SICB 2017: Testosterone Influences Dewlap Expression and Energetics

Above: Albert Chung presented on how testosterone influences sexual signals and energetics at the annual Society for Integrative and Comparative Biology meeting in New Orleans, LA.

Many researchers are curious about how sexual signals evolve and if those signals are influenced by an individual’s energetics. Signal expression (such as anole dewlap size or color) and energetics might have the same physiological underpinnings, and signal expression may be limited by energetic state. Albert Chung, a graduate student working with Dr. Christian Cox at Georgia Southern University, along with graduate student, Aaron Reedy, and Dr. Robert Cox at the University of Virginia tested this hypothesis with brown anoles (Anolis sagrei) in the lab and in a wild population in the Bahamas.

The researchers had three different groups in this experiment. In one group, the males were castrated, so they wouldn’t produce natural testosterone. These males were each given a small implant that released synthetic testosterone designed to have the same effects on the body as natural testosterone. In the next group, males went through a procedure to mimic castration, but were effectively left intact, and implanted with an empty implant. These males still produced natural testosterone. In the final group, males were castrated and each one was given an empty implant, so they did not have testosterone in their bodies.

Wild anoles were recaptured after two months. The researchers measured the size and color of the dewlap, how much fat was stored (which provided the researchers with an estimate of energetic state), and body condition. They took the same measurements in the lab population.

There were clear differences between the males that had testosterone (both natural and synthetic) and males that did not have testosterone. Castrated males had smaller dewlaps compared to intact males and testosterone-treated males in both the field and lab populations. Dewlap size of testosterone-treated males was similar to that of intact males in the wild population, but in the lab population, testosterone-treated males had larger dewlaps than intact males.

Castrated males in the wild population had brighter, more saturated dewlap coloration than testosterone-treated males and intact males. In the lab population, dewlap coloration did not differ among the treatments.

In the wild population, castrated males had higher body fat mass than intact males and testosterone-treated males. Wild testosterone-treated males were similar in body fat to intact males. Castrated males in the lab population also had higher body fat mass than intact males and testosterone-treated males.

The researchers also looked to see if either fat mass or body condition were correlated with dewlap size or color within each treatment group. None of these variables were correlated with one another.

Overall, while dewlap expression was not dependent on an individual’s energetic state, both energetics and dewlap expression were directly influenced by a common hormone: testosterone.