Brachysaura minor is a medium-sized (60 mm SVL) agamid lizard from South Asia. It is one of very few agamids to vocalize (Vitt and Caldwell, 2014). Some individuals from this species produce a loud squeak when captured, probably as a defense. But this species also has some unique morphological characters, probably due to its terrestrial habit, including a stout body, short tail, short fifth toe, broad head with spines and large labial scales (Figure 1). Since its description (in 1827) this species has been placed in a variety of genera in the subfamily Agaminae based on external appearance.
Figure 1: An adult male Calotes (Brachysaura) minor from Wardhwan, Gujarat state, India.
In the recently published paper (Deepak et al, 2015), we used multiple lines of evidence (osteology, hemipenis and external morphology, and molecular phylogeny) to determine the systematic position of this species. These three lines of evidence suggest that Brachysaura minor is a Calotes and genetic data suggest that it is nested well within the widespread Asian genus Calotes which belongs to the sub family Draconinae (Figure 2). Calotes is one of the most common agamid genera in the Indian subcontinent. Most species in this genus perch on vegetation, with some species like Calotes grandisquamis and Calotes nemoricola living higher up in the rainforest trees in the Western Ghats. Calotes minor on the other hand is a completely terrestrial species, found in open grasslands perched on small rocks.
Figure 2: Bayesian tree inferred from mtDNA data in MrBayes 3.2. The values assigned on the internodes indicate maximum likelihood bootstrap values, dark circles indicate posterior probability support above 95% and light circles indicate less than 95% probability. From Deepak et al. 2015.
A general trend in agamid lizards is that “the length of the tail does not correlate with the number of caudal vertebrae” (Moody, 1980). Interestingly, there are some outliers in this trend: the short-tailed, terrestrial Calotes minor and its very distantly related cousin from southern parts of Africa, Agama hispida, both have fewer caudal vertebrae than their sister species. The ground dwelling Moloch horridus from Australia and Xenagama batillifera from the horn of Africa also have the same range of caudal vertebrae (Moody, 1980). Relative to body length, Calotes minor has the shortest tail length compared to many other Calotes (Figure 3A). On the other extreme, the arboreal Calotes calotes has the longest tail among Calotes (Figure 4). They live on trees in southern India and Sri Lanka.
Figure 3: Plot of body measurements of Calotes minor (blue circles (males), red circles (females)) compared to other known Calotes spp. (Blue triangles (males), red triangles (females)). Black circle sub-adult male. A) SVL versus tail length of 17 out of the 25 described species of Calotes. B) SVL versus fifth toe length of 9 out of the 25 described species of Calotes.
While the above pattern may suggest that short tails have evolved repeatedly in terrestrial agamids, both Sitana ponticeriana and Otocryptis wiegmanni, which are terrestrial, have very long tails. However, another trait is shared by the terrestrial Sitana and Otocryptis, namely the extreme reduction (Otocryptis) or loss (Sitana) of the fifth toe. Therefore, we decided to look at the fifth toe length in relation to SVL in Calotes minor as well. The completely terrestrial Calotes minor has the shortest fifth toe compared to many of its arboreal sisters (Figure 3B). In western India and parts of central India, there are vast expanses of open grasslands with only few rocks embedded in it and Calotes minor may have evolved to occupy these niches.
Figure 4: Calotes calotes from Rameshwaram Island, Tamil Nadu state, India.
Citations:
Moody, S.M.(1980): Phylogenetic and historical biogeographical relationship of the genera in the family Agamidae (Reptilia: Lacertilia) – Thesis, The University of Michigan, Michigan, 373 pp.
Vitt, L.J. and J.P. Caldwell. (2013). Herpetology, Fourth Edition: An Introductory Biology of Amphibians and Reptiles 4th Edition. Academic Press, San Diego.
Russell A.P. and Rewcastle S.C. (1979): Digital reduction in Sitana (Reptilia: Agamidae) and the dual roles of the fifth metatarsal in lizards. Canadian Journal of Zoology 57: 1129-1135.