A lot has been written about this Bayawak (click here for example). It’s huge (2 meters length), it has a double penis (which is not weird for reptiles), it only eats fruits (one of only 3, all can be found in the Philippines) and it has been discovered just recently. The team composed of Filipinos, an American, and a Dutch (from Leiden) have titled their paper in Biology Letters, “A spectacular new Philippine monitor lizard…” . Now you seldom see that in a scientific paper unless it’s really spectacular, spectacular!
Why is it spectacular is written above. But I think the finding is equally impressive because it suggests that there is a biological demarcation between north and south Luzon. So I will focus on the biogeography of this bayawak. I have a soft spot for biogeography as you would have guess from my post about the flat-headed frogs.
The range of species is limited to the northern Sierra Madre range and its closest relative, V. olivaceus lives south of Luzon. To the authors it is not surprising that there is a divergence in these species because the north and south Luzon are geologically separated. At present, three rivers bisects these regions. The presence of “topological, ecological and atmospheric barriers to dispersal has resulted in a more than 150 km gap” which isolated these species.
This hypothesis of the history of isolation according to the authors, is consistent to the observation of differences between its closest relatives. These are:
- the allopatric distributions of V. bitatawa and V. olivaceus on either side of these three low elevation valleys. This means these bayawaks to do not occur at the same place.
- the high levels of genetic divergence and sister relationship between the two taxa. This means they are very much related.
- the existing morphological differentiation between the two species. Most telling is the difference in the sexual organ.
What does this tell us?
- That there might be differentiation of other species similar to what they saw in the bayawaks.
- That there is an under rated biogeographic phenomena that is happening in Luzon and that is that “low-elevation valleys are barriers to gene flow in high-elevation forest endemic species.”
The authors conclude that
The discovery of a new Varanus adds to the recognition of the Philippines as a regional superpower of biodiversity.
And that leaves a spectacular feeling.
 L. Welton, C. Siler, D. Bennett, A. Diesmos, M. Duya, R. Dugay, E. Rico, M. Van Weerd and R. Brown,”A spectacular new Philippine monitor lizardreveals a hiddenbiogeographic boundary and a novel flagshipspecies for conservation”, Biol. Lett. 6, 654–658 (2010). DOI: 10.1098/rsbl.2010.0119.