All posts by medhavi

SICB 2017: Testosterone Influences Dewlap Expression and Energetics

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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.

SICB 2017: Can We Measure Heart Rates of Anole Embryos?

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Above: Dani Douglas presenting on her research on measuring heart rates of brown anole eggs at the annual Society for Integrative and Comparative Biology Meeting in New Orleans, Louisiana.

Heart rate can tell us a lot about how an animal’s physiology is influenced by environmental conditions. Even embryos can provide valuable heart rate information. Scientists have used the Buddy® system, a digital egg heart rate monitor, to measure heart rate in large eggs, such as those from chickens or iguanas. But can the Buddy® system detect heart rate measurements from much smaller eggs?

Cassie Guiffre, Austin Hulbert, and Dani Douglas, students at Auburn University working with PI Dr. Dan Warner, took heart rate measurements from brown anole (Anolis sagrei) eggs using the Buddy® system.

Compared to a chicken egg, a brown anole egg is tiny – smaller than a quarter. Guiffre, Hulbert, and Douglas kept the anole eggs in an incubator that varied temperature over the course of each day. At different points during the day, they removed eggs from the incubator to measure heart rate with the Buddy®.

The students were elated to find that the Buddy® system could reliably measure heart rate in those small anole eggs. This finding is especially exciting because the Buddy® system is non-invasive, so scientists can measure heart rate over the development of the eggs.

They also found that anole egg heart rates were positively correlated with temperature fluctuation. Anole egg heart rate was not related to the age of the egg.

All research comes with its own set of challenges. When each anole egg is removed from the incubator, its temperature begins to go down immediately. The students needed to measure heart rate quickly to avoid confounding effects of cooling, which can be tricky.

Challenges aside, it is promising thatthe students in the Warner lab ave confirmed that heart rate can be measured in tiny anole eggs.

SICB 2017: Big Anoles in the City: Drivers of Body Size in Urban Brown Anoles

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Urban environments are spreading and can influence the biotic and abiotic components of an ecosystem. Brown anoles (Anolis sagrei) that live in urban environments are larger in body size than their counterparts that reside in more natural areas. Body size is important for brown anoles because larger individuals can run faster, eat larger prey, and are more competitive. But what’s driving the variation in body size across urban to natural environments? Zac Chejanovski, a PhD student at the University of Rhode Island sought to answer this question.

Chejanovski did his research in south Florida at 38 sites along an urban to natural gradient. He measured food availability, abundance of conspecifics, and abundance of a known predator of anoles, the curly-tailed lizard. He also captured 15 male and 15 female anoles and measured body size, body temperature, and the thermal environment.

Curly-tailed lizard abundance had a strong positive relationship with body size for both male and female anoles. There was a weak positive relationship between the thermal environment and body size for males, but not females. Neither food availability nor abundance of conspecifics were related to body size. The findings of this research suggest that predation pressure from curly-tailed lizards might be one factor driving selection on body size variation in brown anoles.