I remember the time when our varanid fauna was understood to be composed only of two species, Varanus olivaceus and V. salvator, along with three subspecies, V. s. marmoratus from Luzon, Mindoro, Palawan, and the Sulu Islands, V. s. nuchalis from the Visayas, and V. s. cumingi, from Mindanao. The supposedly widespread Varanus marmoratus (as Monitor marmoratus) was described by Georges Cuvier in 1829, but in 1942, Robert Mertens placed V. marmoratus as a subspecies of V. salvator. In 2007, Koch et al reinstated V. marmoratus as a distinct species with a disjunct range covering Luzon and its satellite islands of Catanduanes and Polillo; Mindoro; Palawan and the offshore islands of Balabac and the Calamianes; and the island groups of Tawi-Tawi and Jolo.
Much has changed beginning in 2010 when a clearer understanding of the species as a whole brought about the recognition of V. palawanensis, V. rasmusseni, and V. cumingi samarensis, resulting in V. marmoratus being confined only to Luzon and Mindoro. Drawing from inferences by Luke Welton et al in 2013 providing suspicion that V. marmoratus from southern Luzon and Mindoro might be distinct species, Luke Welton, Scott L. Travers, Rafe Brown, and Cameron Siler in 2014 took steps further and concluded that the populations from southern Luzon, and Mindoro and Semirara belong to distinct lineages, leading to the establishment of two taxa, V. dalubhasa and V. bangonorum, respectively. Despite their close resemblance to V. marmoratus, the two species were said to be genetically related to V. nuchalis and V. palawanensis, respectively.
From their 2014 paper, Welton et al distinguished V. dalubhasa from V. nuchalis mostly by differing scale counts, although it seems that overlaps render supposed differences uncertain at best. From my own observations, V. nuchalis is visually distinct on account of their more pointed snouts and heads which have varying amounts of white pigmentation.
Differentiating V. dalubhasa from V. marmoratus is much more ambiguous, although the authors stated and showed, through accompanying relevant photographs, that the gular (throat) region of V. dalubhasa is white and ornamented with irregularly-shaped spots that are very small anteriorly, but becoming more conspicuous along the lateral margins. In contrast, the throats of V. marmoratus, even though still also having a white base, are heavily obscured by dense speckles.
Furthermore, the dorsal markings of V. dalubhasa are faint at the shoulder and neck regions, while these are more conspicuous and sharply defined in V. marmoratus.
In my college years, I got used to seeing ‘V. salvator’ being offered in the illegal pet trade with bold markings consisting of yellow ocelli with intervening bands consisting of smaller yellow spots, and numerous yellow, irregularly dispersed spots above the shoulder and neck regions. Some examples of this species have the ocelli replaced by fine yellow speckles that appear randomly distributed throughout the back.
I cannot, however, discount the possibility that there are specimens of V. marmoratus with more conservative patterning approaching that of V. dalubhasa, such as the one illustrated in Brown et al (2012). It may also be possible that such animals belong to species still unrecognized to this day. For example, I have seen somewhat slender, almost plain black varanids with enlarged nuchal scales with a wide, yellow V-pattern below the neck region.
However, animals I encounter both in the wild and in the possession of bush meat hunters in the province of Laguna have more subdued dorsal markings (much to my puzzlement and disappointment) comprised of white or yellow ocelli with no intervening bands, and diffused spots above the shoulder and neck areas.
The recognition of cryptic species has become prevalent not just in zoology, but in botany as well. To illustrate, a cryptic species is derived from a particular ancestor but is still in its evolutionary path; therefore, the appearance may not be well distinguished from its ancestor. In such cases, a cryptic species is distinguished only mainly by its genetic make-up, with very little outward differences, if at all.
In 2000, I rescued animals caught by hunters and subsequently freed them, but these hunters, who were under the impression that I was keen on keeping these lizards as “pets”, were dismayed and appeared to once again resort to butchering these animals as liquor food (pulutan) instead of handing them to me only to be released back.
So, when I received another individual in 2001, which came from the town of Sta. Maria, I started keeping it on a long-term basis while releasing subsequent captured animals whose disappearances in my possession was cloaked under the pretext of them dying or being sent to friends.
This animal, remaining under my care until its death in 2014, had white patterning instead of the usual yellow, with obscure shoulder and nape markings, and a predominantly white throat with scant black spots. At that time, I still referred to the animal as V. marmoratus but of now the supposition that it is V. dalubhasa.
From the same time period, I had the opportunity to observe two V. nuchalis in captivity; this species, of course, is the putative nearest relative of V. dalubhasa. Upon first seeing the former species in the flesh, I immediately noticed the atypical nostril placement; compared with monitors I have seen from both Luzon and Mindoro, as well as the Mindanaoan V. cumingi, the nostrils are positioned close to the middle of the snout, further back from the snout tip as in the case of the other water monitor taxa. Indeed, the nostril placement reminds me of the unrelated Dumeril’s monitor (V. dumerilii) than it is to varanids from the V. salvator complex.
Behaviorally, V. nuchalis is a much more defensive species as compared to all the Laguna monitors I have kept, and in the several months that my observation on these two individuals have spanned, there was definitely no toning down of the said defensiveness. Their defensive repertoire includes the raising of the body by the stiffening of all four legs, accompanied by the expansion of the throat and a very audible hissing.
If I come further forward, even with no sudden movement or other threatening action, they will lash out with their tails with such force that each episode warranted enough worry of the front glass pane smashing. These animals will even ignore food offered to them, preferring instead to assume their defensive antics than eat immediately. (Feeding commences after all and any sight of a human – or even cats and dogs, for that matter – have vanished.)
Of course, drawing conclusions from observations of just two specimens are not enough, but there is no denying that these observations do say something. By contrast, captive individuals of Laguna monitors settle down rather quickly. When threatened or cornered, they resort to a fleeing response than standing their ground and assume a defensive mode. They may attempt to bite and empty out musk when handled, but this does not apply to all individuals.
This species begins to lose their fear of humans in just a matter of a few weeks, even becoming amenable to hand feeding; so strong is their feeding response that merely opening the enclosure triggers them into preparing a lunging action in anticipation of food.
Like other medium to large-sized monitors, these animals are quite adept at inflicting damage to their enclosures, particularly screens and doors, and the Sta. Maria specimen – supposedly V. dalubhasa – is no exception. But perhaps due to being a long-term captive, this animal has developed a habit of straying for only a few meters away from its enclosure upon escape. In at least three instances, it just stayed right beside its cage, giving me only casual glances and completely unperturbed as I make my approach. Behavior-wise, the two sister species (assuming here that the Laguna population represents V. dalubhasa) are worlds apart.
The authors placed emphasis on the importance of biogeography. A concept called the Pleistocene Aggregate Island Complex (PAIC) postulates that islands, or group of islands, surrounded by deep waters during the Pleistocene should have their own assemblage of species distinct from surrounding islands, based on the presumption that such deep waters would have prevented interisland species from crossing expanses on land exposed during the Ice Age. Presumably, ensuing isolation would have been enough a barrier to allow the evolution of distinct lineages.
Thus, when we take into account the distribution of varanids from the V. salvator complex within the Philippines, we see that Sulu has the enigmatic V. rasmusseni, V. cumingii is restricted only to Mindanao, V. nuchalis is distributed in the islands in the western Visayas, V. palawanensis occurs only on Palawan, and V. bangonorum is found on the islands of Mindoro and Semirara.
Still, the concept of PAIC can be somewhat questionable in some instances, as in the case of the striking V. samarensis, as the islands of Bohol, Leyte, Biliran, and Samar were previously connected to Mindanao during the last Ice Age, although it has been also postulated that the islands of Dinagat and Caraga would have served as a filter zone that barred the exchange of several species between Ice Age northern Mindanao (the eastern Visayas islands mentioned above) and southern Mindanao (the entirety of present-day Mindanao).
An even more abstruse instance is found in V. dalubhasa, which the authors stated to be distributed in the Bicol region, extending north to the town of Real in Quezon; its overlap with the range of the morphologically very similar V. marmoratus wasn’t clear, both from the time of the paper’s publication and to this day. Varanus marmoratus is now understood to occupy the rest of Luzon, plus the island of Lubang near Occidental Mindoro, and the island groups of Babuyan and Batanes. However, consultation with a few of my photos of what I perceived to be V. marmoratus from Laguna hinted at the possibility that V. dalubhasa, or at least those monitors that showed traits of that species, may well be present on the province. But it may not be as simple in other parts of the province. Recently, monitor lizards captured in the town of Kalayaan in the same province, but which I subsequently released, exhibited characters that were supposed to fit both V. dalubhasa and V. bangonorum.
According to the 2014 paper by Welton et al, V. bangonorum possesses “necks with gular region with characteristic dark blotches, becoming more prominent posteriorly” while for V. dalubhasa, they stated “gular region with irregular spots, faint anteriorly but becoming prominent and dark along lateral margins just anterior to gular fold.” Necks of V. marmoratus, in comparison, are typically obscured by dark pigmentation consisting of minute speckling all throughout.
So, what species do the Laguna monitors belong to?
The big question that needs addressing now is, what is the identity of the Laguna monitors?
At the time of V. dalubhasa’s description, the authors had 10 specimens examined, sampled from one municipality on Catanduanes island, one municipality each for Camarines Norte and Camarines Sur, three municipalities in Quezon, and on the island of Polillo. Eleven specimens of V. marmoratus were examined, from the islands of Batanes, Calayan, and Lubang, and on the Luzon proper in Ilocos Norte, Aurora, and Bulacan. No specimens were examined from the other southern Luzon towns surrounding Quezon, possibly due to the belief that what occurs in these areas are V. marmoratus.
If there is one fault I can ascribe to an otherwise well-written paper, it’s that it did not survey the provinces of Cavite, Rizal, and Laguna for Varanus. Doing so might have yielded additional insights into the distribution of V. dalubhasa.
The similarity of one Laguna specimen to V. bangonorum, at least with regards to the neck patterning, is even more perplexing, especially as currently understood, the species is restricted to Mindoro and Semirara islands. The deep waters around these islands are supposedly enough barrier to prevent the inter-island crossing of monitors, but what could possibly explain the V. bangonorum-like individual in Laguna?
One possible key to the mystery is that V. dalubhasa (assuming for the meantime that the Laguna population belongs to this species) is more variable than previously thought, and that in other parts of its range it displays patterning, particularly on the neck, approaching that of V. bangonorum. This possibility may have been overlooked by the authors of V. dalubhasa. The implication in this scenario is that the neck patterning is of no significance to the delimitation between both V. dalubhasa and V. bangonorum, and that the Laguna monitors have indeed be the former.
Nevertheless, one may begin asking questions if, due to a possible overlap of ranges on Luzon, V. marmoratus and V. dalubhasa are capable of reproducing and thus produce hybrid swarms. I personally am not equipped with enough tools to answer that, although it is certainly a possibility. After all, no one really knows at this juncture where the overlap exactly is, or if both V. marmoratus and V. dalubhasa share the same ecological niche in some unspecified locality.
For what it’s worth, it seems that the Laguna monitors do belong to V. dalubhasa, but the population exemplify how gular patterning is of very little use in distinguishing between it and the unrelated V. bangonorum – something that the authors weren’t aware of at the time of the two species’ descriptions.
In this vein, a point that I feel needs raising here is that there is a tendency among researchers to state that V. dalubhasa is endemic to the Bicol region, such as in a paper by Binaday et al (2017). Even without elucidating the species’ apparent presence in the province of Laguna, it was stated clearly in its protologue (Welton et al, 2014) that apart from the Bicol region, it also is found in both the province of Quezon and the island of Polillo.
This appeared in Animal Scene magazine’s October 2019 issue.