Day’s Edge Productions has produced a great new video about how two species with seemingly identical dewlaps manage to coexist. Manuel Leal explains what’s really going on.

This video originally appeared in bioGraphic, an online magazine from the California Academy of Sciences that features beautiful and surprising stories about nature and sustainability. 

What is bioGraphic, you ask? Here’s what it’s webpage says:

A multimedia magazine powered by the California Academy of Sciences, bioGraphic was created to showcase both the wonder of nature and the most promising approaches to sustaining life on Earth. We hope our stories will spark conversations, shift perspectives, and inspire new ideas, helping not only to shed new light on our planet’s most pressing environmental challenges, but also—ultimately—to solve them.

Through an ever-evolving array of storytelling tools and techniques, we will introduce you to some of the world’s most intriguing creatures and inspiring people. We’ll also transport you to faraway places, enabling you to experience what it’s like to be there and what’s at stake for those involved. Along the way, we’ll take a critical look at the environmental issues that pose the greatest threats to our future—and the most promising ideas for addressing them.

So please come along—and come back often—as we travel the globe in search of stories that inspire both awe and hope for a more sustainable future.

Kristin Winchell talks about her studies on urban anole evolution on an interview on PRI.

Photo by Ariel Kahrl

Sexual dimorphism, or differences in size or appearance between the sexes, was used by Darwin to explain sexual selection in On the Origin of Species. Interestingly, sexually dimorphic traits, like antlers in deer or showy feathers in peacocks, often do not present themselves until the animals are reproductively mature. Juveniles are often sexually monomorphic, or relatively similar in appearance. Few studies have investigated how sexual antagonism, when different sexes have different optimal strategies, of these traits may develop in the wild over the course of the animal’s maturation. So Aaron Reedy from the Bob Cox Lab at the University of Virginia decided to tackle this question with brown anoles (Anolis sagrei) in Florida.

After tracking thousands of lizards for several generations, Aaron found that selection changed throughout an animal’s life. Adult lizards had selection pressure for large males and small females in one year, but reversed the next, which was surprising, but in both cases was still sexual antagonism. For juveniles, on the other hand, larger body sizes were better regardless of sex. This is an example of sexually concordant selection, where both sexes have similar optimal strategies. He also found that there was selection pressure on the dewlap (an important ornament of anoles in courtship displays) to be smaller in one year, but then reversing the next so that males with larger dewlaps had better chances of survival. This year-to-year variation in selection is interesting and hopefully we’ll learn more from this system in the future.

I’ve recently learned that famous nature micro-photographer Piotr Naskrecki observed an aquatic anole catching prey underwater. Here’s what he had to say on his blog, The Smaller Majority:

The other aquatic iguana

Buy ’em here, use this code: WINTERTREATS

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.

Jeanel Georges with her poster at SICB.

The beautiful island of Dominica used to be home to only one anole (Anolis oculatus), but about 20 years ago, the Puerto Rican crested anole (Anolis cristatellus) showed up. Jeanel Georges, a graduate student in Matt Watson’s lab at Midwestern State University in Wichita Falls, Texas who is originally from Dominica, noticed that while A. oculatus occurs in all the ecological zones of the island, A. cristatellus is absent from the cooler, wetter uplands. With an international group of collaborators, Jeanel examined the thermal habitat use, sprint speed, and bite force of both species to determine what may limit the spread of A. cristatellus across the island.

At a lowland site where the two species co-occur, both species had higher body temperatures that the operative temperatures randomly available in the environment. In the much cooler upland site, A. oculatus had much higher body temperatures than the operative models, but these body temperatures were cooler than that species experiences in the lowland site. Jeanel also found that the two species had stronger bite forces and higher sprint speeds in the lowland site than A. oculatus had in the upland site. These data suggest that A. cristatellus and A. oculatus are partitioning the thermal environment of Dominica, and as climate change alters the temperatures available to lizards on the island, the interactions between these two species may change.

Austin Hulbert with his poster at SICB 2017.

This post was written by Brittney Ivanov, research technician in Michele Johnson’s lab at Trinity University.

Austin Hulbert, an undergraduate in Dan Warner’s lab at Auburn University, presented a poster on the behavior of brown anoles (Anolis sagrei) in a novel environment: a few very hot greenhouses in Auburn, Alabama. Brown anoles are an invasive species, most notably in Florida, but some populations have been found farther north in states including Louisiana, Alabama, Mississippi, and Georgia. As ectotherms migrate to higher latitudes, they often have to deal with different thermal environments and must alter their behaviors accordingly. Austin was interested in determining the activity patterns of a population of brown anoles inhabiting a group of greenhouses in Alabama.

During the summer he found that temperatures inside the greenhouses were consistently higher than those outside. Temperatures drastically increased each morning, up to peak temperatures between 11am and 3pm (on average, 45°C inside the greenhouse and 37°C outside). In the evenings, the temperatures again cooled. Austin surveyed the greenhouses and the surrounding areas for anoles during the morning, peak, and evening hours and determined the type of substrate each individual was using (i.e. brick or concrete, ground, metal, or wood). On average, brown anoles were more abundant inside the greenhouses than outside during the morning and peak times. He also found that more of the brown anoles perched on wooden substrate in the morning and evening. During peak hours more lizards perched on the ground. Because temperatures are often cooler closer to the ground, the lizards may be altering their behavior to deal with the extreme heat in the greenhouses during the hottest part of the day. While the visual survey focused on lizards perched in the open areas visible to the surveyor, there may have been individuals hiding under undisturbed objects as a means to keep cool during peak hours. In the future, Austin would like to compare the thermal tolerance of this group of brown anoles to those of populations in Florida to determine if inhabiting these greenhouses has resulted in adaptions to tolerate their more extreme temperatures.