Wednesday, February 24, 2016

[Herpetology • 2016] Varanus semotus • A New Blue-tailed Monitor Lizard (Squamata, Varanus) of the Varanus indicus group from Mussau Island, Papua New Guinea

Varanus semotus 
Weijola, Donnellan & Lindqvist, 2016

an adult in its habitat at the outskirts of Nai (photos by VW), and a juvenile (photo by Quetzal Dwyer).

We describe a new species of Varanus from Mussau Island, north-east of New Guinea. The new species is a member of the Varanus indicus species group and is distinguished from all other members by both morphological and molecular genetic characters. It is the third species of Varanus reported from the Bismarck Archipelago and the first record of a yellow tongued member of the Varanus indicus species group from a remote oceanic island. The herpetofauna of Mussau Island has not been well studied but the discovery of this new species is in accordance with recent findings indicating that the island may harbor several unknown endemic vertebrates. The distribution of the closely related Varanus finschi is also discussed in the light of recent fieldwork and a review of old records.

Keywords: Melanesia, Bismarck Archipelago, St. Matthias islands, Varanidae, Varanus doreanus, Varanus finschi, Varanus yuwonoi, mitochondrial phylogeny, biogeography, taxonomy

Figure 3. A–C Images of live Varanus semotus at Nai on Mussau Island.
A an adult in its habitat at the outskirts of Nai B an adult basking on the trunk of a palm tree (photos by VW), and C a juvenile (photo by Quetzal Dwyer).

Etymology: The specific epithet semotus is Latin for distant or remote and refers to the isolated occurrence on Mussau, separated by several hundred kilometers from its closest relatives. The term is employed as a masculine adjective.

Diagnosis: Varanus semotus sp. n. is distinguished from all other species of Varanus by a combination of the following characters. (1) Tongue white/pinkish to pale yellow (white in preservative) occasionally with small patches of dark pigmentation, the yellow pigment concentrated along the mid-dorsal line and the dorsal surface of the tines (Fig. 2). (2) Gular region marbled in black and cream-white. (3) The tail of adult individuals is indistinctly banded on the distal half, with a varying degree of turquoise to bluish pigmentation on the distal 2/3. (4) Juveniles are black with white spots on the head, yellow and orange spots on the dorsum, and have well defined cream colored to pale greenish tail bands (Fig. 3C). (5) The number of dorsal scales, XY, ranges from 149 to 153. (6) The number of midbody scale rows, S, ranges from 152 to 161. (7) The dorsum is black with single- and clustered groups of dispersed yellow/orange scales. (8) There are several complete rows of paryphasmata across the asulcal side of the hemipenis below the lobes. (9) Geographical distribution restricted to Mussau Island.

Distribution: Varanus semotus is known so far only from Mussau, an island of 414 in the northern Bismarck Sea (Fig. 5). According to some of the locals on Mussau, monitors are absent from Emirau, the second largest island of the St. Matthias group, but this needs confirmation from fieldwork. It is also unknown whether this species occurs on the other two nearby islands Emananus and Eloaua.

Natural history: A total of 16 observations were made during fieldwork on Mussau, all of them along the coast near the village of Nai at the SE corner of the island. Searches in the secondary growth forest of the interior of the island and in the mangrove forests near Palakau did not produce any observations. The relatively dry coastal vegetation near Nai comprises a mixture of coconut palms, pandanus and other trees and shrubs able to persist in the karst, limestone and salt spray affected area (Fig. 6). In this vegetation type monitors appeared to be relatively common. Just south of the village there is a freshwater spring with a small area of Sago palms which was also a popular site for monitors. The lizards were usually spotted either as they were foraging on the ground and quickly fled up in trees, or while they were basking on the trunks of palms or other trees. The specimens collected as vouchers were noosed from trees with a long pole. As is typical of the closely related V. doreanus, V. finschi and V. yuwonoi the specimens were exceedingly aggressive and inclined to bite when captured and handled. Stomach content analysis of the three ZMUT specimens revealed a total of five reptile eggs (3,2,0) and one small skink. All stomachs contained the remains of crabs. Philipp et al. (2007) recorded a bird as the stomach content of ZMUC 4272.

Conservation. The field observations indicate that V. semotus doesn’t occur, or possibly only at low densities, in the highly degraded secondary forest/bush of large parts of the interior of the island. It is likely that the species occurred throughout Mussau prior to the large scale logging activities of the past three decades (Venter and Arihafa 2015). Thus the species is now mostly restricted to the coastal strip of a relatively small isolated island. Possible threats to the future survival of this species would be the introduction of cane toads which were widely established in the PNG islands during WW2 (Zug et al. 1975). According to unconfirmed accounts by locals they already occur on Emirau Island which also according to local inhabitants on Mussau lack monitor lizards. Varanus semotus is the only large-sized terrestrial generalist predator and scavenger on the island, and may well fill an important ecological function, making it of particular conservation concern. The new species is unusual inasmuch as it fills a role normally occupied by Mangrove monitors on isolated Pacific islands and it can well be considered a biogeographical oddity.

 Valter Weijola, Stephen Donnellan and Christer Lindqvist. 2016. A New Blue-tailed Monitor Lizard (Reptilia, Squamata, Varanus) of the Varanus indicus group from Mussau Island, Papua New Guinea. ZooKeys. 568: 129-154. DOI:  10.3897/zookeys.568.6872