Varanus indicus species-complex

Varanus indicus species-complex

Mission Purpose

The Varanus indicus species-complex has undergone a dramatic taxonomical upheaval in the past couple of decades. What was once considered a single variable species spread over a vast swath of territory today is composed of thirteen (so far!) recognized species. Numerous other forms await taxonomic review and even more are out there to be discovered. Many of these mystery animals originate from the pet trade. Thus, they almost always come without reliable locality data and so the mystery deepens. These specimens represent important new discoveries but too often they have a picture posted somewhere, soon to be forgotten or removed and that is that.

The purpose of this website is to act as a photographic database of the numerous species, color forms, and mystery specimens. While detailed phylogenetic studies are needed to truly resolve matters, hopefully a detailed collection of the different phenotypes will assist.

The website exists as a photobank for arguably the most variable group of the monitor lizards. Range data and some basic habitat/habit information is also provided, though the emphasis lies on producing a visual library. Additional information on these and other Varanid lizards can be found in the 'Links' section. Besides the available photos, a basic physical description of the species in question is also provided. Again, it must be noted that this group of animals displays enormous phenotypic variety. Many variations are to be found which may represent either minor deviations from the normal or, potentially, completely new taxa. The given information is meant to describe the typical form, and as such has mostly been taken from the species' original description. The descriptions are focused on color and pattern; diagnostic features which vary considerably even to the level of individuals (such as scalation) or which are of little practical use outside of the lab (genital morphology) are omitted.

Range

The mangrove monitors represent one of the most geographically widespread groups of the genus Varanus. Members are found as far east as the Talaud Archipelago, throughout the Moluccas (possibly occuring on Sulawesi - Böhme 2003 - though this is under dispute), Timor (Böhme et al 1994), New Guinea and surrounding islands, the Bismarck Archipelago, parts of coastal northern Australia, east to the Solomon Islands, and northern through parts of Micronesia (where, in many areas, they are belived to have been introduced; see Cota 2008). Currently, the Moluccas appear to be the epicenter of indicus-complex diversity with eight out of thirteen recognized species known to occur here. The presence of two others is suspected but not yet confirmed and a number of forms which await scientific description are from or rumored to be from this region. Some islands (notably Halmahera) are home to several different species, offering an interesting look into niche partitioning (see Weijola 2010).

* A quick note about locality data. Locality data in indicus-complex animals is gathered through a few principle ways. Museum specimens are a reliable source as these are (usually) catalogued with data as to when and where the specimen was collected. Unfortunately, museum specimens for many species are poor at best. Field photographs are another good reference as their ability to be published in print or online makes them readily available. However, most such available photos represent a few of the better known species as, so far, many other forms remain largely unstudied in the wild. One major (and increasing) source of indicus-complex specimens is the international pet trade and new forms appear on the market on a fairly regular basis. However, locality data on these animals is almost always either absent or suspect. Typically, by the time these animals reach their final dealer they have changed hands through numerous middlemen who mix them with other specimens from other areas and have little reason to make a note of their exact origins. In the case of new and particularly sought-after forms, it is often to the initial collector's economic benefit to keep the source of these animals secret. As a result of all this, locality data on pet trade specimens must almost always be taken with a grain of salt and usually consists of rumors which have circulated one way or another or pure guesswork. When locality data on pet trade animals is provided to me, I include it on this site for reference. However, such data must be considered within the context described above.

General Information About the Varanus indicus Species-Complex

While there is much difference between different indicus-complex species in regards to habits, diet, etc, the majority of forms appear to be semi-arboreal/terrestrial with the animals sheltering in trees but doing the majority of their foraging on ground level. Many species are also quite aquatic, though to what extent varies. Like most other Varanids, mangrove monitors are opportunistic feeders taking a wide variety of mostly small prey such as arthropods and other invertebrates (both terrestrial and aquatic), fish, and to a lesser extent vertebrates such as other lizards, rodents, or birds.

Diagnostic Features

The Varanus indicus species-complex, together with the tree monitors (Varanus prasinus species-complex), form the subgenus Euprepiosaurus (Fitzinger 1843). Euprepiosaurus was distinguished from other members of Varanus on the basis on genital morphology (Böhme 1988). Mangrove monitors are further characterized by a laterally compressed tail (in all species except Varanus juxtindicus), enlarged supraocular scales, and slender digits. Most species possess some degree of enlargement above the nasal area as well.

Differentiating between the different species of the indicus-complex is made difficult by the great variation exhibited by this group: one region may harbor a number of distinct forms, one particular phenotype may be found in varying locales, and what may be believed to represent a single form may show numerous slight (or not so slight) variations among the many islands it inhabits. The following features are most commonly employed in determining taxonomy:

  • Color and pattern - This represents the most basic and straightfoward way of distinguishing different forms and has historically been the basis of determining taxonomy. However, color and pattern fall short on a number of points. For one, as already extensively mentioned, some groups of organisms show great variation between different populations, as well as among individuals. Further differences in pattern may be ontogenetic; members of the mangrove monitor-complex are known to go through considerable changes in appearance as they age (see Wesiak & Koch 2009 for one such example). On the other hand, some populations which appear identical may be genetically distinct and reproductively isolated. In mangrove monitors, color and pattern may be helpful tools but should not be relied upon for identification purposed. Currently, the known variety of this species-complex is so great and the taxonomical situation so confused that many specimens simply cannot be assigned to any currently recognized taxa on the basis of appearance. One feature of coloration which is usually taxonomically constant is the presence or absence of blue pigmentation on the tail. While most disctinctive in Varanus doreanus, other species also exhibit some degree of blue color. In the species that do, it tends to be seen among nearly all specimens (An exception is Varanus jobiensis whose normal form possesses blue pigmentation while several color phases lack it. However, it is likely that jobiensis represents a complex of several taxa).
  • Tongue color - Tongue color appears to be fairly distinct among different species and is usually provided in taxon descriptions. It is believed that in areas in which more than one indicus-complex species occurs, it may serve as a means for individuals to distinguish their species from others (Sprackland 1995). Most indicus-complex species possess tongue which are either dark purple or pink (often with a dark tip) in color. Others include whitish (Varanus doreanus) and bright red (Varanus jobiensis). Some specimens are known whose tongue color varies from the norm, though whether these simply represent aberrant specimens or not is unknown.
  • Genital morphology - Genital morphology is an important tool in determining taxonomy in reptiles as differences in the structure of the organs are fairly constant among individuals. Thus, different specimens which appear very similar superficially but differ in this regard have in the past been reclassified as distinct. Likewise, similarities can indicate evolutionary relationships between taxa. Unfortunately, the simple nature of genital manipulation and examination does not allow this method to be of use in the field or among private keepers.
  • Genetics - Genetics has been used more and more in recent years in determining evolutionary relationships among Varanus (see Ast 2001; Fitch et al 2006 for example). Due to the previous discussed superficial variation among members of the indicus-complex, the taxonomy of this group is unlikely to be settled until extensive comparisons can be done among specimens. Unfortunately, the great geographical extent in which these animals occur along with the fact that most specimens represent pet-trade animals whose origins are not known would make this an enormous undertaking.
  • Mangrove Monitors in Captivity

    Members of the Varanus indicus species-complex have been available in captivity for decades. For much of this time, the species-complex was only known to consist of a single variable species. Even after taxonomic changes began to be made in the mid 1990s, the rapid and continuing pace of these changes were not always caught up with by dealers and even today the ‘mangrove monitors’ which turn up in the pet trade are a grab-bag of different species and variations. Given the continued confusion surrounding the taxonomy of this group, it is often impossible to place a given specimen under a particular species name with absolute certainty. In addition, there are many imports turning up which vary so drastically from described taxa that they are almost certain to represent new species.

    As the purpose of this site is as a taxonomic reference, I have not posted information on the care of indicus-complex specimens, which can be found on other excellent sites (links coming soon!). However, I do wish to provide a disclaimer. Members of the indicus-complex have a couple features going for them which make them appealing for keepers. Many are stunningly beautiful in appearance. In addition, since nearly all are imported they are often cheaply available. This is very much unfortunate as nearly all of these animals make extremely poor captives. As a general rule, indicus-type monitors are flighty creatures which respond poorly to stress and handling. And of course, imported reptiles carry their own range of difficulties. Potential keepers should realize that under the best conditions you will be responsible for an animal which will remain unapproachable and which you may rarely even see. If you have had prior experience with keeping monitor lizards and appreciate this species-complex for what they are, good luck. Just please be aware of what you are getting into.

    Sources

    Ast, J. C. (2001): Mitochondrial DNA Evidence and Evolution in Varanoidea (Squamata). Cladistics 17 (3): 211-226. 

    Böhme, W. (1988): Zur Genitalmorphologie der Sauria: funktionelle und stammesgeschichtliche Aspekte. Bonner zoologische Monographien 27: 1-176. 

    Böhme, W. (2003): Checklist of the living monitor lizards of the world (family Varanidae). Zoologische Verhandelingen, Leiden 341: 3-43. 

    Böhme, W.; Horn, H. & T. Ziegler (1994): On the taxonomy of the Pacific monitor lizards (Varanus indicus complex): Resurrection of Varanus doreanus (A.B. MEYER, 1874) and description of a new subspecies. Salamandra 30 (2): 119-142.

    Cota, M. (2008): Varanus indicus and its presence on the Mariana Islands: natural geographic distribution vs. introduction. Biawak 2 (1): 18-27. (http://www.varanidae.org/Vol_2_No_1.pdf)

    Fitch, A. J.; Goodman, A. E. & S. C. Donnellan (2006): A molecular phylogeny of the Australian monitor lizards (Squamata: Varanidae) inferred from mitochondrial DNA sequences. Australian Journal of Zoology 54: 253-269.

    Sprackland, R. G. (1995): Evolution, systematics and variation of Pacific mangrove monitors and their kin. Unpublished Ph. D. Thesis, University College London.

    Weijola, V. S. A. (2010): Geographical distribution and habitat use of monitor lizards of the north Moluccas. Biawak 4 (1): 7-23. (http://www.varanidae.org/Vol4_No1.pdf)

    Wesiak, K. & A. Koch (2009): Successful husbandry and first breeding of Varanus juxtindicus Böhme et al, 2002, with remarks on the development of juveniles of this "rarely-kept" endemic Solomon monitor species. Biawak 3 (4): 106-121. (http://www.varanidae.org/Vol3_No4.pdf)

    Contact Info

    Do you have photos or information which might be published on this site? Send it to:

     indicuscomplex@yahoo.com