Category: New Research Page 22 of 66

*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.

Kathleen Foster, a Ph.D. student in Tim Higham’s biomechanics lab at the University of California, Riverside, gave an interesting talk on how different anole ecomorphs use their limbs. We characterize Anolis species by the portion of the habitat they use (e.g. twig/bush, trunk-ground). Species of the different ecomorphs often show stark differences in external morphology and behavior, which have evolved to match the microhabitat they use. Foster hypothesized that those differences in morphologies may lead to differences in locomotor kinematics.

Foster used high-speed video cameras to record lizards running on surfaces of different diameter and inclination, and digitized forelimb and hind limb joints in all the trials. She compared the limb movements of six Puerto Rican Anolis species, using two species from each of the grass-bush, trunk-ground, and trunk-crown ecomorphs. Using multivariate analyses, she found three major results:  All ecomorphs used a similar strategy of modulating their hind limbs differently than their forelimbs when moving on the different inclines. Interestingly, when comparing ecomorphs, Foster showed that grass-bush species used both their forelimbs and their hindlimbs differently than the other ecomorphs. Furthermore, the two species within the grass-bush ecomorph use their forelimbs differently than each other.

Check out some of Kathleen’s other projects on her website.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

*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.

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.