SICB 2016: Stress on the Job – A Case Study of Anolis carolinenesis

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Variables to measure stress in Anolis carolinensis

Does enrichment increase the well-being of Anolis carolinensis in captivity? Scientists become more and more aware of animal welfare, aiming to reduce stress levels of animals in captivity. Glenn Borgmans from the University of Antwerp (Belgium) was interested in the effect of environmental enrichment on stress levels of Anolis carolinensis. Glenn measured multiple variables to assess stress levels during an acclimation period (‘acclimation’) and subsequently  under two experimental conditions: no enrichment (‘deprived’) and high amounts of enrichment (‘enrichment’). To asses stress levels, he measured body mass, tailbase width, heterophil/lymphocyte ratio (a measure of stress) in the blood, change in body coloration (brightness), fecal corticosterone levels and overall behavior.

 

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Increased heterophil/lymphocyte ratio suggests that lizards are more stressed during acclimation period as compared to cages with no enrichment (deprived) or higher amounts of enrichment.

Animals during the ‘acclimation’ period showed significantly higher levels of stress than animals housed under ‘deprived’ or ‘enriched’ conditions. This is surprising, because acclimation cages provided a baseline level of enrichment that is most commonly used in research and pet trade. Interestingly, males and females showed differences in behavior when stressed. Males showed overall higher activity (walking and climbing) and females showed reduced levels of activity. No difference between males and females was found in other variables. On the other hand, as for humans who are encountering stress on a daily basis, they can release some of that stress through playing games such as 아인카지노.

Glenn suggests that elevated stress levels during the acclimation period was due to stress experienced prior to the experiment. Individuals were obtained from pet trade and showed high levels of stress for most variables. In pet trade multiple anoles are housed together, which might increase stress levels and thus explain his findings. To test this hypothesis Glen would like to look at how density affects stress levels of lizards in captivity.

SICB 2016: Modeling Color Vision in Anoles

Leo Fleishman of Union College

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?

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 Among Performance, Growth, and Immune Function in Juvenile Lizards

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Dr. Jerry Husak presents his poster at SICB 2016

*This post was written by David Delaney, a Ph.D. student in Fred Janzen’s lab at Iowa State University.*

Organisms must balance tradeoffs between performance, growth, immune function, and reproduction in order to maximize fitness. Adults and juveniles experience different life history pressures because juveniles are not reproductively mature, whereas adults should invest in reproduction. Thus, adults and juveniles may balance these life-history traits differently.

Dr. Jerry Husak of the University of St. Thomas presented on a study that he and undergraduate co-author Jordan Roy conducted to examine if adult and juvenile green anoles vary in resource allocation. To do this, 22 lizards were trained on a treadmill whereas 23 lizards were not. Training consisted of running lizards on a small pet treadmill 2 times per week. The incline was increased every two weeks for a period of 9 weeks to increase training intensity.

They found that training reduced the body mass of juveniles, which did not occur for adults. Training increased endurance capacity which also occurred in adults, however adults had a sex effect that juveniles did not. Training did not affect body length in juveniles, whereas it increased adult body length. Training eliminated the sex differences in juvenile immune function which did not occur for adults. Training increased hematocrit and heart ventricle mass which was also found for adults. In addition, juveniles exhibited very high variation in their response to training. Overall this study shows that juvenile green anoles balance these tradeoffs differently than adults, which likely reflects differences in the importance of certain life history traits throughout ontogeny.

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

John David Curlis presenting his poster in Portland.

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: The Consequences of Losing in Females

You lookin’ at me? Photo credit to Tim Norriss

It’s often said that winning isn’t everything. This may be true for humans and the games we play, but, unfortunately, for most animals losing a contest can have serious implications for whether they survive or reproduce. The study of animal contests has been thoroughly studied in males, and we know that losing to a rival can mean you get less or no mating success. However, we know far less about the consequences of winning and losing if you are a female. Jess Magaña and Matt Lovern (from Oklahoma State University) asked what happens to females after they win or lose a contest, and they had one of my favorite talk titles ever: “Small and large lizards agree in defeat but react differently to victory.”

They studied brown anole females, which are known to show aggression toward each other. Winners and losers were pre-determined by residency in a cage. Females who got to compete in their home cage were winners, and those who were placed into another lizard’s cage were the losers. They were allowed to interact, and then Magaña monitored their reproduction thereafter. Previous work had shown that losers laid eggs that hatched more quickly, suggesting that offspring were given less yolk and would perhaps be less successful because of it.

Comparisons between winners and losers reveleaed surprisingly little difference in most reproductive traits, such as egg size, time to hatch, and sex ratio. However, when they looked at the effects of body size on reproductive traits, there was a marked difference between winners and losers. In losers, investment in reproduction was unrelated to body size. In winners, though, size was related, and size reflects age in this species. Small (young) winners laid eggs that hatched quickly, but large (old) winners laid eggs that took longer to hatch. They interpreted this as different strategies of investing in potential future reproduction: old winners should invest in current offspring, whereas a young winners should invest in potential future offspring. This interesting finding highlights the fact that there is still much to be learned about the subtlety of how a mother’s environment and experiences can shape her offsprings’ life.

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.

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