Varanus tsukamotoi Kishida, 1929

Weijola, Valter, Vahtera, Varpu, Koch, André, Schmitz, Andreas & Kraus, Fred, 2020, Taxonomy of Micronesian monitors (Reptilia: Squamata: Varanus): endemic status of new species argues for caution in pursuing eradication plans, Royal Society Open Science 7 (5), pp. 1-28 : 12-61

3.4. Varanus tsukamotoi Kishida, 1929 , figures 5–7

3.4.1. Neotype

Although Kishida designated a holotype (a young female collected on Saipan by Inenosuke Iwai), he did not provide a catalogue number, and the specimen in question is now considered lost, as seems to be the case with most of Kishida’ s collections [46,47]. To promote taxonomic stability, inasmuch as two Varanus species of the V. indicus Group inhabit the Mariana Islands, we designate USNM 576258 ( figure 5 a,b ) as neotype for this species. The specimen was collected by Ronald Crombie on 15 July 1999 in a scrubby forest at Makpi at the north end of Saipan Island in the Commonwealth of the Northern Marianas .

3.4.2. Additional specimens examined

Mariana Islands: Anatahan ( USNM 212496 ) ; Cocos Island ( USNM 494383 ) ; Guam ( AMNH 137204 , USNM 121793, 122462 –63, 122465, 122468, 121796, 216368, 216869, 323717, 494380–82, 494582, 507452, 515827–29, 521160) ; Pagan ( USNM 212489 , 212491–93 ) ; Rota ( AMNH 137202–03 , 139986–88 , USNM 122652 –53, 285037) ; Saipan ( SMF 30152–53 , USNM 212487–88 , 576257 , 576259 , ZMB 22645) ; Tinian ( USNM 308067 ) ; indefinite locality ( MNHN 1888 20) ; Marshall Islands: Enewetak Atoll , Japtan Island ( AMNH 78994 , USNM 124112–13 ) .

3.4.3. Diagnosis

Varanus tsukamotoi can be distinguished from all other members of the V. indicus group by its unique combination of: (i) dorsum black and covered with evenly distributed yellow scales, (ii) tongue dark blue/grey, (iii) yellow temporal stripe usually absent, (iv) low scale counts around the head (P: 31–40), tail base (Q: 54–74) and midbody (S: 101–126), and (v) usually prominent dark pigmentation in the gular region.

3.4.4. Comparisons with other members of Euprepiosaurus

Varanus tsukamotoi can be distinguished from V. caerulivirens , V. colei , V. doreanus , V. finschi , V. jobiensis , V. juxtindicus , V. melinus , V. obor , V. semotus and V. yuwonoi by having an entirely dark blue/grey tongue rather than (at least partly) pink or yellow tongue; from V. cerambonensis by the absence of a yellow temporal stripe, dorsal bands composed of yellow scales and lower midbody scale counts (S: 101–126 versus 131–150 in V. cerambonensis ); from V. douarrha by the absence of dorsal ocelli and lower midbody scale counts (S: 101–126 versus 129–153 in V. douarrha ); from V. indicus by its lower average scale counts around head and tail base (P: 31–40 (34.8) versus 36–47 (42) in V. indicus , Q: 54–74 (67) versus 60–99 (78.4) in V. indicus , S: 101–126 (113.5) versus 100–145 (124) in V. indicus ) and by having dark pigmentation on the throat (versus usually cream-coloured in V. indicus ); from V. lirungensis by the absence of dorsal cross-bands composed of yellow scales, dark pigmentation on the gular region (versus pink in V. lirungensis ) and by lower scale counts around head, tail base and midbody (P: 31– 40 versus 38–47 in V. lirungensis , Q: 54–74 versus 79–88 in V. lirungensis , S: 101–126 versus 134–151 in V. lirungensis ); and from V. rainerguentheri by the absence of a yellow temporal stripe, by the presence of dark pigmentation on the throat (versus a mostly light-coloured throat in V. rainerguentheri ), and by lower scale counts around tail base, midbody and along the venter (Q: 54–74 versus 76–82 in V. rainerguentheri , S: 101–126 versus 120–139 in V. rainerguentheri , T: 78–88 versus 90–94 in V. rainerguentheri ).

A subadult specimen of undetermined sex with total length of 800 mm (SVL: 315 mm, F: 485 mm). Specimen well preserved, without signs of degradation or loss of keratin layer. Tail 1.54 times SVL, 33.5 times length of midlength height, round at base, but at 40 mm posterior to cloaca becoming increasingly compressed laterally and gaining a double scale ridge dorsally. Dorsal ground colour of trunk and limbs, head and tail black. Yellow scales—scattered singly on the dorsum and in rows of up to seven on the flanks—decorate the dorsum and dorsal sides of limbs and neck. Distal half of tail more densely spotted with yellow scales than proximal, often accumulated in latitudinal and longitudinal rows of scales, but lacking distinct cross-bands. Ventral and subcaudal scales cream coloured or grey with dark brown upper margin; scales of upper chest and gular region a mixture of cream and grey scales, some partially covered by dark brown pigmentation, appearing grey to the naked eye. Scales of ventral surfaces of limbs cream coloured, interstitial skin pale brown. Palms and soles with dark-centred, domed traction scales. Subdigital scales dark black, more or less domed and arranged in triple rows. Eight basalmost scales of the inner side of the fourth toe enlarged. Claws dark brown, sharp and recurved.

Nostrils oval, slightly compressed vertically, pointed at the rear end, surrounded by seven and eight scales, respectively. Nasal capsules slightly expanded, with a shallow groove on the rostrum. Tongue and tines dark blue-grey on both dorsal and ventral surfaces. Teeth pointed and recurved.

Dorsal head scales dark brown, polygonal and irregular in shape and size; most partly pigmented in yellow, often along one or two of the scale margins. Supralabials pentagonal, rectangular or irregular, densely covered with pits. Four scale rows between mouth nostrils, eight scale rows between nostrils across the snout. Enlarged supraoculars five on left, four on right, supralabials 23 on each side, rostral enlarged, pentagonal. Occipital damaged, scarred. Temporals irregular in size and shape, with numerous pits.

Nuchals variable in size, round to slightly oval, relatively flattened, with four to five pits, bordered by row of enlarged granules along lower and sometimes lateral margins. Smaller granules cover interstitial skin. Dorsal scales slightly more domed than nuchals or with a blunt keel, most with a single pit at posterior end. Caudal scales small, elongate rectangular, with small median ridge and single pit.

Gulars cream or grey, enlarged, rectangular or irregular near snout, quickly decreasing in size posteriorly; small and square near eye; increasing in size towards gular fold; oval black anterior border along gular fold. Many gular scales with centre dark brown. Chest scales polygonal, irregular, cream or grey, some with black anterior margin. Chest scales square with rounded posterior corners, at ribcage becoming elongate, rectangular, with black along anterior margin and row of granules along posterior margin. Ventrals with single pit at the posterior end. Subcaudals rectangular, increasingly elongate and ridged posteriorly. On distal two-thirds of tail subcaudals cream with black anterior of as much as third of scale.

3.4.6. Scalation

S 111, XY 129, DOR 138, T 84, VEN 100, X 39, m 86, P 35, Q 63 and R 51.

3.4.7. Measurements

SVL 315 mm, F 485 mm, TL 800 mm, A 47.5 mm, B 26 mm, C 18 mm, G 13 mm, H 10.5 mm.

3.4.8. Molecular evidence

Varanus tsukamotoi is resolved as a well-supported lineage (JF 94, BS 93, syn 4) in both parsimony and likelihood-based phylogenies. Its closest evolutionary relatives are the Varanus species to be described below (1.5/0.3% difference in ND4/16S) and V. lirungensis (1.4/0.3% difference), but the evolutionary affinities among these three species remain unresolved.

3.4.9. Variation and coloration in life

The specimens examined (n = 43) were generally fairly uniform in appearance. However, specimens from Pagan in the Northern Marianas were noticeably darker in coloration than specimens from other parts of the Marianas, particularly in the gular and ventral regions. Only one specimen ( USNM 494380 ) had a light temporal stripe. Tail banding varies from weak to non-existent. Photographs of live animals [9,14] ( figures 6 and 7) show them to have a black ground colour with bright yellow spots, the parts of the throat that are white in preservative also appear to be yellow in life. The largest specimen examined by us had a total length of 120.5 cm. Dryden & Taylor [ 48] reported a maximum total length of 133 cm among 100 specimens collected on Guam. A maximum weight of 2.2 kg was reported by Dryden [ 49] among 84 animals killed on Guam.

3.4.10. Etymology

Kishida named this species in honour of Dr Iwasaburo Tsukamoto, who supported his expedition to the South Sea Islands, and proposed ‘ Saipan monitor’ and ‘Tsukamoto Ohtokage’ as the English and Japanese vernacular names. We suggest the common name ‘Mariana monitor’ as it more accurately describes the distribution of this species.

3.4.11. Distribution

We have examined specimens belonging to this species from Guam, Cocos Island, Saipan, Rota, Pagan, Tinian and Anatahan islands in the Mariana Islands, and from Japtan Island in the Marshall Islands ( figure 1 ). Specimens deposited in BPBM from Aguiguan Island in the Mariana Islands were not examined by us but presumably represent this species inasmuch as the nearby islands of Guam, Rota, Saipan and Tinian all have this species. For the population on Japtan Island, a human introduction appears most likely (Fosberg [ 24] cited in Dryden [ 49]). There is a single specimen (ZMUC R4266) allegedly collected in the Bonin Islands (Ogasawara Islands) by C.B. Clausen in 1912 and examined by Philipp [ 50] with scale count values matching those of V. tsukamotoi . This record has subsequently been cited in the literature for including the Bonin Islands within the range of V. indicus [51,52]. However, as the Ogasawara Islands have been well surveyed by Japanese herpetologists (N. Iwai and M. Toda 2019, personal communication), including as part of gaining recent status as a UNESCO world-heritage site, and as there are no other records of Varanus from there, we believe this specimen represents a case of mistaken provenance.

3.4.12. Ecology

Dryden [ 49] examined the stomach contents of 84 animals dissected on Guam. The prey items found (in order of frequency) were giant African snails ( Achatina sp.), miscellaneous arthropods (insects, insect larvae and millipedes), rats ( Rattus mindanensis and R. exulans ), shrews ( Suncus murinus ), hermit crabs, earthworms, slugs, bird eggs, skink (1) ( Emoia cyanurum ), gecko (1) ( Hemidactylus frenatus ), blind snake (1) ( Indotyphlops braminus ), and a skink egg. Specimens removed from Cocos Island foraged at the island’ s dump and frequently included chicken bones in their stomachs (FK, personal observation). Wikramanayake & Dryden [ 53] studied the reproductive biology of Varanus on Guam and considered males to be sexually mature at 320 mm and females at 275 mm SVL. Mature males averaged almost three times the mass of mature females. Reproduction appeared to be seasonal, with mating taking place during the early dry season (December–April) and eggs presumably hatching during the wet season (April–December).

Figures

Figure 1. Map of the Pacific region showing the distribution of Varanus tsukamotoi (white dots), V. bennetti sp. nov. (red dots), V. lirungensis (yellow dot) and V. rainerguentheri (green dot).

Figure 5. (a) Dorsolateral and ventral aspects of the neotype (USNM 576258) of Varanus tsukamotoi. (b) Lateral profile of the head of the neotype (USNM 576258) of Varanus tsukamotoi.