Emily Watts with her poster in NOLA at SICB 2017.

Great new aggression work from the McGlothlin lab! Emily Watts, an undergraduate student, presented a poster on Saturday about differences in aggression between island populations of A. sagrei.

Previously, the McGlothlin lab quantified aggression of brown anoles from Eleuthera, Exuma, North Andros, and San Salvador in the Bahamas. They found that individuals from Exuma and North Andros were more aggressive than from Eleuthra and San Salvador. Emily wanted to know if these population-level differences were a result of genetics or of the environment.

To test this, she bred lizards from Eleuthra and Exuma in the lab using a full cross design and raised the offspring in a common garden environment. When the males were one year old, Emily used enclosure trials to quantify aggression for each individual. The results were not what she expected. She found that aggression was independent from where a lizard’s parent came from, but was instead influenced by the environment.

Next, Emily will be testing offspring from the North Andros – San Salvador crosses they also performed. Additionally, because aggression was not repeatable for individuals, Emily will be testing each male again against a mirror to quantify individual aggression independent of partner aggression.

Thanks for sharing, Emily! We look forward to next year’s presentation.

Sukalia Miller with her poster at SICB.

This post was written by Miguel Angel Webber, an undergraduate in Michele Johnson’s lab at Trinity University.

An animal’s position in a social hierarchy can influence many aspects of its behavior. In the green anole (Anolis carolinensis), a growing body of literature indicates that dominant males behave differently than subordinate males, and that these behavioral differences may be present even prior to the establishment of a dominance hierarchy. Sukalia Miller, a recent undergraduate in Walt Wilczynski’s lab at Georgia State University, designed an experiment to determine whether subordinate and dominant males differed in their rates of courtship, aggression, and exploratory behavior.

After taking baseline measures of behavior, size-matched green anoles were paired and allowed to establish dominance relationships over the course of six days. Following this pairing, each lizard was then tested again to determine post-pairing measures of behavior. Miller found that subordinate males did not differ from dominant males in their rates of aggression (as simulated in a mirror test) or courtship (tested by placing a female in the habitat) prior to pairing, but that bouts of aggression and courtship practically disappeared in the subordinate group after pairing. Additionally, Miller found that there was a trend in the dominant lizards, such that individuals with higher rates of pre-pairing aggression had higher rates of aggression post-pairing. However, no such relationship was found between pre- and post-pairing rates of courtship in either the dominant or subordinate group, and no Miller observed no differences in exploratory behavior between either group of lizards.

These results suggest that the influence of social status on behavior may be limited to social behaviors in green anoles, and furthermore, that these behavioral differences may not be detectable prior to the establishment of a dominant-subordinate hierarchy.

Maria Jaramillo with her poster, doing her best anole impersonation.

Behavior can be extremely variable, even within a species. To control for this inherent variability while assessing individual responses to a visual stimulus, some researchers have begun using videos in their experiments. Maria Jaramillo, an undergraduate student in Michele Johnson’s lab, is curious about how anoles process visual information and if videos and live encounters are processed similarly in the brain. On Saturday, Maria provided us with an update of her work.

For this experiment, Maria used 40 adult male A. carolinensis which were exposed to one of four treatments for 15 minutes: 1) another live anole, free to display; 2) a looped video of an anole, which displayed for about 30 seconds, waited 15 seconds, then displayed again; 3) a scrambled version of the previous video; 4) or a control video of a lizard perch. She recorded the behavior of these lizards, then sacrificed them in order to collect their brains.

Maria found that the lizards paid close attention to the live anole, the video of the anole, and the scrambled anole video, but significantly less attention to the control video. Interestingly, though, males displayed significantly less to the scrambled and control videos than to the live anole and the normal video.

Next, Maria will use immunocytochemistry to quantify c-fos+ neurons in five brain regions associated with visual processing and the social behavior network. c-fos is an immediate early gene that is transcribed when neurons are activated, and c-fos+ neurons were likely stimulated in response to the visual stimuli Maria presented. She will then use the ratio of ­c-fos+ neurons to total number of neurons in that brain region to quantify neural activity in the five brain regions and see how these differ between stimulus treatments.

This is really exciting work and we can’t wait to see the end result!

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.

This post was written by Miguel Angel Webber, an undergraduate in Michele Johnson’s lab at Trinity University.

Samantha Adams presenting at SICB.

The parietal eye, a photosensitive organ located on top of lizards’ heads, has long been thought to play an important role in regulating lizards’ circadian rhythm and body temperature. The eye detects UVB rays, mediating the release of melatonin from the pineal gland and evoking a behavioral response. Samantha Adams, an undergraduate at Marosh Furimsky’s lab at Westminster College, PA, conducted a study on bearded dragons (Pogona vitticeps) and green anoles (Anolis carolinensis) to examine the effects of masking their parietal eye on their thermoregulatory behavior. Adams took individuals from each species and set up a testing arena, placing a UV-B light-only source and an infrared heat-only source on opposite sides. She then tracked the amount of time each lizard spent under either lamp, doing so before masking the parietal eye, while the eye was painted with black non-toxic paint, and again after uncovering it.

Adams found that bearded dragons rely heavily on the eye for thermoregulation – while lizards ordinarily spend less than 20% of their time basking underneath the heat source, lizards with their parietal eye masked spent the vast majority of their time under the heat lamp. Additionally, all of her bearded dragons experienced erratic locomotion in the day post-masking, running so frequently from side to side of the cage that she had trouble characterizing the lizard’s lamp preference. Once the black paint was removed, lizards took one to two weeks to resume ordinary behavioral patterns. However, she found that the green anoles in her study seemed unaffected by the experimental manipulations; lamp preference was unchanged by covering the parietal eye, and anoles spent roughly 25% of their time under the heat lamp in both the control and experimental treatments. The anoles displayed none of the erratic locomotor patterns Adams found in the bearded dragons, and other than a qualitative account of more time spent being brown, the lizards seemed unperturbed by the black paint on their parietal eye.

Adams’ results shine a new light on the parietal eye, long thought to be a structure essential to all lizards that possess it, as a potentially vestigial structure in green anoles. Future work is necessary to understand any other roles the eye could serve in anoles, but the stark difference with bearded dragons in this study helps illuminate the wild evolutionary path of our favorite lizards.

Hello from unexpectedly cold New Orleans! Our coverage of SICB 2017 continues and we hope you will enjoy the increased posting over the next few days.

On Friday, David Delaney presented more data from his Master’s thesis from Dan Warner’s lab further exploring how adult and juvenile A. sagrei interact. Previously David showed that the presence of adults did not affect microhabitat use, but that high densities of adult males decreased survival in juveniles, especially in smaller lizards.

This year David presented intriguing data suggesting that the presence of adult males influenced how juveniles sat on their perches. He found that the presence of adult males alter both horizontal and vertical orientation of juveniles. When one male is present, juveniles increase horizontal orientation over time, but if three males are present, juveniles face upwards more than when no or only one male is present. Additionally, they also face the trunk of the tree more than away from the tree when they are horizontal and adults are present. Because of the chance of juvenile saurophagy, David suggests this helps juveniles to monitor where the adult males are to prevent being eaten.

Check back often to read about more great research being presented at SICB 2017!

• • The Scientist »
  • January 2017 Issue »
  • Notebook

Caribbean Anoles Function as Model Organisms for Evolutionary Dynamics

The small lizards adapted to unique niches among dozens of isles.

By Amber Dance | January 1, 2017

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NOTICE ME!: A male Anolis stratulus (barred anole) extending his dewlap in Puerto RicoPHOTO BY MICHELE JOHNSON

It’s not easy to snare a lizard. Evolutionary biologist Michele Johnson affixes a noose made of dental floss to a telescopic fishing rod to reach into the bushes and tree canopies where Caribbean anoles live. By the end of the summer field season, her students from Trinity University in San Antonio, Texas, develop a knack for it. “We almost always catch our lizards,” says Johnson.

She doesn’t just collect field measurements and observations; she’s taken 30 different species of anoles back to her lab to analyze their physiology. Anoles have become a favorite model for evolutionary biologists because of their extraordinary diversity—there are more than 400 species in genus Anolis—and because of how they originally populated the Caribbean islands. The relative scarcity of mammals, snakes, or birds on the islands left many niches open for the lizards to occupy.

As anoles—which also inhabit Central and South America—reached individual islands, their populations diversified into island-specific forms that occupy certain niches. For example, each of the four largest islands in the Greater Antilles (Hispaniola, Cuba, Puerto Rico, and Jamaica) hosts one or more species that are green lizards hanging out in the lower canopies of trees, and another group of short-limbed, slow-moving reptiles that perch on twigs. These are two of the six “ecomorphs” that scientists who study Caribbean anole species have defined. To be considered an ecomorph, a set of habitat specialists must exist on more than one island, though the species in each group differ between islands. And yet, other anole species belong to no particular ecomorph class.

Caribbean anoles offer scientists a sort of “natural experiment,” explains Luke Mahler, an evolutionary biologist and herpetologist at the University of Toronto. Each isle, with similar environments, acts as a replicate for how anoles underwent convergent evolution into ecomorphs. As a result, evolutionary studies of anoles have flourished in the past couple of decades—think Darwin’s finches, but scalier.

“They really are a good model system for lots of questions, from very small-scale molecular work all the way up to adaptive radiation,” says Jerry Husak, a physiologist at the University of St. Thomas in St. Paul, Minnesota.

The basic anole ecomorphs go way back in evolutionary history, found Jonathan Losos, an evolutionary ecologist at Harvard University. Emma Sherratt, now at Australian National University in Canberra, got a hold of 20 fossil anoles while a postdoc in Losos’s lab. The fossils dated back 15 million to 20 million years, when the lizards were preserved in amber on the island of Hispaniola. Some were in museums, others in private collections. Using CT scans, the Losos team examined anatomy to confidently assign these fossils to four of today’s ecomorphs; a couple other fossils might be part of a fifth (PNAS, 112:9961-66, 2015). “At least several of the habitat specialist types already existed,” concludes Losos.

Despite the countless hours biologists have spent studying Caribbean anoles, the genus seems to have plenty of surprises still in store. In addition to her ongoing studies of physiology and behavior in diverse anole species, Johnson has recently focused on how her local Texan anole, Anolis carolinensis, determines dominance. A. carolinensis, like many other anole species, adopts a strict mating hierarchy in captivity, with males battling each other for access to prime habitat and to females. In the field, the hierarchy is more complicated—a lizard defending his own territory is more likely to win a fight, she thinks. She figured the biggest males would also be more likely to triumph, either in the lab or the field, and thus achieve larger territory and more females to court.

In order to correlate body characteristics and behaviors with dominance, Johnson’s group set up a sort of lizard fight club, pitting anoles against each other in one-on-one cage matches, with a single perch to battle over. Winners tended to execute more visual displays, performing push-ups and head-bobs and expanding the showy throat skin known as a dewlap. They also chased and bit the losers, who tended to back away and to hide in a corner.

But larger anoles weren’t always the winners in captivity or in the field. “Body size doesn’t predict who wins these fights at all,” says Johnson. Instead, behaviors made a huge difference—the most aggressive lizards won their matches. A longer head also helped, perhaps because it looked to opponents like a serious biting weapon. In the field, animals with a wider head and powerful jaws occupied larger territories with more females present (Anim Behav, 118:65-74, 2016).

Body size still probably matters, Johnson says. She has not yet tested in field studies whether size might help an A. carolinensis male establish his territory or take over a vacated area. And at least in other anole species, bigger males sire more offspring.

Mahler also got a surprise from the anoles when, in 2010, he received an email from Miguel Landestoy, a Dominican naturalist who claimed he’d seen a new species. Mahler was initially skeptical. “Everybody thinks they’ve got a new species,” he says, yet “the Caribbean anoles are the best known anoles, by a long shot.”

Then Mahler opened Landestoy’s pictures. “Holy crap,” he said. “That doesn’t look like anything we’ve seen on Hispaniola.” The critter was huge, by anole standards—about a foot from nose to tail tip. It had short legs, a short tail, and a mottled greenish-gray pattern that suggested it could easily blend into a mossy or lichen-covered branch. “I bought the first cheap flight I could find,” recalls Mahler.

The other thing that struck Mahler about the new species—which he and his colleagues dubbed A. landestoyi—was that it looked similar to anoles found in Cuba. Their clade is called chamaeleonides for their creeping, chameleon-like movements and camouflage prowess. These particular kinds of anoles, scientists had assumed, were unique to Cuba. But here was another species, making its living in many of the same ways, on Hispaniola (Am Nat, 188:357-64, 2016). “This is an example of what might be a seventh ecomorph. . . . Evolution is more predictable than we have yet given it credit for,” says Johnson, who was not involved in the project.

“It’s amazing, in part, that anything new there could be found after all these years,” adds Losos, a coauthor on the study. “The age of discovery is not yet over.”