Over the years, there has been a lot of discussion on Anole Annals about the large, conspicuous dewlap. And rightly so because it is arguably the most evocative feature of the anoles. Much of this discussion has focussed on its function, such as its role in species recognition, mate choice, and territorial communication. But is there a cost to having such an audacious visual signal?
We needn’t isolate this question to just Anolis lizards. All socially communicating animals need to produce a signal that will be obvious to conspecifics. There’s little point producing a mating or aggressive signal if females or rivals never detect it. But there is a cost to being conspicuous and it can be a matter of life and death: the unintended attraction of predators.
Generally, the assumption has been that animals just incur the potential risk of predation for the sake of successful communication. But just how risky is it? The dewlap is often large and brightly coloured, but when it’s not being used in display, you’d never know anoles even had one.
There are also at least two other independent origins of the dewlap, including in the gliding lizards of Southeast Asia, the Draco. In these lizards, the dewlap is again large and often conspicuously coloured.
For both Anolis and Draco, one of the best ways to find lizards in the wild is by the quick flash of colour as males rapidly extend and retract the dewlap during their territorial displays. In fact, it is often the only way to find Draco, which are camouflaged and extremely difficult to spot, even when you happen to be staring right at them.
I had this crazy idea a few of years ago… Would it be possible to build an army of robotic Draco lizards with plasticine bodies that could retain impressions of predator attacks and measure the risk of predation from performing a conspicuous dewlap display?
It really was a ridiculous thought, but my long-time collaborator Indraneil Das was game.
And it worked, with the results just published.
Robotic lizards compared to the real thing in (a) morphology and (b) behaviour (robots were modelled on Draco sumatranus from Borneo).
It was an awful experiment to do. Building the robot army turned out to be the easy bit. To be clear, it took months of development and manufacture, all of which I did in my garage (long story). It then took years to run the experiment, with multiple replications across two continents because the data was puzzling. There were bushfires, floods, battles with swarming wasps and kamikaze leafcutter ants, chipped teeth, falls from ladders, bogged car rentals, hammered thumbs, and in the end I only just managed to get it finished before the world turned side-ways in 2020.
Left: fresh-faced and optimistic in June 2018; Right: brave-faced but really a little shellshocked with the retrieval of robot 2,120 in February 2020 (NB: batteries have a habit of failing and parts started to corrode so only 1,566 robots were fully functional in the experiment).
It turns out that prey that can produce a signal intermittently — effectively turning their conspicuous display on and off at strategic moments, like the dewlap — can drastically reduce their risk of predation. In fact, attack rates by predators on dewlapping robotic lizards were no different to robots that remained unmoving and cryptic in the environment. Which means there doesn’t really seem to be a large cost from increased predation for animals that perform bouts of conspicuous behaviour.
But this wasn’t the biggest surprise.
The experiment included robotic lizards that kept the large, conspicuously coloured dewlap permanently extended so it was always visible. Think of peacocks with their massive tail trains or other animals that are spectacularly ornamented. These features are always visible and are not signals that can be turned on and off. My assumption was that these robotic lizards would be the hardest hit by predators.
This wasn’t the case at all. Predators actually avoided these robotic prey and to such an extent that the probability of attack was lower than the robotic lizards that remained cryptic and didn’t perform any conspicuous behaviour.
Photo montage of predator attacks left in the plasticine body of the robotic lizards
At first, I found this to be confusing and replicated the experiment over and over again. I even called in my partner Katrina Blazek who is a biostatistician to blind the data and independently perform the analyses (Katrina is also a skilled tailor and made all the robot dewlaps). I also dragged in my colleague Tom White who is an expert on animal colour discrimination to confirm that the dewlap really was as conspicuous to predators as I thought it was.
The data was robust.
This type of predator phobia actually helps explain the evolution of a completely different type of animal signal in nature: aposematic signals or warning signals that some prey evolve to explicitly advertise their location to predators to warn them against attack, usually because they’re toxic. Conspicuous poison dart frogs are an obvious example, so are ladybirds (or ladybugs).
The paradox is how these warning signals could evolve in the first place given the first individuals that tried to advertise their warning would be quickly eaten by predators that had no idea the signal was meant to advertise unprofitably until after the attack.
One of the key hypotheses that has been proposed to resolve this evolutionary paradox is that predators are highly conservative in the types of prey they go for. That is, they tend to avoid prey that look unusual in some way, even if those prey are more easily detected.
This is exactly what happened in this experiment. The robotic lizard with the permanently extended dewlap was ‘weird’ and so predators instead targeted the robotic lizards that either displayed intermittently or remained cryptic, both of which were more typical of their familiar prey.
The take home message is:
Follow your ridiculous idea and call on your friends to help.
(But don’t hold metal tools between your teeth. Your dentist will be very annoyed with you.)
- Dewlap Displays Supersede Headbobs, Yet Again - March 11, 2023
- Dewlap Size Is Not What We Thought - October 14, 2022
- Do Anoles Display with Greater Complexity than English? - July 10, 2022
Jim
Amazing!