Tag Archives: tail autotomy

Predation, Food Abundance and Male-male Fighting Drives Natural Variation in Lizard Tail Autotomy

If you have a truly outstanding memory or if you enjoy re-reading old AA articles, you might remember this post on how bolder lizards autotomized their tails more readily to compensate for risky behavior. As unlikely as it is, you might also remember me saying that this study solved one piece of the puzzle by explaining why the propensity of tail autotomy would vary within a population. Two years have since gone by, and I am glad to present to you, my fellow AA readers, another piece of the puzzle: how ecology might shape the variation in tail autotomy among populations.

A side-blotched lizard couple snuggling (or more accurately, avoiding human nuisance that was the researcher)

A side-blotched lizard couple snuggling (or more accurately, avoiding human nuisance that was the researcher)

Which aspects of ecology should we be looking at? Fortunately, the rich literature in tail autotomy helped us identify three main players: predation, food abundance and male-male fighting. Among these three ecological factors, the relevance of predation is the most straightforward: lizards will benefit from autotomizing more readily if predation pressure is high. On the other hand, the importance of food abundance lies in the fact that lizards need resources to grow the tails back, and the rate of regeneration depends on food abundance. Therefore, high food abundance will allow for faster regeneration and likely favors higher propensities for tail autotomy. The inclusion of male-male fighting as a key factor stems from the common observation that the tail is a common target for attack when males engage in territorial combats. In fact, quite a few studies have reported tail autotomy as a consequence of male-male fightings. As fights between males are rarely life-threatening (i.e. autotomy-worthy), tail autotomy under those circumstances would be undesirable. Consequently, environments in which male–male combat is common should favor lower autotomy propensities, with other things being equal.

To test these hypotheses, we first built a theoretical model in which we simultaneously varied predation, food abundance and the degree of male-male fighting and examined the propensity for tail autotomy that conferred the highest survival. Results from the model supported our hypotheses: higher predation and higher food abundance favored higher autotomy propensities, whereas higher intensities of male-male fighting favored the opposite. We then took one further step: we collected data on these three factors from five populations of side-blotched lizards (Uta stansburiana) in the western U.S. and used our model to explain the variation in the propensity for tail autotomy among those populations. It turned out that our model did a pretty good job, and we are confident that the variation in tail autotomy at the population level represents the outcome of ecological adaptations to predation, food abundance and male-male competition.

Are you wondering which of the three factors played the most important role in determining the propensity for tail autotomy (hint: it was NOT predation!)? Are you interested in more details about how we actually constructed the model? If so, you might want to give our recent paper a read:

CHI-YUN KUO and DUNCAN J. IRSCHICK. (2016). Ecology drives natural variation in an extreme antipredator trait: a cost-benefit analysis integrating modelling and field data. Functional Ecology 30: 953-963. doi: 10.1111/1365-2435.12593

Bolder Lizards Drop Their Tails More Readily to Compensate for Risky Behavior

(editor’s note: this video was added by the editor. Decide for yourself whether it illustrates the experimental approach described below)

It’s no secret that grabbing a lizard by its tail will often times leave you with the tail rather than the lizard. Why? Because the tail would simply break off. The voluntarily shedding of the tail in lizards (tail autotomy) has fascinated herpetologists ever since the 70s, and it didn’t take long for those people to notice that the propensity for tail autotomy varies extensively among species, conspecific individuals, or even within the same individual at different developmental stages. Four decades have passed, what might be responsible for the variation in tail autotomy is still not entirely clear. In a recent paper, we tried to solve a piece of the puzzle by testing the hypothesis that lizards might autotomize the tail with different propensities to compensate for their intrinsic risk-taking tendency.

Our idea was simple: bolder lizards, due to their behavioral tendency, tend to expose themselves more to higher predation risk. Therefore, selection might favor higher propensities for tail autotomy in bolder lizards as a compensation mechanism. We were also interested in knowing how food availability in the environment might affect tail autotomy. So, we caught a bunch of juvenile brown anoles from the same population in New Orleans and assigned them into two dietary groups: low versus high food availability. After the lizards reached adulthood, we picked out the males and examined the relationship between boldness and the propensity for tail autotomy. (In case you wonder how we measured the propensity for tail autotomy, we refer you to a paper by Stanley Fox, who contributed greatly to our knowledge of tail autotomy.)

And here’s what we found:

The relationship between boldness and the propensity for tail autotomy in the brown anole lizards

Bolder lizards did autotomize their tails more readily as a means to compensate for their risk-prone personality, but only in the group raised with abundant food. Our results helped explain why lizards from the same population autotomized the tail with different propensity. Moreover, our study highlighted the role of food availability in the cost-benefit dynamics of tail autotomy, which has never been explicitly discussed or tested before. Aside from those exciting implications for the study of tail autotomy, our results also have important bearings on broader topics such as the evolution of trait compensation and animal personality. If you are interested in knowing more about this project, check out our recent paper:

CHI-YUN KUO, DUNCAN J. IRSCHICK and SIMON P. LAILVAUX. (2014). Trait compensation between boldness and the propensity for tail autotomy under different food availabilities in similarly aged brown anole lizards. Functional Ecology DOI: 10.1111/1365-2435.12324