Every now and then we’ve had posts on this blog about non-anole lizards with anole-like dewlaps (e.g. 1, 2). Many agamids have flaps of skin under their throats that begin to resemble a dewlap, but male lizards in the South Asian genera Sitana and Otocryptis have the most “anoline” dewlaps I’ve seen so far. Indeed, some readers were almost fooled by Sitana’s resemblance, in both dewlap and dorsal patterning, to anoles. I spent the summer of 2012 documenting aspects of the display behaviour, morphology, and ecology of Sitana–here are some of my findings
Despite its ubiquity across much of peninsular India and Sri Lanka, Sitana remains relatively unstudied. Individuals across much of the range are classified as a single species, Sitana ponticeriana, despite substantial variation in dewlap morphology. It turns out that there are at least three dewlap variants, which occur, for the most part, in allopatry. Note the gradation in dewlap colouration between the three “morphs.”
The objective of my fieldwork was to see whether the morphs differ in display behaviour, the logic being that if you have different tools with which to communicate, then you would communicate differently. The morph with the intermediately coloured dewlap does not breed in the summer (because of geographical variation in seasonal rainfall), so I only visited populations of the white-fanned and coloured-fanned morphs. Here are two videos, which show, I think, how differently the two morphs display.
There were no substantial differences in habitat occupied by the two morphs, possibly because I sampled primarily in disturbed habitats such as agricultural fields and grazing lands, where both morphs persist well. Their persistence in such habitats potentially obscures differences in habitat structure under which this dewlap variation evolved. However, it also demonstrates that the morphs are not limited to different habitats by their dewlap morphology. Sitana are highly terrestrial (average initial perch height across all lizards observed: 18 cm!), which must contribute to their persistence in these tree-less and shrub-less habitats.
A possibility I’m sure many of you are considering is that the intermediately-coloured morph pictured above is a hybrid of the other two. However, this does not appear to be the case. Both the white-fanned and coloured-fanned morphs occur in sympatry at one of the sites I sampled (near Kohlapur, Maharashtra), and we spotted nothing that looked remotely like a hybrid or like the intermediate-fanned morph at this site. I suspect that the three morphs are different species, and a phylogenetic study of this species complex is underway in Praveen Karanth’s lab at the Indian Institute of Science, so my suspicion can soon be confirmed or proven wrong.
Finally, there’s been some discussion of whether the coloured-fanned males develop their colours anew every breeding season. My field assistant, Chetan Kokatnur, attempted to resolve this debate once and for all by returning to one of our field sites after the breeding season was over. Unfortunately, there were no lizards to be found! We’ll keep looking, and report back when we solve the puzzle. I’m also excited to observe the display behaviour of the intermediately-coloured males in the near future, which ought to lend further insight into how this dramatic variation in dewlap colour in Sitana might have evolved (not surprisingly, I think sexual selection might be involved, but I’ll save that for a later post).