Author: mjohnson216 Page 3 of 5

Evolution 2016: “Lightning” Strikes Three Times on Anoles in Afternoon Session: Character Displacement, Performance Trade-Offs and Opsin Evolution Matching Dewlap Color in Anoles

On June 19, 2016

In this afternoon’s round of lightning talks, anoles were the focus of three fantastic (but short!) presentations on adaptation. It’s not easy to summarize a whole project in five minutes, but that’s just what these three speakers did, and each left me wanting to know more!

First, James Boyko, a Masters student working with Luke Mahler at the University of Toronto, described his work on morphological evolution in Lesser Antillean anoles. When similar species compete over a shared resource, there are two possible outcomes: extinction or divergence (i.e., character displacement). Lesser Antillean anoles are an excellent system in which to study the role of character displacement, as these islands all have either one medium-sized species, or one large and one small species. Further, the species on these islands represent two colonization events – one from the north, and one from the south. James first confirmed the classic pattern on body size evolution, finding that a three peak Ornstein-Uhlenbeck model (i.e., one that predicted large and small lizards on two-species islands, and medium lizards on single-species islands) best fit the observed data (consistent with Butler and King 2004). But when he analyzed 20 other ecologically-significant morphological traits, this three peak model did not predict trait evolution better than a model based on random chance, although the northern and southern clades significantly differed in these morphologies. In summary, to understand the evolution of Lesser Antillean anoles: body size matters, as evolution in body size is clearly an important factor to reduce inter-species competition, but lineage matters too, as body shape was predicted by ancestry.

Next came Ann Cespedes, a Ph.D. student with Simon Lailvaux at the University of New Orleans. Ann is studying functional trade-offs in green anoles (Anolis carolinensis), focusing on relationships between fitness and performance. Many studies have searched for these trade-offs in the past, and some have found them, but others haven’t. Why the discrepancies? Ann proposed that previous studies haven’t always considered sex differences in functional trade-offs, that measuring only two traits (one associated with fitness and one with performance) may not reveal real trade-offs, and that differences in individual quality are often ignored. To consider all of these factors, she measured a suite of performance and morphological traits in 60 male and 60 female green anoles. Illustrating the limitations of examining raw data on sprint speed and endurance, Ann found no suggestion of the predicted trade-off between these traits. But when using a composite measure of all performance measures (sprint speed, bite force, clinging ability, exertion, endurance, jumping ability, and climbing ability) as a control for individual quality, the trade-off between speed and endurance became clear. Males and females also differed in their speed-endurance trade-offs, as body size predicted performance in different traits between the sexes, and body shape predicted male but not female performance. So performance trade-offs do exist, but you have to know how to look for them!

To conclude the session, Alexander Stubbs, a graduate student in Jimmy McGuire’s lab at the University of California, Berkeley, described the differences between opsin gene expression in two Cayman Island anoles: Anolis sagrei (a species with a red dewlap that reflects long wavelength radiation) and Anolis conspersus (a species with a blue dewlap that reflects short wavelength radiation). Alexander proposed that these different dewlap colors might provide different selective pressures on opsins in the two species to allow better color discrimination and angular resolution. Using RNAseq to measure mRNA in the eyes of six males of each species collected at solar noon or at sunset, the results were exciting. As predicted, Anolis conspersus had higher expression of opsins that increase visual sensitivity to UV, blue, and green wavelengths, and Anolis sagrei had higher expression of opsins that increase long wavelength sensitivity. Alexander also found that gene expression different substantially between noon and sunset, and further, there was surprisingly little variation in opsin expression between lizards, in stark contrast to the wildly varying opsin expression observed in humans.

SICB 2016: Urbanization, Predation, and Foraging

By mjohnson216

On January 14, 2016

In New Research

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

Zac at SICB in Portland

Urbanization is a phenomenon that comes with human population growth and development worldwide. For humans, urbanization can be positive, providing jobs, housing, and consequentially more growth. However, urbanization can have drastic, negative effects on local animal species, forcing them to respond to a rapidly changing environment. Zac Chejanovski, a Ph.D. student in Jason Kolbe’s lab at the University of Rhode Island, studied this phenomenon in the foraging behavior in one anole species: the invasive brown anole, Anolis sagrei.

Anolis sagrei are found across a range of habitats with varying degrees of urbanization. Zac predicted that an anole’s perceived risk during foraging is related to the degree of urbanization in its habitat. To test this, he set up plates of mealworms near wild A. sagrei and determined their latency to feed. He found that those lizards living in the most natural forested habitat had the shortest latency to feed, whereas those from suburban and urban habitats were much slower to take advantage of foraging opportunities. These results provide support for the idea that an anole’s perceived risk during foraging is related to habitat urbanization.

Taking this a step further, Zac decided to consider the effects of a known anole predator, Leiocephalus carinatus (curly tail lizards), which inhabits some urban environments, on foraging behavior. He wanted to know if A. sagrei foraging behaviors differed between urban habitats with curly tails and those without. To test this prediction, in both habitats Zac determined the amount of time that A. sagrei naturally spent on the ground (i.e., ground use), their latency to feed, and their ground use when presented with a mealworm. He found that in urban habitats where curly tails are present, A. sagrei’s ground use increased when curly tail activity decreased. In addition, during the times when curly tails are least active, Zac found no differences in latency to feed or ground use between A. sagrei from urban habitats with and without curly tails. Together, these results suggest that A. sagrei are adjusting their foraging behaviors in response to not only urbanization, but predation risk as well.

SICB 2016: Modeling Color Vision in Anoles

By mjohnson216

On January 11, 2016

In All Posts

Leo Fleishman of Union College

Anoles are highly visual animals, and there’s no display more visual than the extension of a dewlap. To understand how anoles use their colorful dewlaps to communicate, we must understand how anoles perceive color. Leo Fleishman of Union College has set out to do just that.

In his standing-room-only talk at SICB, Leo explained the need for a species’ dewlap to be easily distinguishable both from the dewlaps of other sympatric species, and from the background colors in the habitat. He described how his team quantifies dewlap color and natural habitat light conditions to determine how colors are differentiated by the anole visual system. One general finding that has emerged from these studies is that species in dark habitats have evolved lighter dewlaps, and those in brighter habitats have evolved darker dewlaps.

How do these things work?

Leo also described how to differentiate anole visual signals using a color tetrahedron of anole perceptual color space. This tetrahedron is defined by the sensitivity of the four types of photoreceptors in anoles – cones that detect long wavelength, medium wavelength, short wavelength, and ultraviolet light. By plotting the spectral radiance of particular signals (for example, the dewlaps of two species) in the tetrahedron, you can determine how distinct two (or more) signals are in anole visual space. Further, this modeling approach allows us to determine the visibility of any dewlap in any environment!

Leo concluded his talk by describing one particularly cool way an anole can distinguish its dewlap in a low-light habitat: the translucent dewlaps of some species that seem to almost glow in deeply shaded forests. You can read more about these glowing dewlaps in a recent Open Access paper published in Functional Ecology by Fleishman and colleagues.

SICB 2016: Trade-offs between Growth and Metabolism in Brown Anoles

By mjohnson216

On January 11, 2016

In All Posts

John David Curlis presenting his poster in Portland.

Sexual size dimorphism can vary dramatically among populations, a pattern that may be due to sex-specific trade-offs between growth and maintenance. John David Curlis, a Masters student in Christian Cox’s lab at Georgia Southern and a former undergrad in Bob Cox’s lab at the University of Virginia, tested this hypothesis in two populations of brown anoles (Anolis sagrei) in the Bahamas. These two populations – one from Exuma, one from Eleuthera – differ in male but not female body size, and so they also differ in SSD. John David and the Drs. Cox thus predicted that the population of brown anoles from Exuma with faster male growth would have lower male resting metabolic rates than the population from Eleuthera with slower male growth. Since females on the two islands have similar growth rates, they predicted that females would have similar resting metabolic rates.

The team first found that the average metabolic rate was higher for males on Eleuthera than Exuma in both day and night, but this difference was not significant. As predicted, they did not find a difference between females of the two populations. They next tested whether metabolic rate differed between the populations at different temperatures, and found that Eleuthera males had higher metabolic rates at 25°C and 30°C, but not at 35°C. Again, females didn’t differ in metabolic rate at any temperature.

Altogether, the results of this study suggest that population differences in body size may be related to population differences in the allocation of energy between growth and metabolism, and interestingly, that these differences can be sex-specific.

SICB 2016: Lizard Sprint Speed is Limited by Muscle Twitch Speed

By mjohnson216

On January 5, 2016

In New Research

SICB is off to a very anole-y start in Portland! There have been anole-focused talks and posters all day, and your intrepid team of AA reporters are on the scene.

At Monday’s poster session, Noel Parks (an undergraduate at Brown University working with Chris Anderson and Thomas Roberts) presented her research on muscle contraction and sprint kinematics in Anolis sagrei and A. cristatellus. The team performed laboratory sprint trials with the two species at a range of inclines, and then using muscle tissues from the same lizards used in the trials, they measured how fast the M. ambiens pars ventralis (a hindlimb muscle critical for locomotion) can contract and relax after stimulation, a measure they call muscle twitch time.

Noel Parks and her poster at SICB 2016.

For both species, Noel and her colleagues found that stance time (the amount of time a foot is in contact with the ground) and swing time (the amount of time the limb is moving forward) are limited by the muscle twitch time. Thus, muscle twitch time may constrain the sprint speed of these animals. Further, at steeper inclines, stance and swing times more closely approached muscle twitch time. The two species differed in these speeds, however, as A. sagrei had faster twitch, stance, and swing times than A. cristatellus.

This work gives us another interesting piece of the puzzle in the larger story of anole locomotor performance!

Shipping Live Lizards via Cargo from the Dominican Republic

By mjohnson216

On July 14, 2015

In Notes from the Field, Research Methods

Assuming you can’t get your lizards to fly themselves to your lab, you might want to read this information on how to transport them home. Photo from http://www.deviantart.com/morelikethis/27371609

After years of transporting live anoles from the Caribbean to my lab in the United States in my checked luggage, this summer in the Dominican Republic, a Delta Airlines agent refused to accept our cooler full of lizards as luggage for our plane. After pursuing every avenue we could think of, it became clear that our only remaining option was to ship the lizards as cargo. We spent several days working out this process, and after making a number of mistakes, we finally arrived at a relatively smooth procedure. To prevent others from having to learn these steps on their own, if such a situation arises for other researchers, we’ve written out the steps that worked for us below. The details provided are for the airport in Santo Domingo, but this general approach may be helpful in other locations as well. (And, if you find yourself in the Dominican Republic in the near future, I’d be happy to give you the contact information for all of the folks listed below.)

SICB 2015: Color and Stress in Green Anoles

By mjohnson216

On January 9, 2015

In Education and Anoles, New Research

Spencer Hudson presenting his poster at SICB.

When you tell someone that you study anoles, often one of the first questions they’ll ask is why these lizards change color. While it’s a complicated phenomenon, we do know that anole color can indicate both social dominance and stress. In a poster presented on Tuesday at SICB, Spencer Hudson, an undergraduate working with Travis Wilcoxen at Millikin University in Decatur, Illinois, considered whether habituation in green anoles can mediate the effects of social and handling stress (measured via fecal corticosterone, or CORT), and how stress is associated with color. Spencer found that in comparison to a control group, male lizards that experienced human handling and social interactions with other males had higher CORT levels, and they were more likely to turn brown during experimental trials. However, he did not find evidence that habituation lowered CORT or influenced lizard color. Spencer and his colleagues suggest that acute stress (experienced during human handling) and chronic stress (experienced over the course of the three-week experiment) may have different effects on lizard color.

Impressively, Spencer designed and conducted this experiment all within a one-semester undergraduate Animal Behavior class at Millikin!

SICB 2015: The Mechanics of Arboreal Locomotion

By mjohnson216

On January 9, 2015

In New Research

Anolis equestris. Photo courtesy of Day’s Edge Productions.

The ability to move through complex arboreal habitats is critical to anoles, yet we know very little about the physiological mechanisms that underlie arboreal locomotion. Kathleen Foster, a graduate student in Tim Higham’s lab at UC-Riverside, presented an outstanding talk at SICB this week on the kinematics of locomotion in Anolis equestris. (Yep, Kathleen gave both a poster and a talk at this meeting!)

The relationship between the force a muscle can produce and the length of that muscle determines how force is generated at different positions of a limb – at different joint angles, the muscle will have a different length. But, this is extremely difficult to study in anoles, as standard surgical techniques aren’t possible in such small muscles. Kathleen is focusing on the muscles of the hindlimb, and she first determined that tendon strain did not contribute to the force-length relationship in these muscles. This result indicated that in vivo measures of muscle length should provide relevant information on limb kinematics. Next, she addressed how muscle function changes as lizards move on different substrates, using the gastrocnemius (a muscle in the “calf” of the hindlimb). Her preliminary data showed that this muscle is more active on a broad, flat perch than a small, narrow perch, that the active length of the gastrocnemius is more optimal on a flat perch, and that the maximum force generated by the gastrocnemius is greater on a flat perch. Together, these results indicate that the gastrocnemius contributes more to locomotor propulsion on a flat perch than a small perch.

And, because Kathleen has shown that tendon strain doesn’t significantly contribute to differences in muscle length in lizards, she can now study smaller species. This will allow her to examine the physiological differences underlying locomotor adaptations among ecomorphs!

SICB 2015: Anoles Alter Behavior Based on Social Status

By mjohnson216

On January 7, 2015

In New Research

Photograph of Deep Shukla, courtesy of neuroscience.gsu.edu.

What effect does social rank have on display rate in Anolis carolinensis? Can individual display patterns predict social status? Deep Shukla, a graduate student at Georgia State University in Walt Wilczynski’s lab, addressed these questions during Tuesday’s poster session at SICB 2015. Green anoles often form dominance hierarchies in conditions with limited resources (such as those in captivity). Deep predicted that competition for these resources might also cause behavioral variation in display use between dominant and subordinate anoles. Using a mirror to induce display behavior and a female to induce courtship behavior, Deep counted the number of pushups performed by size-matched male anoles in isolation. He then housed two males together for 7 days to allow males to establish a dominance hierarchy within the cage. After the weeklong cohabitation, Deep again measured display frequency levels for each male.

In the baseline trials Deep found that the males who later were identified as dominant and subordinate males did not differ in the frequency of aggressive or copulatory displays. After cohabitation, display use frequency declined for both dominant and subordinate lizards overall, but dominant lizards showed higher levels of aggression relative to subordinates. Deep also found that aggressive behavior was correlated with copulatory display before cohabitation; however, this result disappeared after cohabitation. These results suggest that dominance hierarchies in anoles can alter display behavior use based on social rank! This is exciting because it means that dominance hierarchies may be established and maintained in complex ways. Deep is interested in exploring these relationships further by measuring brain metabolic activity and morphology before and after the establishment of dominance hierarchies. Given his preliminary data, it seems likely that there will be interesting differences in the brain that accompany this suite of behavioral changes!

Note: This post was written by Bonnie Kircher, a graduate student studying anole development in Marty Cohn’s lab at the University of Florida.

SICB 2015: Genetics and Geography: Patterns of Brown Anole Diversification

By mjohnson216

On January 7, 2015

In New Research

Anolis sagrei, the almost-ubiquitous brown anole, has spread across a broad geographical range that spans most of the Caribbean. The populations across this range, however, vary extensively in morphological traits. Graham Reynolds, currently a postdoc working with Liam Revell and Jonathan Losos, summarized this morphological variation and described a large-scale phylogeographic study of population differentiation in brown anoles in a talk at SICB on Tuesday.

The context of Graham’s study arose from Lister’s classic 1976 paper showing variation in the number of toe pad lamellae in brown anole populations from different Caribbean islands. Lister found that average lamellae number corresponded to average perch height. More recently, Veronica Gomez-Pourroy’s masters thesis work showed that brown anole morphology varies across mainland Central America, the Swan Islands of Honduras, and the Caribbean.

Graham’s genetic work expanded on the results of Kolbe et al. (2004) and included samples collected by a large number of collaborators working in 95 localities throughout the Caribbean Basin. Using multilocus nuclear and mitochondrial data, Graham found a large split between the Eastern and Western Cuban clades of brown anoles. Populations from the Bahamas clustered with the Western Cuban clade, and populations from the Swan Islands and Central America were most related to populations from the southern populations of the Eastern Cuban clade.

Graham’s overall aim is to integrate morphology, behavior, and genetics from local to regional scales. Anoles seem to be the perfect group with which to tackle this goal!

A photo of Graham Reynolds holding a Hispaniolan boa. Photo from his website.