Feed or Fight: Lizard Bite Force on Islands

Colin_With_LizardI’m a bit of an impostor here on Anole Annals, but I’m spending the year in the Losos lab writing up my dissertation and thinking about lizard evolution, so I wanted to share stories from some other island lizards “across the pond.

My dissertation work has focused on the Aegean Wall Lizard, Podarcis erhardii, common through much of the Greek archipelago. I’ve been surveying and experimenting with these lizards in different biogeographic and human contexts to connect trait changes to ecological surroundings. I recently published a paper looking specifically at lizard bite force. Since it comes with pretty pictures and is relevant to anoles, I want to share it here with you all.

For lizards, bite force is often important for determining what you can eat and how well you can fight off competitors. On small islands where food is often scarce, a proportionally stronger bite force might enable a lizard to access hard food items (like snails or beetles) or fight off other lizards, protecting access to mates, food, or prime nesting sites. Both explanations have been demonstrated in anoles: bite force has been closely tied to diet hardness (Herrel et al. 2006), and fighting success (Lailvaux et al. 2004).

I surveyed lizards on a dozen islands in the Cyclades. First, I found that lizards on small islands in the Greek Cyclades had significantly stronger bite forces relative to their body size. I then decided to try to untangle these two potential drivers (diet and aggression) and determine which better explained inter-island variability in bite force.

Donihue_FunEcol_Figure_1

By looking at proxies of competition including bite scars and missing toes, and lizard diets across islands ranging over five orders of magnitude in size, I found that, in general, it was the competitive environment that was driving the trend in P. erhardii bite force.

I’ve put together a short video about the findings for Functional Ecology (see above). For the full paper, please see:

Donihue, C.M., K.M. Brock, J. Foufopoulos and A. Herrel. 2015. Feed or fight: What drives bite force differences in the Aegean Wall Lizard, Podarcis erhardii, across the Greek Cyclades? Functional Ecology. doi: 10.1111/1365-2435.12550 Full text

Papers Cited:

Herrel, A., R. Joachim, B. Vanhooydonck, and D.J. Irschick. 2006. Ecological consequences of ontogenetic changes in head shape and bite performance in the Jamaican lizard Anolis lineatopus. Biological Journal of the Linnean Society 89: 443-454.

Lailvaux, S.P., A. Herrel, B. Vanhooydonck, J.J. Meyers, and D.J. Irschick. 2004. Performance capacity, fighting tactics and the evolution of life-stage male morphs in the green anole lizard (Anolis carolinensis). Proceedings of the Royal Society B: Biological Sciences 271: 2501-2508.

3 thoughts on “Feed or Fight: Lizard Bite Force on Islands

  1. Very cool study Colin!

    Weapon evolution is really cool. One thing that has often puzzled me is that as weapons become more dangerous, we might expect them to be less frequently used. I’d be really interested to hear your thoughts on this since it seems pretty well established now that bite force correlates with evidence of injury in Podarcis.

    One interpretation I guess is that stronger bites lead to proportionally more injuries we find evidence of, but are still used less frequently. Even so, aggression levels still seems to be higher in stronger biting lizards (based on the P. muralis I work on anyway).

    Maybe Podarcis never read a book on game theory?

    1. Very interesting. I agree that we’d expect as weapons become more dangerous they’d be used less frequently. I would really like to do the reciprocal behavioral studies to figure out if these small island, strong bite force lizards are actually more aggressive and if they use their bites in fights more or less often than others. To be honest, I could just as easily imagine the not game theory outcome.

      I have another idea about these bites and fights though. Across many of these same islands a coauthor found that the pressure needed to induce tail shedding increased significantly as island area decreased (Brock et al. 2015, Evolution). On small islands, despite the lack of predators, often nearly 100% of the population has signs of tail regrowth. I wonder if these strong bites might be used for taking the tails off of competitors, ending fights. It’d make sense too as a double positive – your defeated competitor loses those stores of energy in the tail, and you get to eat the tail and recoup energy lost from the struggle. Given the high rates of tail loss on predator-free islands I think some kind of system like this is at play.

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