In recent months, there has been a lot of talk on the Auburn campus about multimodal signals. Diana Hews gave a phenomenal seminar to the Biology Department last November about complex signaling in Sceloporus lizards, and just last week Eileen Hebets told a similar story about signaling behavior in a group of invertebrates, amblypygids. The latter lecture prompted a momentary side conversation between a Warner Lab postdoc, Tim Mitchell, and me concerning the apparent lack of multimodality in Anolis signaling. Ironically, I just ran across a 2016 publication by Baeckens et al that forced me to eat crow, albeit only a tiny bit of crow.
Anoles, like most iguanians, have been labeled as “visual only” signalers and for good reason. Anoles lack the epidermal glands that secrete the typical chemicals used in lizard chemosensing. Rather, anoles are known widely as models for communication for their reliance on visual signals (which have been demonstrated to be quite complex despite being unimodal) and are also characterized by a low baseline rate of tongue-flicking, even when considered against the backdrop of other visually oriented iguanians. Additionally, previous experiments conducted with A. carolinensis found no significant evidence of chemosensory function in prey selection, assessment of opponents, or in mate choice (Jaslow & Pallera, 1990; Forster et al., 2005; Orrel & Jenssen, 2002). The question of whether or not anoles utilize chemical signals seems to be one answered; however, Baeckens et al have conducted a simple but convincing study that might demonstrate the converse.
Each of 14 male A. sagrei were placed alone into an enclosure with opaque walls on all sides (though one wall was coated with a dark window film so males could be observed). This was done under two different conditions. On one occasion, the enclosure had been recently cleaned with ethanol and on the other, the cage had previously housed several female sagrei for at least eight hours. The females were then removed just five minutes prior to the male’s introduction. The placement of males in each treatment was randomized; however, each male was subjected to both conditions and cages were cleaned between trials. During each trial, the researchers measured the amount of signaling (number of headbobs, dewlaps, pushups) and exploratory behavior (number of tongue extrusions and locomotor behavior) performed by the male being tested. They found that males displayed significantly more dewlap extensions and headbobs as well as more tongue flicks and locomotor activity when placed in a novel cage that had recently housed female anoles than when placed in a control cage (Fig 1). This, they claim, “[constitutes] the first evidence of intersexual chemo-sensation in an anoline lizard.”
Though intriguing, these data cannot be separated from the immense body of literature that overwhelmingly demonstrates the reliance of anoles on visual communication. for example, even though males in this study performed many more displays when in a cage previously occupied by a female, other studies (i.e. Driessens, Vanhooydonck & Van Damme, 2013) demonstrate that signaling behavior can still be as much as nine times greater than that observed in the current study when males have visual contact with a female, and thus chemosensory functions that may be in play still pale in comparison to the use of visual signaling. What is yet to be determined is the ecological relevance of such signaling and the extent to which it may enhance visual signals. One proposed explanation for the importance of multimodal signaling is that each signal alone does not produce the magnitude of response that the two signals produce together. It will be for future studies to determine if visual signaling in anoline lizards is somehow enhanced by chemosensory function. The results of this study, however, are quite enticing and further illustrate why anoles make phenomenal models for studying communication.
assorted facets of the dewlap, in both sexes of Anolis sagrei. Behavioral Ecology and