Exercise Can Kill You (If You’re an Anole)!

Green anoles were trained, marked, released, and tracked in New Orleans. Photo by Jerry Husak.

In the US, we spend a lot of money trying to stay fit. This isn’t necessarily a bad thing, since there is a major problem with obesity and type II diabetes in the country. In humans, investment in increased performance abilities via the exercise response is also associated with numerous health benefits, such as decreased incidences of metabolic syndrome, cardiovascular disease, obesity, and diabetes, and aerobic capacity is considered to be an important predictor of longevity. However, it is these “side effects” that make exercise so interesting to an evolutionary biologist, because those wide-ranging, multi-system responses can tell us something about the evolution of animal life histories.

Superior locomotor performance has been shown to be advantageous to a variety of organisms in terms of male combat success, survival, and fitness. In addition, one of the most striking aspects of exercise physiology is how similar the response to exercise is across vertebrate animals, suggesting that the response to exercise is both ancient (yes, even fish respond to exercise!) and adaptive. However, until now, no studies have tested whether non-human animals that invest in increased athletic performance through exercise realize a fitness advantage in nature.

Jerry Husak and Simon Lailvaux set out to test whether superior performance after exercise training would increase survival probability in green anole lizards. Previous work with green anoles showed that they respond to different forms of exercise training, and that enhanced performance results in tradeoffs in other systems, such as reproduction and immnuocompetence. Why? Because performance abilities are energetically expensive to build, maintain, and use.

Urban islands in New Orleans where the study was conducted. Photo by Jerry Husak.

Jerry and Simon conducted their study in a New Orleans urban park that they cleared of existing lizards. They trained 30 lizards (15 male, 15 female) for endurance on a treadmill, 30 lizards for sprinting with weights on a racetrack, and had 30 untrained controls. All were released into isolated, urban islands in New Orleans, LA, USA and monitored for survival over an active season, over winter, and through the next active season. They predicted that training would enhance survival during the active season, but that the associated maintenance costs of training would decrease survival overwinter compared to controls.

This male made it a year in the wilds of New Orleans, but it looks like it was a rough year. Photo by Jerry Husak.

Contrary to expectations, they found that sedentary controls realized a significant survivorship advantage over all time periods compared to trained lizards. Trained lizards had reduced immune systems and lower fat stores, suggesting that in an environment with limited resources, it does not pay to exercise too much. These results suggest that locomotor capacity is currently optimized to maximize survival in green anoles, and that forcing additional investment in performance moves them into a suboptimal phenotypic space relative to their current environmental demands. We as humans can get away with it because we are not food limited. On the other hand, this is why doctors suggest consultation before going on a diet and doing intensive exercise training.

Source: Husak, J.F., and S.P. Lailvaux. 2019. Experimentally enhanced performance decreases survival in nature. Biology Letters 15:20190160. doi: doi.org/10.1098/rsbl.2019.0160.