Author: Tess Driessens

For decades, we anole scientists have been fascinated by the marvelous throat fans, called ‘dewlaps,’ characterizing Anolis lizards. A bunch of brilliant studies have therefore focused on the origin, evolution, diversity and function of this structure, revealing important pieces of what seems to be a complex ‘dewlap puzzle.’ And I think you all agree that the answer to what might look like a rather simple question at first, i.e., ‘what does the dewlap say,’ is not evident at all. So, with our study we aimed to add an ‘extra’ piece to the puzzle, which may help to further unravel the exact nature of information conveyed by the Anolis dewlap.

We specifically focused on what is signaled by various components of the dewlap in the brown anole and whether diverse aspects of dewlap signaling provide additive information or highlight different characteristics of the sender. We therefore measured several dewlap components involving design (i.e., dewlap area, patterning, and color) and use (i.e., dewlap extension frequency during intersexual interactions), and linked these to information a sender may need to transmit in order to increase its fitness (i.e., sexual identity, individual quality, and social status). We used several performance (i.e., bite force, sprint speed, and clinging capacity) and health state parameters (i.e., immunocompetence, hematocrit, and swelling response) as a measure of individual quality, whereas mirror-motivated aggressiveness was used as a measure of social status. Due to their fundamentally divergent reproductive roles, we expected males and females to differ with respect to what is signaled by the dewlap, and therefore performed separate analyses per sex. For the male sex, we additionally distinguished between the color of the dewlap center and edge region.

What did our results show?
First, we found that body size together with relative dewlap area and color act as redundant messages in the advertisement of sexual identity. Depending on the distance between signaler and receiver and prevailing environmental conditions, recognizing a potential mating partner based on the estimation of its body size only may be a hard task to fulfill. We therefore suggest that repeating the same message in different ways using body size together with dewlap traits is a highly appropriate strategy to get information about sexual identity accurately across.

Second, we found that dewlap coloration is primarily responsible for signaling aspects of individual quality, but only in males. Our results show that individual health state parameters are reflected in the color components of both male dewlap center and edge and that multiple different messages are conveyed by dewlap color. Specifically, we found that males bearing dewlaps with higher amounts of yellow and red and lower amounts of UV show higher body condition indexes, and that individuals with generally brighter dewlaps have lower immunocompetence. In addition, males with more yellow and UV chroma in dewlap edge only exhibit higher hematocrit values.

Surprisingly, none of the tested components of dewlap design in A. sagrei males conveyed information on performance capacities and aggressive behavior, and the same result was found for dewlap use. Also, no links were observed between components of dewlap design and use during intersexual interactions.

Third, for females, neither dewlap design nor use were related to any of the tested individual quality measurements and mirror-induced aggression. However, in contrast to males, correlations between components of dewlap design and use were found in A. sagrei females. Female individuals with larger dewlaps showed higher dewlap extension frequencies during intersexual interactions only and the same is true for individuals with less bright dewlap centers, suggesting an important signaling function of the female dewlap during courtship.

What can be concluded?
Our study confirms that the dewlap signaling device is a very complex integrated system consisting of different components transferring redundant (sexual identity) as well as non-redundant information (individual quality). We found that both the dewlap center and edge bear a signaling function, but this was only tested in males. As expected, male and female dewlaps differ in the messages they convey and further research is absolutely necessary to get insights in ‘what the dewlap exactly says’.

Driessens, T., Huyghe, K., Vanhooydonck, B. and Van Damme, R. (2015). Messages conveyed by assorted facets of the dewlap, in both sexes of Anolis sagrei. Behav. Ecol. Sociobiol. DOI 10.1007/s00265-015-1938-5

Display Behaviour in Anolis sagrei: Deterring Predators, Daunting Opponents or Drawing Partners?

By Tess Driessens

On February 6, 2014

In All Posts, New Research

Male and female A. sagrei at the famous Soroa, Cuba locality.

Anole displays consist of conspicuous behaviors that are known to be used in multiple contexts, such as exhibiting territory ownership and territory defense, mate attraction and female receptivity, species recognition, and even predator deterrence. As most of you know, the display repertoire typically involves three major signal types: “dewlap extensions” (DE, pulsing of the throat fan or dewlap), “push-ups” (PU, up and down movement of the body and tail), and “head-nods” (HN, up and down movement of the head only). Although the visual display behavior in anoles has been extensively studied, the function of these three major signal types (DE, PU and HN) remains highly equivocal, and especially in the brown anole. Therefore, we decided to set up a behavioral experiment addressing DE, PU and HN signaling rates across diverse contexts, using the brown anole as study species.

Our study differed from previous ones in two main aspects. Whereas most other studies have focused on male signaling only, we looked to the three separate signal types in both male and female lizards. Secondly, our study is the first one to compare display rates across a wide range of contexts using the same individuals over again (repeated-measures design). This design could, however, only work under fully-controlled laboratory testing conditions. The diverse contexts we tested included predator, non-predator and several social interactions (i.e., mirror, male-male, male-female and female-male). For the predator and non-predator interactions, we used a living curly-tailed and equally-sized ocellated spiny-tailed lizard, respectively; the social context involved only conspecific interactions. Rather than examining display structure, we focused on the frequency with which each individual signal type was performed.

What did our results show? We found that brown anoles of both sexes exhibited higher display rates in the presence of conspecifics than when confronted with a predator or non-predator. DE, PU, and HN seem to be of main importance during brown anole social interactions, and thus not in predator deterrence. Whereas the females did not significantly raise display rates in response to a mirror or during intersexual interactions compared to a control situation, males did. The PU signal type only appears to play a major role for brown anole males during aggressive encounters. On the other hand, increased frequencies of all signal types during male-female interactions suggest that DE, PU, and HN are all essential for male courtship.

Staged intersexual interactions in the brown anole

Finally, we suggest that intersexual selection is probably a driving force for frequency-related dewlap use in both sexes (we found a very strong, but not significant, trend that females increased their DE frequency only during female-male interactions). In contrast, pronounced intersexual differences were detected for PU and HN rates within a social context. I would like to mention once more that all our behavioral experiments were conducted under controlled laboratory conditions and that caution is needed on the general interpretation of our findings.

To end, I would like to say that we did experience some difficulties in comparing our PU and HN results with results from previous studies on brown anole display behavior, due to an inconsistent terminology found in the literature. Authors have variously used the terms “nod,” “headnod,” “bob,” “headbob” and “pushup” to refer to the stereotyped bobbing display and it is not always clear which movements correspond exactly to which terms (e.g., only head movement, only front legs, whole body movement including/excluding tail). Partan et al. (2011) did a very nice job by discussing several bobbing display terms in her paper, but still we think there is need for a more consistent and defined “bobbing” terminology. In this way, pooling display datasets and comparing display results will become more efficient and accurate, which in turn may lead to better “anole science”!

Driessens, T., Vanhooydonck, B., Van Damme, R. 2014. Deterring predators, daunting opponents or drawing partners? Signaling rates across diverse contexts in the lizard Anolis sagrei. Behav Ecol Sociobiol 68:173–184.

Curly-tailed Lizards Eat Brown Anoles… Not On Cayman Brac!

By Tess Driessens

On April 6, 2013

In Natural History Observations

Within the framework of my PhD, I examine what determines dewlap diversity in Anolis sagrei and aim to improve understanding of the morphological, performance and behavioural variation within this species on diverse Caribbean islands. Last month I was sampling a few brown anole populations on the Cayman Islands and I encountered some interesting curly tail – brown anole interactions, which might be worth mentioning on Anole Annals. Previous observations have shown that curly tails (Leiocephalus carinatus) do eat a lot of anoles, including A. sagrei; see previous posts (<1>, <2>, <3>, <4>)

Curly-tailed together with plasticine anole model on Cayman Brac

Our sample site at Cayman Brac consisted of a very dense brown anole and curly-tailed population living together. To make an estimation of the relative predation pressure, I generally place 120 plasticine anole models per sampling site and recollect them after 48 hours to score for predation marks. Because of the high abundance of curly tails on our site in Cayman Brac, I expected to recollect many attacked plasticine models, but instead… (see pictures). The curly-tailed does not intend to attack the model, but is trying to copulate with it! A rather unexpected observation from my point of view. Of course, the models are not moving and the chemical cues are completely absent, but still… Furthermore, I made lots of behavioural observations on A. sagrei individuals and had the impression that they didn’t care at all about the presence of curly tails close by. The brown anoles were often perching within less than 1.5m of a curly-tailed and still very relaxed; and vice versa, the curly tails didn’t really care about the brown anoles sitting near. In contrast, when a red-legged thrush (Turdus plumbeus) was approaching, all anoles in the close surroundings escaped very fast.

Conclusion: it seems that curly tails on Cayman Brac ‘love’ their prey…