What Does The Dewlap Say?

Cusick_FL_sagrei_1dewlapIf you followed the barrage of blogposts we wrote from SICB 2014, you might recall some discussion of the information actually conveyed by anole displays and dewlaps (1, 2). The upshot of these studies is that anole displays are complex. We see unexpected relationships between various traits and the probability of success in male-male competition, and different traits correlate with different measures of male success. A recent study by Steffen and Guyer (2014) adds to our growing knowledge of the information conveyed by different dimensions of multimodal anole displays. When viewed together with previous research, this study presents us with an even messier picture than before of how Anolis lizards communicate with each other.

Steffen and Guyer (2014) set up paired competitions between size-matched male Anolis sagrei in a lab setting, implementing two treatments–males either compete for access to a single perch, or for mating access to a single female. All interactions were recorded, and display behaviours–headbobs, push-ups, dewlap extensions–were quantified. Further, the spectral reflectance of both the centre and the margin of the dewlap (which can be strikingly different in A. sagrei) was also measured. The question asked by the paper was straighforward: which display and dewlap traits are related to an individual lizard’s status as a winner or loser of competitions?

In both competitive contexts, only two traits seem to be important–a composite axis of behavioural variation, and one of three composite axes describing the colour of the margin of the dewlap. Lizards who headbob, push-up, and extend their dewlaps more during competitive interactions are more likely to win than lizards who display less. Curiously, lizards with lower UV reflectance of the dewlap margin are more likely to win than lizards with brightly UV-reflecting dewlap margins.

Of the two variables, display behaviour was more highly correlated with the probability of success than dewlap margin UV-reflectiveness. I’m curious about how the two variables are themselves related–do lizards  that display more also have less bright dewlap margins? The authors propose that a dewlap’s reflectance might relate to its conspicuousness, and it would be interesting to know if different individuals are conspicuous in different ways.

Each of the studies conducted so far on how anoles convey information to each other has examined different dewlap and display variables, studied different competitive contexts, and used different measures of male quality. It therefore isn’t surprising that we seem far from reaching a consensus on what the dewlap says.

 

 

8 thoughts on “What Does The Dewlap Say?

  1. Awesome stuff Ambika!
    Any conjecture, on a minor tangent, as to why A. carolinensis, A. sagrei, and even A. equestris (not to mention Iguana iguana), will often head bob and or dewlap display to humans? I just had this happen with an A. carolinensis male on a stalk. It saw me, bobbed 3 or 4 times, and then let me see what he was worth pink dewlap style. How does this work? Is he hoping another anole SEES him do this to ME? :-)
    Best,
    Kenny

    1. The usual explanation for such behaviour is “pursuit deterrence,” which means that lizards display at creatures they think might be predators to indicate that they’ve spotted the predator and will be able to escape, so it isn’t worth the predators time/effort to chase after them.

  2. Ambika, for those of us not was well versed in this literature, what do you mean by “different measures of male quality”? Just how many different measures have been used and is there any logical relationship between them (whether quantified or not)? Are these different measures driven by field versus laboratory studies where different amounts of control are possible? I found myself thinking about this seemingly minor comment for several hours this afternoon so I thought I would just ask.

    1. Gosh, sorry to cause you so much puzzlement, Thom! All of these measures of “male quality” seem to function as proxies for reproductive success: the probability of winning a competition (this study, and Jordan Bush’s poster at SICB ’14), territory size (Jordan Bush’s poster), performance variables such as sprint speed or jumping ability or bite force, and immunocompetence (Tess Driessen’s talk, SICB ’14). The differences among studies seem partially explained by what variables are examined in the first place. The lab/field difference is explored nicely by Jordan’s work, which questions whether these different measures of quality are actually related in ways we expect. Links to descriptions of both these other studies are in the post.

      Thanks for asking me to clarify the phrasing–I shouldn’t have taken it for granted!

      1. Thanks. I wasn’t sure if that comment was meant to go beyond those studies into the bottomless pit of anole literature. Either way, it seems like a critical step towards consensus is to standardize the proxies on male quality. Its fun to think about and probably difficult to operationalize.

  3. Yeah, I think the key step will be understanding how each of those measures actually relate to reproductive success, ideally in a variety of different contexts.

  4. There are a lot of problems with the way that male “quality” is conceptualized and measured generally, and this is one of my current pet peeves. Ambika, I think you are right in that this is exactly what needs to be done. For those who are interested (and at the risk of some blatant self-promotion), a review that discusses these and related issues can be found here

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