Two new species of monitor lizards (Squamata: Varanus) endemic to the Louisiade and Tanimbar Archipelagos with a key to the subgenus Euprepiosaurus

ABSTRACT We describe two new species of Varanus, one each endemic to the Louisiade and Tanimbar Archipelagos in Papua New Guinea and Indonesia, respectively. The new species belong to the subgenus Euprepiosaurus and, therein, to the widely distributed and relatively species-rich Varanus indicus group. They can be distinguished from all other recognised species by scalation, colour-pattern and genetic differences. The new species from Tanimbar is most closely related to V. indicus and V. melinus, from which it can be distinguished by its dark blue/grey tongue and higher middorsal and midventral scale counts. The new species from the Louisiades can be distinguished from its phylogenetically and geographically nearest relative, V. chlorostigma, by the presence of dorsal crossbands, the mostly pink tongue mottled with grey, and higher midbody scale count. The Louisiades constitute the easternmost archipelago of Milne Bay Province in eastern Papua New Guinea, and they host a diverse herpetofauna with a high degree of endemism; Varanus louisiadensis sp. nov. increases the known number of herpetofaunal endemics in that archipelago to 60. The Tanimbar Islands are situated in the southern part of Maluku Province (Moluccas), Indonesia, and are a minor centre of vertebrate endemism; Varanus tanimbar sp. nov. increases the number of known herpetofaunal endemics there to six. http://www.zoobank.org/urn:lsid:zoobank.org:pub:E06BDE2A-0B24-4CB5-B46E-6B93476CC3EB


Introduction
Lizards of the genus Varanus Merrem, 1820 occurring in the south-western Pacific are largely confined to a clade comprising the monophyletic subgenus Hapturosaurus Bucklitsch, Böhme and Koch, 2016 plus three species groups within its monophyletic sister group, the subgenus Euprepiosaurus Fitzinger, 1843 (Ziegler et al. 2007;Weijola et al. 2019). Hapturosaurus consists of eight species found across New Guinea, several of its surrounding islands, and the northern tip of Australia. Within Euprepiosaurus, the V. jobiensis Ahl, 1932 group consists of a single nominal species restricted to New Guinea and the land-bridge island of Waigeo; the V. doreanus Meyer, 1874 group consists of four species ranging from New Britain to Mussau, New Guinea, Aru, Waigeo, Biak and Halmahera; and the V. indicus Daudin, 1802 group comprises 11 nominal species widely ranging from the Moluccas to the Solomon Islands and from northern Australia through western Micronesia (Weijola et al. 2019(Weijola et al. , 2020. The exact phylogenetic relations of Varanus caerulivirens Ziegler, Böhme and Philipp, 1999 and V. zugorum Böhme and Ziegler, 2005 also within the subgenus Euprepiosaurus -are unknown, but neither appears to fit clearly into any of these three species groups. Phylogenetic results obtained using molecular data indicate that each of these clades requires further taxonomic investigation, but the V. indicus group is of greatest interest because it has the broadest range (Figure 1), greatest number of lineages, and most recent divergence times, having radiated across this vast region only since the Pleistocene (0.9-1.9 Mya). Within the Varanus indicus group, the molecular phylogeny published by Weijola et al. (2019) supported the status of the four then-recognised species for which genetic material was available but also identified several other distinct lineages as candidate species, although these have historically been subsumed under the name V. indicus. Subsequently, the taxonomic status of the Micronesian populations was revised, resulting in the recognition of V. bennetti Weijola, Vahtera, Koch, Schmitz andKraus, 2020 andV. tsukamotoi Kishida, 1929 from Palau, the Federated States of Micronesia, and the Mariana Islands (Weijola et al. 2020). Böhme et al. (2019) described V. colei Böhme, Jacobs, Koppetsch and Schmitz, 2019 from the Kei Islands based mainly on morphological characters.
Here we continue to refine the taxonomy of Euprepiosaurus by describing two additional insular species of the V. indicus group (senso Weijola et al. 2019), of which one is endemic to the Louisiade Archipelago in easternmost Papua New Guinea and the other is endemic to the Tanimbar Islands in Maluku Province, Indonesia. Molecular data (Weijola et al. 2019) indicate that both species represent independent evolutionary lineages within the V. indicus group, and each is reliably distinguished from related species by external morphology. We also provide an updated key to the species belonging to the subgenus Euprepiosaurus, which has grown from 11 to 20 recognised species since the last key to the subgenus was published (Ziegler et al. 2007).
In this paper we follow the nomenclatural use for V. indicus Daudin, 1822, V. cerambonensis Ziegler, 1999, andV. chlorostigma Gray, 1831 proposed for the International Commission on Zoological Nomenclature (ICZN) in Case 3676 (Weijola 2015) and accepted in ICZN Opinion 2451 (ICZN 2020). Accordingly, V. cerambonensis is treated as a junior synonym of V. indicus and the name V. chlorostigma Gray, 1831 is used as the valid name for the species on New Guinea, many of its satellite islands, and parts of northern Australia (V. indicus sensu Philipp et al. 1999), while V. indicus is the valid name for the taxon endemic to Ambon, Seram, Buru, Saparua, Haruku and Banda islands. Because V. indicus is the oldest name for any species in this clade, we continue to refer to it as the 'Varanus indicus group'.

Morphology
The linear discriminant analysis retrieved a group structure that distinguished among several of the included species and candidate species (Figure 2). The candidate species from Tanimbar shows partial overlap in multivariate space with the candidate species  (Weijola et al. 2019). Axes 1 and 2 account for almost 75% of morphometric variance in the samples; counts N, P, and T provided the greatest discrimination on Axis 1 and counts Q and XY on Axis 2 (Table 2).

Taxonomy
The morphological data presented here and the previously published molecular phylogenetic analyses (Weijola et al. 2019(Weijola et al. , 2020 both indicate that the Varanus populations

Etymology
The specific epithet refers to the Louisiade Archipelago of Milne Bay Province, Papua New Guinea, where this species is endemic.

Diagnosis
Varanus louisiadensis sp. nov. is a member of the subgenus Euprepiosaurus, which is defined by having the unique combination of an asymmetric sperm groove on the hemipenis and a laterally compressed tail (Ziegler et al. 2007). Molecular phylogenetic analyses place it within the V. indicus species group defined by the unilateral paryphasmata ornamentation of the hemipenis and lack of blue pigmentation on the tail (Ziegler et al. 2007;Weijola et al. 2019). It can be distinguished from all other species of Euprepiosaurus by its unique combination of: (1) dorsum black with more-or-less well-defined crossbands composed of yellow ocelli and/or dots, better defined in juveniles and subadults than adults; (2) tail black with distinct yellow bands, better defined in juveniles and subadults than adults; (3) tongue tines and a variable section of the mid-dorsal tongue surface dark grey, the remainder being pink; (4) pink-orange pigmentation usually present on cheeks and sides of neck; (5)   Description of the holotype. Well-preserved juvenile with a small incision on left thigh from where tissue was removed. Dorsal ground colour of body, tail, head and limbs black, covered by distinct crossbands of yellow rosettes and dots. Habitus slender; total length 585 mm (SVL = 240 mm, F = 345 mm); tail 1.44 times as long as body, 36.3 times as long as high (9.5 mm) at midlength, round at base, becoming laterally compressed distally, and with mid-dorsal ridge two scales wide starting at about 30 mm from base. Thirteen discernible cream-coloured crossbands on distal ¾ of the tail. Venter cream yellow, marmorated with brown, with incomplete crossbands between hind legs and gular fold that are one scale row wide. Throat cream with scattered brown scales laterally. Ventral surfaces of limbs cream with narrow, pale-brown bands and dots. Under tail cream with interspersed brown scales at base of tail. Dorsal surfaces of limbs black with yellow dots, stripes, and ocelli composed of about 1-8 scales.
Head 1.82 times as long as wide, black with yellow dots and short stripes and with bright-yellow parietal scale. Well-defined temporal bands or postocular stripes lacking on both sides of head. Labial scales white at snout but each from below nostril to labial commissure with a brown dot. Nostrils oval, situated slightly nearer to snout than eye. Nasal capsules expanded, with shallow sagittal groove on rostrum.
Nuchal scales irregular in shape on anterior part of the neck, round on mid-neck, smaller and elongate on lower neck, all surrounded by granules. Dorsal scales somewhat irregular in size, elongate, keeled, each surrounded by few granules, most with single pit. Lateral caudal scales regular in size and shape, rectangular, flattened, usually with single posterior pit. Mid-ventral caudal scales twice as wide as mid-dorsal caudal scales, elongate, with sharp keel. Mid-ventral scales rectangular, flat, posterior margin rounded and bordered by row of granules. Scales on chest irregular in size, round to polygonal, each surrounded by few granules. Gular scales roundish to polygonal, each surrounded by granules. Mental scales elongate, rectangular to polygonal.
Infrafemorals and infratibials round, each surrounded by row of granules along lateral and posterior margins. Infracarpals and infratarsals round and highly domed, with brown traction pads on most scales. Subdigital scales domed, of irregular size and shape. Fourth toe with row of 11 (R) and 12 (L) enlarged scales along outer margin; third toe with four slightly enlarged scales along outer margin. Claws dark brown, sharp, and recurved. Occipital scales flattened, relatively small, irregularly polygonal. Supraocular scales 8 (R) and 7 (L), enlarged, irregular in shape and size, each densely covered with pits. Scales of forehead and rostrum polygonal, flattened, larger than occipital scales. Supralabials pentagonal or rectangular, covered with pits. Infralabials of irregular size, pentagonal or polygonal. Tines of tongue blue, its trunk pink, except for thin, blue median line on both dorsal and ventral sides.  Table 3.

Variation and colouration in life.
Variation is mostly seen in the dorsal crossbands which can be composed of either spots and ocelli or spots only (Figures 4-6). Judging from the material at hand these also tend to become less distinct as the animals age. The extent of grey pigmentation on the tongue varies considerably between individuals, varying from colouring only the tines to encompassing the whole dorso-distal half of the trunk.  Range. Varanus louisiadensis sp. nov. has been recorded from coastal and lowland areas on all three major islands of the Louisiade Archipelago: Misima, Sudest, and Rossel ( Figure  7). Considering the good dispersal abilities of monitors in the V. indicus group it can also be expected to occur on nearby smaller islands with suitable habitat, such as Paneati and Panatinane islands, but its presence on satellite islands of the Louisiade Archipelago has yet to be confirmed.

Remarks
The molecular phylogeny of Euprepiosaurus published by Weijola et al. (2019)

Etymology
The specific epithet tanimbar is a noun in apposition and refers to the Tanimbar Archipelago of Maluku, Indonesia, to which this species is endemic.

Diagnosis
Varanus tanimbar sp. nov. is a member of the subgenus Euprepiosaurus, which is defined by having the unique combination of an asymmetric sperm groove and laterally compressed tail (Ziegler et al. 2007). Molecular phylogenetic analyses place it within the V. indicus species group defined by the unilateral paryphasmata ornamentation of the hemipenis and lack of blue pigmentation on the tail (Ziegler et al. 2007;Weijola et al. 2019). It can be distinguished from all other species of Euprepiosaurus by its unique combination of: (1) dorsum black with more or less well-defined crossbands composed of lemon-yellow ocelli and/or dots; (2) tail black with distinct yellow bands; (3) dorsal aspect of tongue blue-grey; (4) temporal region typically ornamented with a dark temporal band and a lemon-yellow postocular stripe; (5)   pattern of yellow ocelli arrayed more or less into crossbands (vs more irregularly scattered yellow spots in V. rainerguentheri) and the higher mid-body (S) scale counts (145-161 in V. tanimbar vs 120-139 in V. rainerguentheri).    Description of the holotype. Juvenile, abdomen opened with both single vertical and longitudinal slits; basal 1/3 of tail with longitudinal cut along ventral side. Habitus slender, total length 500 mm, SVL 200 mm, tail length 300 mm; head elongate. Ground colouration of dorsum, neck and head dark brown to black; densely scattered with pale grey/blue (yellow in life) scales; small blotches and rings/rosettes indistinctly arranged as crossbands over dorsum. These rings and spots are composed of grey/blue (yellow in life) scales; the skin surrounding the scales is grey/black. Tail black, banded on distal 2/3 of length by 17 indistinct bands, each 5-7 scale rows wide. Tail 1.5 times as long as body, relatively elongate (36.14 times as long as high at midlength). Dorsal keel formed by 1-4 enlarged mid-dorsal caudal scales starting at ~35 mm posterior to tail base. Tail round at base, becoming triangular where keel is formed and increasingly laterally compressed to around midlength. Ventral ground colour pale cream, intersected by numerous (23) grey crossbands between cloaca and gular fold.
Ventral sides of limbs cream coloured and intersected by mosaic of narrow grey bands. Pale cream stripe 10-12 mm (~18 scale rows) wide between snout and gular fold; throat rapidly turning marmorated lateral to this. Tail cream ventrally, densely covered by indistinct grey crossbands most clearly visible on basal and distal 1/3 of tail. Limbs black dorsally with white/grey (yellow in life) spots composed of about 1-7 scales. Head 1.96 times as long as wide, dorsal aspect black with small amount of white on most scales, yellow parietal scale, dark temporal band ~5 scales wide, and white postocular stripe ~2 scales wide. Supralabials and infralabials paler than rostrum and dorsal aspect of head. Nostrils slightly elongate, pointed at anterior corner, closer to snout than to eye. Nasal capsules slightly expanded, with shallow sagittal groove on rostrum.
Nuchal scales of irregular shape on upper neck, round at mid-neck, and increasingly elongate towards shoulders; nuchals domed, with one to several scale pits, surrounded by one or two rows of granules. Dorsal scales oval, slightly irregular in size, domed or keeled (towards abdominal region), most with single pit posteriorly and surrounded by single row of granules. Lateral caudal scales rectangular, elongate, with a single pit centrally or posteriorly. Ventral caudal scales rectangular, elongate, strongly keeled, twice length of mid-dorsal caudals, occurring in row of 10 at midlength of tail. Ventral scales of pubic region polygonal to round, bordered posteriorly by row of granules. Abdominal scales rectangular with rounded corners, bordered posteriorly by row of granules. Ventral scales become increasingly less elongate and round towards chest and finally quadrate or polygonal and irregular in shape near gular fold; ventrals polished, often equipped with single pit and with few granules posteriorly. Gular scales rounded with few granules along posterior edge but become oval to rectangular and elongate towards mental region; mental scales larger laterally, rectangular or polygonal and densely covered in pits. Infrafemorals and infratibials round or polygonal, often with a few granules along posterior margin. Infracarpals and infratarsals round, of irregular size, highly domed. Subdigital scales irregular in size and shape, highly domed to almost flat. Twelve rows of enlarged scales along outer margin of fourth toe; four slightly enlarged scales along outer margin of third toe. Claws brown/translucent, sharp, recurved.
Occipital scales relatively small, irregular, polygonal. Five enlarged, irregularly shaped supraocular scales, elongate rectangular to pentagonal, densely covered with pits. Scales on forehead and rostrum larger than occipital scales, polygonal, flattened. Supralabials rectangular or pentagonal, covered with pits. Infralabials of irregular size, triangular or polygonal. Tines and dorsal aspect of distal half of tongue grey. Lateral sides of tongue white with only a small amount of grey pigment; distal half of ventral aspect pale blue with a grey central groove.  Table 3.

Variation and colouration in life.
The paratypes are similar to the holotype although there is some variation in the amount of dark pigmentation on the gular region, venter and ventral surfaces of limbs (Figures 8,9). While most individuals have a well-defined yellow temporal band, this was absent in one of seven individuals seen by us (Figure 12). In life, dorsal ground colour black; throat, dorsal spots, and ocelli greenish lemon-yellow (Figures 8-12). Tongue pink basally with grey blue on tines and dorsodistal half.

Range.
Varanus tanimbar sp. nov. is known from Yamdena and Selaru -the two largest islands in the Tanimbar Archipelago. The species is also likely to occur on surrounding islands such as Larat, Fordate, Wotap, Wuliaru, Selu and Sera, but its presence on those islands needs confirmation.

Natural history.
There are no specific details about the biology of this species, but it is likely similar in diet and habitat preferences to other closely related species of the V. indicus group, which are habitat generalists of mangroves, coastal, and lowland forests (Weijola and Sweet 2015). During a brief visit to Yamdena in 2009, VW found the species being hunted for food by local residents, and this might well suppress populations in the vicinity of human settlements.

Remarks
Varanus tanimbar sp. nov. formed a well-supported clade together with the Moluccan species V. indicus and V. melinus in the BEAST analysis based on the 16S and ND4 markers used by Weijola et al. (2019). Within this Moluccan clade, V. tanimbar sp. nov. formed a basal sister lineage to the closely related V. indicus and V. melinus. ND4 pairwise distances between V. tanimbar sp. nov. and these two species are 3.4% and 3.9%, respectively, and 2.3% between V. indicus and V. melinus (Weijola et al. 2019).

Discussion
The molecular phylogeny of Weijola et al. (2019) identified four named species as well as eight candidate species within the Varanus indicus group, with the candidate species each having a similar degree of genetic divergence to the already recognised species, hence pointing to the need for further partitioning of this species complex. Beyond mere molecular distinctiveness among these widely scattered insular populations, several also had consistent morphological differences that were immediately obvious in the field. Among the eight candidate species, two from Micronesia were geographically distinct and treated in a separate paper that resurrected the name V. tsukamotoi for the species in the Mariana Islands and described V. bennetti from Palau, Yap, and Sarigan Island (Weijola et al. 2020). The remaining six lineages are all from Melanesia (n = 5) and the Moluccas (n = 1), and herein we have treated two of those. The last four lineagesfrom the Solomon Islands and Admiralty Islands -are more difficult to diagnose, and we defer taxonomic action on those until more detailed molecular phylogenetic and morphological studies have been completed. Many of the islands in the Solomons also require further sampling to obtain a complete understanding of the species diversity and biogeographical patterns of that region.
The biogeographic history of the Varanus indicus group remains poorly settled at present. Weijola et al. (2019) noted that the most divergent lineages in that group were on islands peripheral to New Guinea, with the more recently derived V. chlorostigma occuring on New Guinea and nearby islands. They interpreted that pattern as consistent with the taxon cycle of island species turnover (Wilson 1961;Ricklefs and Bermingham 2002), though noting that it was only a preliminary hypothesis, given the data at hand. This was because the phylogeny presented by them was based on only two mitochondrial genes, and a more robust resolution of relationships based on nuclear markers is to be desired. Nonetheless, using their phylogeny as the best information currently available, we note that V. louisiadensis sp. nov. clustered in their tree with V. chlorostigma from western Melanesia and Australia, that V. tanimbar sp. nov. was a member of a clade of three southern Moluccan species, and that those Moluccan species were sister to a clade of populations from eastern Melanesia. Thus, V. louisiadensis sp. nov. and V. tanimbar sp. nov. have evolutionary and biogeographic origins that are distinctly independent of each other, occupying archipelagos isolated on the south-eastern and south-western peripheries of the distribution of the Varanus indicus group, respectively, yet each is most closely related to geographically proximate congeners.
For most biota the islands have not been well surveyed, so rates of endemism are likely to eventually prove higher than this. The Tanimbar Islands were formed from the collision of the oceanic Banda Arc with the Australian Plate, with the main phase of deformation occurring during the Pliocene (Charlton et al. 1991). This archipelago is bounded all around by deep water -including troughs to the east and west -so it has never been connected to other land masses. Consequently, the ancestors of species endemic to those islands arrived via trans-marine dispersal. Varanus tanimbar sp. nov. is estimated to have diverged from its closest relatives V. indicus and V. melinus approximately 900,000 years ago (Weijola et al. 2019), at a time well into the deformation creating the Tanimbar Islands.
Varanus louisiadensis sp. nov. occupies an archipelago of far greater importance for endemic biota, holding at least 221 endemic species of reptiles, amphibians, birds, land snails, heteropterans, odonata and plants (Polhemus and Allen 2007;Johns et al. 2009;Polhemus 2011;Pratt and Beehler 2015;Kraus 2021;J. Slapcinsky unpubl. data), the only taxa yet surveyed there. The Louisiade Islands comprise the three major islands of Misima, Sudest and Rossel, along with several smaller satellite islands. Only the major islands have been surveyed for reptiles and amphibians, though occasional specimens from the small islands have made their way into museum collections. The Louisiade Islands contain 59 endemic species of reptiles and amphibians, with Misima having 12, Sudest 20, and Rossel 20, and seven species being shared between Sudest and Rossel (Kraus 2021). Several of those 59 species remained to be described, and V. louisiadensis sp. nov. was one of them. It is the only endemic reptile or amphibian from this archipelago to be found across all three main islands, which may reflect the talent for trans-marine dispersal found in many Varanus species.
The Louisiade Islands were formerly connected to New Guinea as the outlying portion of the Owen Stanley Range, which forms the mountainous spine of the Papuan Peninsula. These islands became isolated from New Guinea in the past 6 million years as the opening of the Woodlark Rift led to crustal relaxation and submergence beneath sea level of the Pocklington Rise, the intervening land that connects the Louisiade Islands to the remainder of the Owen Stanleys (Taylor et al. 1999;Miller et al. 2012). The exact time at which the Pocklington Rise became totally submerged is unknown to us, but the molecular tree provided by Weijola et al. (2019) suggests that V. louisiadensis sp. nov. became isolated from V. chlorostigma approximately 900,000 years ago. Whether that isolation reflected loss of the land connection or trans-marine dispersal remains unknown, however.
Since the key and identification guides of Ziegler et al. (2007), Koch et al. (2013) and Auliya and Koch (2020) were published, five additional species of Euprepiosaurus have been described (V. semotus, V. colei, V. bennetti, V. louisiadensis and V. tanimbar;Weijola et al. 2016;Böhme et al. 2019;Weijola et al. 2020; this study), three species have been resurrected from synonymy (V. chlorostigma, V. douarrha and V. tsukamotoi;Weijola 2015;Weijola et al. 2017Weijola et al. , 2020ICZN 2020), and V. cerambonensis has been designated as a junior synonym of V. indicus (Weijola 2015;ICZN 2020). Hence, we find it advisable to provide updated identification charts and a diagnostic key to all currently recognised members of this subgenus. Species identification is generally uncomplicated for specimens with known geographical origin. Wherever two or more species of Euprepiosaurus occur in sympatry they belong to different species groups and are easily distinguished from each other based on characteristics such as colour pattern and scale counts. Below we provide two tables with scale-count characters (Table 4) and colouration and range (Table 5).

A dichotomous key to the subgenus Euprepiosaurus
Most monitors go through some form of ontogenetic colour change from hatchling to maturity, making it difficult to produce a key that accommodates all life stages. The colour-pattern characteristics used in the key provided below are adapted to animals that have passed the juvenile stage. It should also be taken into account that some characters -in particular yellow or white pigmentation of the tongue -are often lost in preserved specimens. For comparative purposes, photographs of most of these species in life may be found in Auliya and Koch (2020).