Author: Ambika Kamath Page 5 of 6

When videotaping Sitana last year, I noticed an odd interaction between a male and female, wherein the female suddenly ran towards the male, and after he displayed a little bit at her, she sat on him. She remained there for a couple of minutes, and then ran away.

Anolis cristatellus female sitting on male (photo by Kristin Winchell)

I had no idea what was happening–there were at least two more females in the vicinity, and I wondered if this sitting behaviour was an instance of female competition over the male. But I didn’t see the behaviour again, and thought no more of it until Kristin Winchell mentioned that she had seen similar behaviour in her captive Anolis cristatellus, being housed in male-female pairs for a common garden experiment. Moreover, she has noticed the same pairs repeatedly engaging in such interactions. Any thoughts on what might be going on?

Anolis cristatellus female sitting on male (photo by Kristin Winchell)

A previous discussion on this blog has raised the following question: in which situations is a lizard most likely to lose its tail? Common wisdom has it that tails are most frequently lost in the avoidance of predators, and observational evidence backs this up, at least in the case of anoles–no AA reader has observed tail loss in a male-male aggressive interaction. But what about other lizards?

In Sitana ponticeriana, an agamid lizard that I often post about on this blog, a couple of observations point to the likelihood of male-male competition as a driver of tail loss. Tail loss is not uncommon–in the locality I have sampled best, 13.5% of lizards have lost their tails. Males are about 1.7 times as likely to lose their tails as females (16.5% of males vs. 9.6% of females). Further, lizard predators aren’t too common in this locality–fewer than 30 individuals of potential lizard predator species were spotted or heard in over two months of sampling, and no predation attempts were observed.

But more excitingly, I had the chance to observe firsthand the loss of a tail during a male-male fight this summer! The resident lizard had lost much of his tail prior to the fight, a measly 5.4 cm remaining. The intruder, however, had an almost complete tail. Here is a rather blurred photo of the two males facing each other:

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The best anole fossils have been found in amber [e.g. 1,2]. Amber is, of course, fossilized tree resin, and I have often wondered how likely it would be that a lizard would manage to get itself stuck in tree resin. After all, as we know from catching them, small lizards are nothing if not agile.

Sitana ponticeriana is a small agamid lizard found in dry habitats across South Asia. Though most commonly found in disturbed, open habitats, they also occur in the rapidly dwindling stands of thorn scrub forest found across India.These forests are dominated by resin-producing Acacias, and are being invaded by the resin-producing Prosopis juliflora.

Acacia forest in Kutch, India

This sort of forest is exactly where you might expect to find lizards interacting with resin, and here is an example. This female Sitana ponticeriana, caught in the forest shown above, had a finger on her front foot completely stuck in a little ball of resin. It is easy to imagine how a slightly smaller lizard or a slightly larger piece of resin could result in an inextricable lizard and, in several thousand years, a very cool fossil!

Female Sitana ponticeriana with resin stuck to her toe

Avid readers of this blog might have noticed that Jonathan Losos likes trying to get readers to confuse the white-fanned variant of the South Asian agamid lizard Sitana ponticeriana with the only toepad-less anole, Anolis onca. Indeed, the two lizards look quite similar:

Sitana ponticeriana, white-fanned variant, in Saswad, India

Anolis onca in Maracaibo, Venezuela. Photo by Jonathan Losos

Posts [1, 2, 3] detailing the habits and habitats of these two lizards point to a number of similarities between the species. Both occur in incredibly hot and windy environments. Both are primarily terrestrial, where they are very well-camouflaged, but are also observed perching on vegetation. The causes for the loss of A. onca’s toepads remain a mystery, and here I lay out some observations of S. ponticeriana’s behaviour that lead to a hypothesis for why A. onca might have lost it’s toepads.

Perch use in S. ponticeriana follows a predictable temporal pattern from about 8:00 a.m., when the lizards first emerge, to about 12:00 noon, the hottest part of the morning. Lizards perch primarily on rocks, if available, in the early morning while basking. During the middle of the morning, male lizards are found perching on and displaying from a variety of perches, including the ground, mud piles, rocks, twigs, and shrubs. By noon, however, lizards are often found resting in shrubs. Here are a couple of lizards resting:

Male Sitana ponticeriana, white-fanned variant, resting in the shrubs. Saswad, India.

Female Sitana ponticeriana, white-fanned variant, resting in the shrubs. Kutch, India.

But what happens when you chase lizards out of the shrubs in the heat of the day? Peak air temperatures at the site I was at this summer hovered around 40 degrees Celsius, and soil or rock surface temperatures were likely higher (they certainly felt so). Lizards that we chased out of shrubs onto the sand would run rapidly as usual, but when they paused, were often observed lifting the toes of their hind feet off the ground. Here are two photos–compare the toe positions on the hind foot to get a sense of the behaviour I’m referring to:

If the highest risk of heat exposure comes from the ground, any adaptation that reduces the transfer of heat from the ground to the lizard will be favoured. Such adaptation would explain S. ponticeriana’s behaviour of resting in vegetation during the hottest part of the day and lifting toes off the ground when forced onto hot terrestrial perches. Like most agamids, Sitana have very skinny toes, leaving a small surface area for transfer of heat from the ground. But what about A. onca? If the ancestral A. onca had typically anole-like toepads on moving to the beaches, they might have been at high risk of heat transfer from the sand when forced onto terrestrial perches in the heat of the day. This would lead to the evolution of reduced toepads to avoid such heat transfer. A temporal pattern of perch use in A. onca, similar to that of S. ponticeriana, would be the first piece of evidence useful for establishing what might be an exciting example of trans-continental convergence.