SICB 2016: Brown Anole Crest Formation

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Brown anole with and without crest shown at the whole-animal (left) and histological (right) level. Photo from Ademi and Rand poster.

If you’ve ever been around brown anoles, you know that the males can be pretty aggressive. Part of that aggression involves the enlargement of a crest along the neck and back. The crest is caused by fluid rapidly rushing into the tissue of the crest. How this works has been discussed here before, but Matt Rand’s research group at Carleton College continues to try to unravel what hormonal pathways are responsible for crest formation. Ademi and Rand used an experimental approach to discover what molecular receptors are activated to cause crest formation. Body-wide and local injection of a variety of chemicals and drugs gave some tantalizing clues as to how it works.

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Local injections to stimulate cAMP activity caused crest formation locally (top), whereas body-wide injection caused whole-crest formation (bottom). Photo from Ademi and Rand poster.

They found after several inhibitory and stimulatory drug manipulations that crest erection is likely stimulated by epinephrine acting on a Beta-2 like adrenergic receptor that stimulates cyclic AMP (cAMP) activity to cause vasodilation (enlarging of blood vessels) and fluid entrance into the crest. This activity that starts with the B2-adrenergic receptor is essentially the same function as that seen in mammalian circulatory systems, including us. They also stimulated cAMP activity without stimulating the B2-like adrenergic receptor and found similar results. You can see how dramatic the response was below, where they used local injection to cause crest formation only at the site of injection! The use of epinephrine binding to a B2-like adrenergic receptor as the molecule of communication makes the rapid time-course of crest formation make sense. There are still some unknown aspects as to how the vasodilation mechanistically causes the fluid release in the crest, but they are actively studying it.

SICB 2016: Blood Physiology across Elevational Gradients

Are anoles like sherpas? Photo from Reddit

When you’re used to living at low to moderate elevations, it can be challenging to visit high-altitude places. The declining partial pressure of oxygen at high altitude makes it difficult for your body to deliver the same amount of oxygen to tissues. This is why National Football League players often struggle to play in Denver (see playoffs next week!). However, organisms that live at high elevations, including humans, have evolved a number of ways to deal with living in such oxygen-challenged environments. We know less about whether the same aspects of the cardiovascular change in different organisms, even among relatively closely related species. Well, what better group of organisms to address such questions than anoles!

Virtually nobody reading this blog will be unfamiliar with the story of the Greater Antillean ecomorphs, and they are great to use for questions related to elevation and adaptations to deal with it. They live along steep elevational gradients within an island, and such gradients exist across islands. Although, the Caribbean anoles have been the subject of numerous studies that have shown convergent evolution in body size and shape, as well as locomotor performance and endocrine function, we know much less about how they deal with elevational challenges at the cardiovascular level.

Species studied and locations in the Dominican Republic. Photo from Webber et al.'s poster.

Species studied and locations in the Dominican Republic. Photo from Webber et al.’s poster.

Miguel Webber, an undergraduate in the laboratory of Michele Johnson at Trinity University, along with Brittney Ivanov, studied several blood physiology traits in 13 species across five ecomorphs in the Dominican Republic to determine whether elevation has been an important driving force in the evolution of oxygen delivery mechanisms. Although looking at an impressive number of traits that included hematocrit (the proportion of red blood cells), hemoglobin concentration, and red blood cell size, Miguel only found hemoglobin concentration to be positively related with elevation when looking across species.

One of the more interesting findings was that none of the blood physiology variables that Miguel measured were ecomorph specific. However, this makes sense because members of an ecomorph live across wide geographic areas and across elevational gradients. Physiological studies such as Miguel’s are offering interesting insights into how anoles have adapted to their environments and emphasizes that ecomorph membership does not determine everything.

SICB 2016: Intraspecific Variation and Divergence in Anolis conspersus

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Color variation of Anolis conspersus on Grand Cayman. Spotted individuals (left) are found in the west of the island and vermiculated ones (right) are found in the east.

Christopher Peterson, a masters student in the Fitzpatrick Lab at the University of Tennessee, studies color variation of Anolis conspersus on Grand Cayman. He found that lizards from eastern Grand Cayman are vermiculated and individuals from the west side are spotted. He hypothesized that color variation along the east-west axis might be due to climatic variation, habitat differences or population structure. He sampled multiple sites across the island and measured air temperature, relative humidity, degree of leaf coverage (shade), perch roughness and perch connectivity. Using a hierarchical Bayesian logistic regression, Christopher did not find correlations between body coloration and climatic variation or habitat differences. He found, however, that spotted individuals have significantly longer tails and vermiculated ones are larger (SVL) on average. Genome wide SNPs will reveal whether population structure can explain variation in coloration between eastern and western populations.

SICB 2016: Plasticity versus Adaptation in Tolerance for Dry Habitats

How does the environment an organism experiences during development influence its phenotype, and does the development environment prepare the organism for success in its habitat? Corey Cates, now a Ph.D. student in the Warner Lab at Auburn University, used Anolis lizards to answer this question at the SICB meeting in Portland, Oregon.

Because anoles do not practice parental care, once a female lays an egg, the embryo is at the mercy of the environment. Soil conditions, such as moisture and temperature, will influence how the embryo develops, and can have lasting impacts on that organism’s phenotype. Furthermore, a lizard is expected to have highest fitness when its phenotype matches its environment. Cates designed an experiment that manipulated the development environment, and examined the desiccation performance and survival of hatchlings, following them into adulthood. Anolis sagrei that hatched from eggs left in dry, poor-quality soil experienced lower desiccation rates than those from eggs in moist, high-quality soil. Building upon previously-presented work, Cates showed that adult desiccation tolerance was not heritable. After following adult lizards from each treatment released into both high and low-quality habitats for more than a year, Cates found that desiccation trends persisted, and that organisms from dry incubation conditions performed better in dry habitats than those incubated in more favorable conditions. This study is a fascinating look into how anoles may handle changing climates in the future.

SICB 2016: Adaptive Shifts in Anolis carolinensis Following the Polar Vortex

Shane Campbell-Staton gives his talk at SICB 2016.

Shane Campbell-Staton gives his talk at SICB 2016.

Climate change isn’t just leading to greater average environmental temperatures – it’s also leading to an increase in the frequency and severity of extreme weather events, such as heat waves and hurricanes. Of interest to Shane Campbell-Staton, a post-doctoral researcher in the Cheviron Lab and a recent graduate from the Losos Lab at Harvard, is understanding how the recent polar vortex in North America impacted the native green anole, Anolis carolinensis. The polar vortex of winter 2013/2014 set several records in snow fall and in all-time low temperatures in the south, and also led to severe weather in the midwest and east.

Shane found that, immediately following the polar vortex event, cold tolerance (CTmin) was significantly lower in lizards from southern Texas, as low as in lizards from much higher latitudes. He suggested that this result stems from differential survivorship during the event – lizards in south Texas that were more cold tolerant (i.e., had a lower CTmin) were more likely to survive the winter vortex  than less cold tolerant individuals. He then returned to south Texas a few months later and sampled both the survivors and their offspring and found that the decrease in CTmin persisted, indicating a potential evolutionary shift in cold tolerance. He put the final nail in the coffin by running a common garden experiment, where he demonstrated that, even when reared under common laboratory conditions, offspring exhibited cold tolerance similar to their parents, indicating high heritability in this trait and that the shift observed in nature was evolved rather than due to plasticity.

Shane then examined the response to the weather event at the genetic level by sequencing liver transcriptomes. Transcriptomes quantify patterns of gene expression levels for all genes regulated in a tissue; hence, by examining what genes are differentially expressed following cold stress, we can figure out the molecular underpinnings to cold adaptation and acclimation. He found that gene expression in survivors from the south closely resembled expression patterns in northern lizards, indicating a shared molecular pathway to cold tolerance adaptation in lizards from both habitats. The gene expression modules (or groups of genes) that exhibited a strong statistical association with CTmin variation were overrepresented for genes associated with oxidative phosphorylation. Oxygen consumption, which feeds oxidative phosphorylation, is directly related to CTmin: Animals that are more cold tolerant consume less oxygen during cooling. Hence, the expression differences in oxidative phosphorylation may pinpoint a proximate mechanism for cold tolerance adaptation.

You can learn more about Shane’s work on adaptation following the polar vortex in his recent Harvard Horizons talk.

SICB 2016: An Investigation Of Brain Lipid Composition Between Ecomorphs

Jake Stercula presents his poster at SICB 2016.

Jake Stercula presents his poster at SICB 2016.

*The following post was written by Chris Robinson, a Master’s student in Matt Gifford’s lab at the University of Central Arkansas.*

Both between and within ecomorphs, anoles can experience a wide range of temperature conditions. As ectotherms, anoles rely on external conditions to thermoregulate, and therefore species found in different environments may have evolved unique biochemical mechanisms to adapt to their respective environments.

Using both field and laboratory studies, Jake Stercula, an undergraduate working with Michele Johnson at Trinity, is investigating how membrane fluidity, which aids in cell function, of the brain is regulated by temperature and lipid composition. The saturated:unsaturated lipid composition ratio controls cell membrane fluidity, where a higher ratio provides less fluidity. Stercula and colleagues hypothesize that species within a thermal environment (warmer or cooler) will have more similar lipid ratios and fluidity than between thermal environments regardless of ecomorph, and that anoles in warmer thermal environments will have a higher saturated:unsaturated lipid ratio.

To test this, they are conducting three studies. First, they quantified body temperature of anoles from warmer and cooler areas within the grass-bush, trunk-crown, and trunk-ground ecomorphs in Puerto Rico (Figure 1). Second, to test for lipid composition plasticity, A. carolinensis male and female pairs were housed in either a 26°C or 35°C room (6 pairs in each). After six weeks, the lizards were sacrificed and their brains were collected to quantify the lipid composition ratio using mass spectroscopy at the University of Texas Health Science Center in San Antonio. Finally, to quantify membrane fluidity, they are growing astrocytes from A. carolinensis at 28°C and 35°C and predict that astrocytes from the warmer condition will be less fluid than those from the cooler condition.

This study could provide novel insight into how anole species have adapted to their thermal conditions. We look forward to seeing the rest of the results!

Figure 1. Body (dark columns) and perch (light columns) temperature comparisons between species that perch in the sun (sun) versus in the shade (shade).

Figure 1. Body (dark columns) and perch (light columns) temperature comparisons between species that perch in the sun (sun) versus in the shade (shade).

SICB 2016: Lizards Rapidly Generate More Force During Locomotion than Biting

*The following post was written by Chris Robinson, a Master’s student in Matt Gifford’s lab at the University of Central Arkansas.*

Like at every SICB conference, anoles are well represented among the talks and posters here in Portland and we here at the Anole Annals couldn’t be more thrilled to see the love for one of our favorite genera.

Christopher Anderson, a post-doctoral associate in Thomas Roberts’ lab at Brown University, gave a talk examining how muscle physiology influences whole organism performance in five species of anoles. His group examined two muscles, the M. ambiens pars ventralis (a swing phase muscle of the leg important for locomotion) and the M. abductor mandibulae externus superficialis anterior (a muscle in the jaw used in biting), to see if they differed from each other in how they perform in order to meet their functional demands. The muscle of the leg, which is used in sprinting, is cyclically activated and deactivated as an organism moves, whereas the muscle of the jaw is used more episodically.

Anderson and his colleagues found that the leg muscle builds passive tension at shorter lengths and has a twitch time that is 1.3-2.0 times faster than that of the jaw (to see how twitch time relates to sprint speed, see the post about Noel Parks’ poster). From this, Anderson concluded that these muscles are tuned to meet their physiological demands. Locomotion muscles, which are used frequently, generate a lot of force rapidly and the quickly developing passive tension in these muscles may serve as a form of protection for the muscle during active lengthening.

SICB 2016: Genetic Drift and Morphological Adaptation in Anolis sagrei from the Bahamas

Hanna Wegener giving her talk on Anolis sagrei from the Bahamas at SICB 2016

Hanna Wegener giving her talk on Anolis sagrei from the Bahamas at SICB 2016

Small islands are great systems in which to study evolution, in part because their isolation and simplified landscapes makes them amenable to experimental studies. For example, previous experimental work on Anolis sagrei in the Bahamas by Losos et al. (1997) and Kolbe et al. (2012) found evolutionary changes in hindlimb length driven by adaptation to structural habitat over only a few years.

Hanna Wegener, a Ph.D. student studying with Jason Kolbe at the University of Rhode Island, wanted to know if morphological differences associated with habitat use also manifest in natural (rather than experimentally introduced) populations of Anolis sagrei from the Bahamas. She examined genetic (microsatellite) and morphological variation from male and female A. sagrei on seventeen islands in the Bahamas. Despite the islands being separated by very small geographic distances (no more than three kilometers and typically only a few hundred meters), populations on the islands were genetically differentiated. Her genetic analysis further found high levels of inbreeding on each island.

Unlike the findings on the experimental islands, Hanna did not find any correlation between perch diameter and hindlimb length. She did find that female density was high on the islands, and that density correlated strongly with head length and injury frequency, suggesting that competition influences morphological differentiation on these islands. Overall, Hanna found that morphological patterns varied considerably among islands and among males and females. She suggests that this variation is due to stochastic effects on small islands, namely genetic drift, due to the extinction and colonization dynamics in response to hurricanes.

SICB 2016: Hot Lizards in the City

Andrew Battles presents his work on Anolis cristatellus and A. sagrei at SICB 2016.

Andrew Battles presents his work on Anolis cristatellus and A. sagrei at SICB 2016.

Greetings from SICB! Sessions are off to a roaring start here in Portland. At Monday’s poster session, Andrew Battles presented his work on the thermal ecology of urban anoles. Andrew, a Ph.D. student working with Jason Kolbe at the University of Rhode Island, presented his work in the poster session for the prestigious Huey award.

Around the world, many natural habitats are being replaced with artificial, heat-absorbing structures, such as concrete and metal. This is a really big deal for the animals that perch on these substrates, particularly ectotherms, which derive their heat from external sources. Andrew examined environmental temperatures and canopy openness at a variety of urban and natural sites in (and around) Miami, Florida. What he found was that urban perches (posts, building walls, etc) were considerably warmer and more exposed than natural perches.

He then examined body temperatures for the lizards Anolis cristatellus and A. sagrei that are commonly found in those habitats. On average, A. sagrei had higher body temperatures than A. cristatellus. Both species benefitted from warmer urban structures early in the morning, as they were able to reach temperatures in their preferred range sooner than in the cooler natural sites. In light of these results, Andrew’s next work will examine patterns of physiological divergence in urban and natural habitats. Congratulations to Andrew for being a finalist (and the sole Anolis ambassador) in this year’s Huey Award Symposium.

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

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.

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!

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