All posts by mjohnson216

JMIH 2017: Nobody Gets Tired of Looking for Anoles!

Amy Yackely Adams presents at JMIH 2017.

Amy Yackel Adams presents at JMIH 2017.

All anole field biologists have been there, right? It’s the middle of the night, and you’re walking around the forest searching for sleeping lizards in the trees. You’re probably wearing a headlamp, so the bugs are flying around your face, and your eyes start to strain as you get sleepy and you’re entering hour three or four of the search. This searcher fatigue could lead to the kinds of unintentional bias that can interfere with our research. But there’s good news when it comes to anoles, as Amy Yackel Adams, a statistician with the USGS in Fort Collins, Colorado, reported on the last day of JMIH.

Dr. Yackel Adams works with a Rapid Response Team whose goal is to prevent the spread of the worst invasive species. When a report came in of a sighting of a brown tree snake on the island of Saipan (in the Northern Mariana Islands, western Pacific Ocean), the team of experienced herpers deployed to Saipan and began intensive nightly surveys to assess the possibility of a brown tree snake population there.  Luckily, they didn’t find any of these snakes in the surveys, but they did log 20,000+ sightings of other vertebrates! These included emerald tree skinks, several species of geckos, a variety of small mammals, and the green anole (Anolis carolinensis). Dr. Yackel Adams saw an opportunity to use this rich dataset to statistically test for two types of bias that could occur in such surveys – searcher fatigue (both across the 4-hour nightly searches, and across the up-to-31 day deployment), and searcher bias in taxon detection.

The team of 29 searchers covered a total of 387 km of transects during the 31 days, and found a total of 5,800 sleeping green anoles during this time. (Wow!!) In terms of short-term searcher fatigue, there was a slight decrease in tree skink and mammal sightings as the night progresses, and gecko sightings were generally stable over the night, but far MORE green anoles were sighted in the later hours of the night. And over the long term, skinks and anoles were MORE likely to be detected the more nights a searcher worked, and there was no evidence of long-term searcher fatigue.  So, that’s why my take-home message was “nobody gets tired of looking for anoles!”

There was, however, significant taxonomic bias among the searchers – for example, the skink-to-anole sighting ratios ranged from 0.86 to 9.5. Dr. Yackel Adams concluded that this type of bias could be a real problem for certain kinds of studies, and we should be aware that differences among sightings by our survey team members could be potentially problematic in statistical analyses.

JMIH 2017: Brown Anoles Thrive under Artificial Night Light

Chris Thawley presents at JMIH 2017.

Chris Thawley presents at JMIH 2017.

For most of the history of life on earth, the only sources of light at night were the moon and stars. Yet with the invention and rapid spread of electric light, species around the world now face a novel evolutionary pressure: artificial light at night, or ALAN. Artificial light likely has an especially strong effect on animals in city habitats, such as the urban-adapted brown anole lizard, Anolis sagrei. Chris Thawley and Jason Kolbe at the University of Rhode Island set out to determine whether brown anoles were negatively impacted by ALAN.

In addition to their abundance in urban environments, brown anoles are a particularly good species for this study.  Previous studies of brown anoles have shown that photoperiod influences the onset of reproduction at the beginning of the breeding season, and that several behavioral traits change under artificial light. In addition, work by Moore and Menaker has shown that pineal production of melatonin in this species is significantly altered by photoperiod.  So, would ALAN influence brown anole growth and reproduction?

Chris and Jason collected lizards from south Florida and set up a lab experiment where some lizards experienced a normal photoperiod, and others were exposed to ALAN that mimicked landscape lighting. Their results were quite unexpected! ALAN actually increased female growth, resulted in eggs laid earlier in the season, and increased the reproductive output of small females – but did not affect the number or mass of eggs or hatchlings.  And, ALAN females did not exhibit more stress (measured via circulating corticosterone) than control females.

So are brown anoles just superlizards? Do they have no trade-offs that result from ALAN? Chris suggested that it’s possible that such trade-offs may appear in studies over a longer time period, or in traits not measured here. Or, perhaps ad libitum food and the absence of predators in the lab remove the costs of ALAN. Or, maybe these really are indefatigable lizards!

JMIH 2017: Costa Rican Anole Ecology

JMIH

Greetings from Austin, Texas, and the Joint Meeting of Ichthylogists and Herpetologists! Chris Thawley and I have appointed ourselves to be your AA reporting team from JMIH, and we’re aiming to post updates from each of the 8 anole talks and posters at this meeting.

Brian Holt

Brian Folt

On the first day of the conference, there were two exciting talks on the ecology of Costa Rican anoles. The first was by Brian Folt, a graduate student in Craig Guyer’s lab at Auburn, who developed a model of predator-prey co-occurrence where one of the prey were anoles (Anolis (Norops) humilis) and the predators were…spiders?!  Yes, wandering spiders, or ctenids, can prey upon the small anoles on the forest floor. (The other putative prey were poison dart frogs, who have a relatively similar life history to anoles.) Brian performed an extensive field study in 14 plots at La Selva Biological Station, conducting visual encounter surveys for anoles, frogs, and spiders, and recording arthropods in leaf litter samples. He used two-species occupancy models to determine how prey were affected by the presence of the predator and by resource abundance in the leaf litter. The result? Anole occupancy was lower where spiders were absent, and the detection probability of anoles was higher when spiders were present and detected. This suggests that anoles are responding behaviorally, such that they may increase their vigilance when predators are around.

Michelle Thompson

Michelle Thompson

I then ran across the conference center to catch the next anole talk – a terrific presentation by Michelle Thompson, a graduate student in Maureen Donnelly’s lab at Florida International University. Michelle studied whether thermal quality differed across the stages of forest succession, and how that affected Anolis (Norops) humilis and A. (N.) limifrons distributions. She worked across transects of pasture, secondary forest, and old growth forest in both upland and riparian sites. Michelle measured the thermal quality of each habitat, the thermal preferences of the lizards, and the location and abundance of the lizards. She found that thermal quality was lowest in the pasture sites, as temperatures were frequently higher than the lizards prefer. Yet, in these pasture sites, riparian habitat with remnant trees provided a thermal refuge for the lizards. This kind of work can help us understand why and how species may respond differently to human-caused alterations in habitat structure and temperature in our changing world.

Stay tuned for updates from JMIH, and follow the #JMIH17 hashtag on twitter for more herp-related news!

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Where Are All the Green Anoles?

For the past eight years, my lab has conducted intensive research on green anoles (Anolis carolinensis) in Palmetto State Park in Luling, Texas, about an hour east of San Antonio. This park is beautiful – it’s centered around a swampy area dominated by dwarf palmettos (Sabal minor), and the San Marcos River flows through it. We’ve marked lizards and mapped their home ranges, watched their behavior, measured their morphology and parasite loads, and so much more. In past years, we’ve calculated that the density of green anoles in the park is approximately 0.04 lizards/m2, or about four adult lizards in every 10m x 10m area. We could regularly get sample sizes of around 150 lizards for behavioral studies in the park, but we very rarely collected animals from the park – we left them where we found them!

But this year is different. On three field trips to the park this summer, we have found very few green anoles. On our first visit this year in May, we spent 16 person-hours searching for lizards and found four green anoles. On our second visit in early June, we spent 14 person-hours searching and found eight. Last week, we spent another 12 person-hours and found only two. We see green anoles all over the city of San Antonio, and the students in my team are all skilled lizard spotters and catchers, so this isn’t due to inexperience. Also, we see other species of lizards all over the park – most commonly, Texas spiny lizards, little brown skinks, and house geckos– as well as garter snakes, copperheads, and cottonmouths. We also see tons of frogs.

Garter snake eating a tree frog, at Palmetto State Park. Other herps are thriving there!

Garter snake eating a tree frog, at Palmetto State Park. Other herps are thriving there!

So what happened to the anoles? We’ve considered a number of possibilities. The first thing we thought of was the possibility of feral cats – but we haven’t seen any cats in the park, and we think cats should have the same effect on the other herp species. What if the insect population had crashed? But again, that would affect the other lizards, snakes, and frogs too. This isn’t a year of particular drought or excess rain (and in previous wet and dry years, we’ve still seen lots of anoles), and the vegetation throughout the park largely looks the same as it has in the past. Perhaps an anole-specific disease has spread through this population?

In any case, the paucity of anoles in the park this year suggests that there won’t be many next year either, as there’s almost no one around laying eggs. It’s a bummer, because we’ve had such success here in the past.

Any ideas to explain this, AA readers?

 

Work we’ve published from our previous research in Palmetto State Park:

  • Dill, A.K., T.J. Sanger, A.C. Battles and M.A. Johnson. 2013. Sexual dimorphisms in habitat-specific morphology and behavior in the green anole lizard. Journal of Zoology 290: 135-142.
  • Battles, A.C., T.K. Whittle, C.M. Stehle, and M.A. Johnson. 2013. Effects of human land use on prey availability and body condition in the green anole lizard, Anolis carolinensis. Herpetological Conservation and Biology 8: 16-26.
  • Bush, J.M., M.M. Quinn, E.C. Balreira, and M.A. Johnson. 2016. How do lizards determine dominance? Applying ranking algorithms to animal social behavior. Animal Behaviour 118: 65-74.
  • Stehle, C.M., A.C. Battles, M.N. Sparks, and M.A. Johnson. In revision. Prey availability affects territory size, but not territorial display behavior, in green anole lizards. Acta Oecologica.

Metabolism Rate Data on Anoles?

I’m hoping that some of you out there have been collecting Basal Metabolic Rate or Resting Metabolic Rate data on Caribbean anoles!

I’m working with a group of scientists on a large-scale comparative database on circulating hormones in free-living vertebrates – we call our collaboration HormoneBase – and we’re hoping to look at relationships between hormone levels and metabolism. (We’ll be presenting some of this work at the Society of Integrative and Comparative Biology meeting in January 2018 – check out our symposium announcement here!) We have a good list of anole species in the database, thanks to the work of Jerry Husak and Matt Lovern (2014), but it seems that very little metabolism rate data are available for these species. Do you know of such data, or do you have them – published or unpublished? If so, please contact me (mjohnso9@trinity.edu)!

 

Reference:

Husak JF and MB Lovern. 2014. Variation in steroid hormone levels among Caribbean Anolis lizards: endocrine system convergence? Hormones and Behavior 65:408-415.

SICB 2017: Are Anoles Less Stable When Running Without Using Claws?

Photo courtesy of Catalina Mantilla

Photo courtesy of Catalina Mantilla

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

Catalina Mantilla, a Ph.D. candidate at Florida International University working with Tonia Hsieh of Temple University, is interested in how anoles use their toepads and claws when they run. For most animals, movement on vertical perches such as tree trunks or buildings usually requires specialized morphologies to adhere to these substrates. While many species have evolved adaptations for moving through complex arboreal habits (e.g., prehensile tails or feet, sticky pads, spines), anoles evolved enlarged toepads and distinct claws, presumably to allow for better adhesion. The morphologies of these specialized structures can greatly impact performance; for example, greater toepad area is associated with greater clinging ability. Catalina wanted to better understand how toepads and claws work together to enhance running performance.

Catalina collected 17 males from four Anolis species (A. carolinensis, A. sagrei, A. cristatellus, and A. distichus). Each male was tested in four different running courses to test performance at difference inclines and on different substrates. Two of the courses were positioned at a 45° incline and two at a flat (0°) incline. Plexiglass covered one course at each incline to allow the use of toepads and eliminate the use of claws. Nylon mesh covered the other course at each incline to test the use of both toepads and claws. Performance was evaluated using mean relative sprint speed, relative stride length, and stride frequency.

Catalina found, unexpectedly, that when the lizards ran on the level plexiglass, they ran slower, took shorter strides, and increased their stride frequency compared to when they ran on the inclines. These results suggest that anoles are less stable when they can’t use their claws! in addition, these data support the idea that the combination of toepads and claws is important for their running performance. In the future, Catalina hopes to increase the number of species in this study to determine the effect of ecomorph on claw and toepad interactions during running, and to evaluate limb function changes when running across different inclines.

SICB 2017: How Anoles Climb Trees: Ecomorph Differences in Neuromuscular Function

Kathleen Foster presents her work to a packed room at SICB.

Kathleen Foster presents her work to a packed room at SICB.

Regular readers of AA will be familiar with the differences in microhabitat use that define the Anolis ecomorphs, but do species with such distinct structural habitats move differently on their specialized perches? In other words, does muscle function differ between the ecomorphs? In the very last session at this year’s SICB, Kathleen Foster, currently a postdoctoral researcher at the University of Ottawa studying the biomechanics of fish locomotion (come back to anoles, Kathleen!), presented a portion of her graduate work in Tim Higham’s lab at the University of California, Riverside, to address this question. She used high speed video to film five species of anoles running on broad and narrow perches at two angled inclines, combined with electromyography to record fore- and hindlimb muscle activity during running.

Photo courtesy of Kathleen Foster.

Photo courtesy of Kathleen Foster.

Kathleen found that all five species had greater motor unit recruitment on steeper inclines than on horizontal perches, and that muscle activity is shorter but begins more abruptly on inclines. Further, recruitment of the gastrocnemius (a “calf” muscle) was greater on broad perches, because the way lizards sit on narrow perches limits the function of this muscle. If you’ve seen how anoles position their feet on both sides of narrow perches, it’s easy to understand how this posture prevents effective propulsion by ankle extension. Kathleen also found several intriguing differences that distinguish trunk-ground species’ muscle function from trunk-crown and crown-giant species. The activity of the caudofemoralis (a limb retractor muscle in the hindlimb) changes more in trunk-ground species as a function of incline, and trunk-ground species use the biceps and gastrocnemius more in the early stance phase of propulsion than trunk-crown species.

Overall, these data help us understand how specialization in neuromuscular function can allow different anole species to successfully move through their varying habitats, and offer insight into how behavioral differences depend on the muscles that underlie them.

SICB 2017: Thermal Ecology and Invasion Biology: Anolis cristatellus Invades Dominica

Jeanel Georges with her poster at SICB.

Jeanel Georges with her poster at SICB.

The beautiful island of Dominica used to be home to only one anole (Anolis oculatus), but about 20 years ago, the Puerto Rican crested anole (Anolis cristatellus) showed up. Jeanel Georges, a graduate student in Matt Watson’s lab at Midwestern State University in Wichita Falls, Texas who is originally from Dominica, noticed that while A. oculatus occurs in all the ecological zones of the island, A. cristatellus is absent from the cooler, wetter uplands. With an international group of collaborators, Jeanel examined the thermal habitat use, sprint speed, and bite force of both species to determine what may limit the spread of A. cristatellus across the island.

At a lowland site where the two species co-occur, both species had higher body temperatures that the operative temperatures randomly available in the environment. In the much cooler upland site, A. oculatus had much higher body temperatures than the operative models, but these body temperatures were cooler than that species experiences in the lowland site. Jeanel also found that the two species had stronger bite forces and higher sprint speeds in the lowland site than A. oculatus had in the upland site. These data suggest that A. cristatellus and A. oculatus are partitioning the thermal environment of Dominica, and as climate change alters the temperatures available to lizards on the island, the interactions between these two species may change.

SICB 2017: It’s Getting Hot in Here: How Brown Anoles Respond to Extreme Heat in Greenhouses

Austin Hulbert with his poster at SICB 2017.

Austin Hulbert with his poster at SICB 2017.

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

Austin Hulbert, an undergraduate in Dan Warner’s lab at Auburn University, presented a poster on the behavior of brown anoles (Anolis sagrei) in a novel environment: a few very hot greenhouses in Auburn, Alabama. Brown anoles are an invasive species, most notably in Florida, but some populations have been found farther north in states including Louisiana, Alabama, Mississippi, and Georgia. As ectotherms migrate to higher latitudes, they often have to deal with different thermal environments and must alter their behaviors accordingly. Austin was interested in determining the activity patterns of a population of brown anoles inhabiting a group of greenhouses in Alabama.

During the summer he found that temperatures inside the greenhouses were consistently higher than those outside. Temperatures drastically increased each morning, up to peak temperatures between 11am and 3pm (on average, 45°C inside the greenhouse and 37°C outside). In the evenings, the temperatures again cooled. Austin surveyed the greenhouses and the surrounding areas for anoles during the morning, peak, and evening hours and determined the type of substrate each individual was using (i.e. brick or concrete, ground, metal, or wood). On average, brown anoles were more abundant inside the greenhouses than outside during the morning and peak times. He also found that more of the brown anoles perched on wooden substrate in the morning and evening. During peak hours more lizards perched on the ground. Because temperatures are often cooler closer to the ground, the lizards may be altering their behavior to deal with the extreme heat in the greenhouses during the hottest part of the day. While the visual survey focused on lizards perched in the open areas visible to the surveyor, there may have been individuals hiding under undisturbed objects as a means to keep cool during peak hours. In the future, Austin would like to compare the thermal tolerance of this group of brown anoles to those of populations in Florida to determine if inhabiting these greenhouses has resulted in adaptions to tolerate their more extreme temperatures.

SICB 2017: Is Maternal Stress Transferred to Offspring?

Jerry Husak presenting at SICB 2017.

Jerry Husak presenting at SICB 2017.

This post was co-written by Maria Jaramillo, an undergraduate in Michele Johnson’s lab at Trinity University.

A mother’s experience during gravidity may alter her offspring’s development, particularly through altering hormone levels in the yolk of her eggs. Stress hormones such as corticosterone (CORT) alter various aspects of offspring phenotype following in ovo exposure, and physical exercise elevates CORT in many vertebrates. In the work he presented at SICB, Jerry Husak and colleagues used exercise and food restriction to manipulate female Anolis carolinensis CORT, and to then determine whether the increased CORT was transferred to the females’ egg yolks.

Jerry assigned females to one of four treatments with different combinations of exercise and food restriction: 1) no exercise, regular diet; 2) no exercise, restricted diet; 3) exercise, regular diet; and 4) exercise, restricted diet.  He found that maternal exercise increased maternal CORT (as expected), but surprisingly did not result in higher CORT in the eggs. Further, diet restriction did not affect maternal CORT, but moms with restricted diets laid eggs with reduced CORT.

This study suggests that anole mothers may manipulate the environments of their eggs in ways we don’t yet understand – the mechanisms by which CORT is transferred to eggs is an area ripe for future study!

SICB 2017: Social Hierarchy Influences Green Anole Behavior

Sukalia Miller with her poster at SICB.

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.

SICB 2017: Green Anoles, Brown Bodies: Are Brown Lizards “Losers”?

brittneyAnimals frequently compete over resources, and the outcomes of these aggressive interactions depend on a number of factors – one of which is the animals’ previous social experiences. If an animal wins a fight, it may be more likely to win subsequent fights (a “winner effect”), and if it loses, it may be more likely to lose subsequent fights (a “loser effect”).  Garcia et al. (2014, Animal Behavior) previously showed that green anoles exhibit loser effects, but not winner effects. Brittney Ivanov, research technician in Michele Johnson’s lab at Trinity University, wondered whether, since body color in green anoles is associated with social dominance, were color changes in green anoles associated with these loser effects? Could she cause a green anole to be brown if it was forced to lose social contests?

Brittney conducted an experiment using 16 male green anoles. First, in three consecutive days, these focal males interacted with a larger “trainer” male in the trainer male’s home cage for one hour. On the fourth day, the focal males interacted with a size-matched novel male in a cage that was new to both lizards. If the focal males were effectively trained to lose in the first three trials, she predicted that they would lose this fourth trial.

In the series of size-matched trials, 7 of the 16 contests resulted in a clear winner and loser, and 6 of those 7 focal males lost that trial. Further, focal males were less aggressive in the size-matched trial than they were in their previous training trials. These data support the presence of a loser effect in green anoles. Consistent with her previous work, Brittney also found that lizards that were more often green prior to the trials were more likely to win their trials, showing that body color is important in social contests.

brittneycolorgraph2This experiment revealed new findings about loser effects and body color. Focal males who lost their size-matched trial were more likely to be brown in the days after the trials – and not only that, they were more likely to become brown after the trials (so, these weren’t just loser males who had been brown all along).

All together, Brittney’s results show that body color can provide important information about a green anole’s fighting ability or motivation, or its recent social experience, and that dynamic body color influences multiple stages of social interaction in this species.

Anolis sagrei embryo with axis duplication. Photo from Sanger Lab.

SICB 2017: How To Make A Lizard With Two Heads, Or Thermal Stress On Eggs Produces Embryonic Abnormalities

Judy Kyrkos presenting her poster at SICB

Judy Kyrkos presenting her poster at SICB

Anole biologists are focusing more and more on thermal ecology and the adaptations associated with heat stress in adult lizards, but what happens when an egg experiences heat stress? Judy Kyrkos, a senior undergraduate in Thom Sanger’s lab at Loyola University, Chicago, presented a fantastic study addressing this question in Thursday’s poster session.

Judy and Thom conducted two experiments to determine the effects of thermal stress on embryonic development in Anolis sagrei. In the first, they incubated 533 eggs at one of five temperatures (ranging from 27-39°C) for 12 days. As predicted, they found that eggs at higher temperatures – and particularly those over 33°C – experienced lower survival and a higher rate of developmental abnormalities, most of which occurred in facial and brain development.  In the second experiment, they heat-shocked 60 eggs at 39°C for one hour on the day they were laid, and then incubated them at 27°C until hatching. 50 of those 60 eggs exhibited abnormal morphologies. Further, overall growth of embryos in heat-stressed eggs was also reduced. Comparing embryos at developmental stage 9-10, lizards incubated at 36°C had smaller SVLs than those heat-shocked in the second experiment, which were in turn smaller than the lizards incubated at 27°C. Altogether, these are a lot of challenges for a vulnerable embryo, and Judy’s results suggest that the rising temperatures anticipated as a function of climate change may affect anoles more dramatically than we’ve yet recognized.

 

 

SICB 2017: Masking the Parietal Eye in Green Anoles

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

Samantha Adams presenting her poster at SICB.

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.

Evolution 2016: Ecomorphology in Caribbean Eleutherodactylus Frogs

Common_CoquíStephen Jay Gould famously claimed that evolution is “utterly unpredictable and quite unrepeatable,” and we Anolis biologists have relished in proving that statement wrong. In his talk in Austin this week, Alejandro Gonzalez Voyer of UNAM (with coauthors Alvaro Dugo Cota and Carles Vilá) showed that anoles aren’t the only Caribbean herps to exhibit the independent, repeated evolution of ecomorphs across islands – Eleuthrodactylus frogs have joined the club!

Among the remarkably diverse Caribbean Eleuthrodactylus species, nine ecotypes exist, including terrestrial, leaf-litter, aquatic, riparian, bromelicolous, arboreal, fossorial, cavernicolous, and petricolous specialists. Gonzalez and his coauthors first determined that these ecotypes evolved repeatedly, and showed that their distribution resulted from both invasion across islands and intra-island speciation. They also found that eight of the nine ecotypes cluster in morphological space and exhibit significant convergence. (The ninth, the fossorial ecotype, is composed of a monophyletic clade from Hispaniola and so convergence could not be tested.)

In sum, it appears that Eleutrodactylus ecotypes are indeed ecomorphs, and that evolution may be utterly predictable and quite repeatable after all.

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

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

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

Zac at SICB in Portland

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

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 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: 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!