxon but reproductively isolated ( Whitaker et al. 2018). Despite being phylogenetically deeply divergent and not being sister taxa, O. longipes s.s. and O. aff. longipes “southern” are morphologically cryptic species. O. hoparatea can be distinguished from its sympatric congener by colour pattern and a few differences in scalation, most of which have not been used to differentiate New Zealand skinks previously. However, it overlaps in MS and VS scale counts—important known taxonomic characters in New Zealand skinks—in contrast to O. kahurangi sp. nov. and O. longipes ( Table 2). Also, based on observations of live animals, the intact tail lengths of the two sympatric species are similar, unlike O. kahurangi sp. nov. and O. longipes . The latter two species also differ in colour pattern.

Other examples of deeply divergent sympatric species with less morphological divergence than that between O. longipes and O. kahurangi sp. nov. are seen in the O. inconspicuum complex ( Chapple et al. 2011). O. burganae , O. repens , and O. toka are sympatric with and deeply phylogenetically divergent from O. inconspicuum but were previously not distinguished from that species, and the morphological differences among the four are minor.

On the other hand, there are several good precedents for recognition of distinct allopatric New Zealand skink species at similar levels of phylogenetic, morphological and ecological divergence to that between O. longipes and O. kahurangi sp. nov.: O. smithi-O. microlepis ND 2 3.6% ( Hare et al. 2008), O. pikitanga-O. judgei ND 2+ND4 3% ( Patterson & Bell 2009), O. notosaurus-O. inconspicuum ND 2 4.6% ( Chapple et al. 2011), O. salmo-O. albornense ND2 Tamura-Nei corrected distance 2.9% ( Melzer et al. 2019). The alpine black-eyed gecko Mokopirirakau kahutarae , has a broadly similar distribution in Nelson-Marlborough to O. kahurangi sp. nov. plus O. longipes sensu stricto. It is highly divergent in morphology from its broadly sympatric but lower-altitude sister species, the forest gecko M. granulatus , but is separated from it by an ND2 distance of 3.8% (Knox et al. MS).

O. kahurangi sp. nov. shares several characters with other saxicolous Oligosoma species, such as higher scale counts relative to similarly-sized non-saxicolous species and elongated digits and tail.

The colouration allows the species to be camouflaged in its rocky habitat. Potential predators of O. kahurangi sp. nov. include New Zealand falcon Falco novaeseelandiae Gmelin and introduced mammals (particularly feral house mouse Mus musculus Linnaeus and stoat Mustela erminea Linnaeus ). Other invasive mammalian predators (brushtail possum Trichosurus vulpecula (Kerr) , European hedgehog Erinaceus europaeus Linnaeus , ship rat Rattus rattus Linnaeus , Norway rat R. norvegicus (Berkenhout) , feral pig Sus scrofa Linnaeus, feral ferret Mustela furo Linnaeus , weasel M. nivalis Linnaeus and feral cat Felis catus Linnaeus ), and also invasive social insects are unlikely to be present at such high altitude in sufficient numbers to be a major threat.

Conservation status. O. kahurangi sp. nov. is currently known from a single very small site, although numbers at that site are reasonably high (e.g. 27 were seen between 23 and 25 November 2019 (A. Milne pers. comm.)). While the alpine areas of Kahurangi National Park have had little formal lizard survey, numbers of incidental lizard records from those areas supplied by trampers, climbers and conservation workers have been steadily increasing in the last two decades. Past records have been of one gecko and one skink species ( Woodworthia ‘Mount Arthur’, Oligosoma newmani ) from numerous locations scattered across the park, and three other gecko species and one skink ( Naultinus stellatus , Mokopirirakau granulatus , M. kahutarae , and Oligosoma polychroma ) from fewer sites, mainly at lower altitude except for M. kahutarae (DOC Herpetofauna database). No past records that we are aware of are likely to be referable to O. kahurangi sp. nov. This species is therefore very unlikely to be common and widespread, although it is very possible that additional undiscovered small isolated populations exist. We have no information on population trend.

In the New Zealand Threat Classification System, precautionary interpretation of currently available information suggests that O. kahurangi sp. nov. should be regarded as Nationally Critical on the basis of both criterion 1a (adult population of fewer than 250 mature individuals) and criterion 1b (area of occupancy of less than 1 hectare). Because no information exists on population trend, no detailed census has been carried out, and the likelihood of additional populations existing undiscovered is quite high, this listing should carry the qualifier “Data Poor”.

In the IUCN red-list system, the species is best regarded as Data Deficient. While it is reasonable to infer that the reproductively mature population is likely to be below the 250 threshold for inclusion in the Nationally Critical category in the New Zealand national system, it is unlikely to be below the threshold of 50 adults required for inclusion in the Critically Endangered category in the IUCN red-list in the absence of current or historical trend information. While its known area of occupancy is less than 10 km 2, and it exists at a single known locality, it is not known to meet the additional criteria (continuing decline or extreme fluctuations) for inclusion in Critically Endangered on the basis of area of occupancy. Extreme fluctuations do not apply for any of the moderately to very highly Kselected New Zealand lizards. Continuing decline is almost universal in mainland New Zealand lizard populations because of the impacts of invasive mammalian predators ( Hitchmough et al. 2016b). However, these effects appear to be somewhat ameliorated at high altitudes where the range of predator species present is reduced. In addition, O. kahurangi sp. nov. is sympatric with a population of the New Zealand rock wren ( Xenicus gilviventris ) which is being protected by targeted intensive control of invasive predators. This pest control may also be incidentally benefiting the skink population by suppressing stoat and possum numbers to low levels. However, mice ( Mus musculus ), which increase in abundance when larger pest mammals are controlled to low densities ( Wilson et al. 2018), are not under significant sustained control from these operations. They are serious predators of native lizards ( Newman 1994; Nelson et al. 2016) and may be causing ongoing decline in O. kahurangi sp. nov.

Survey and research requirements. Virtually nothing is known of this species beyond its existence. Survey of similar nearby habitats is required to assess its area of occupancy, and a census of the population at the single known site is required to better understand its conservation status and need for management. In the longer term, regular monitoring is needed to establish population trend, and to quantify any benefits of existing predator management and the possible impact of mice.

Figures

FIGURE 4. Holotype of O. kahurangi sp. nov. when alive.

FIGURE 5. Holotype of O. kahurangi sp. nov. in Te Papa Tongarewa, National Museum of New Zealand collection. (photo: Jean-Claude Stahl)

FIGURE 6. O. longipes, northern form. (photo: Bruce Thomas)

FIGURE 7. O. hoparatea. (photo: Marieke Lettink)