Category Archives: New Research

The Not-So-Bitter Future of Coffee: Anolis Lizards as Biocontrol Agents in Mainland and Island Agroecosystems

Figure 7. Anolis gundlachi, Orocovis, Puerto Rico.

Figure 1. Anolis gundlachi, Orocovis, Puerto Rico.

The agroecosystems that produce the life-sustaining stimulant we know as “coffee” have long been used as model systems to study complex ecological interactions and ecosystem services, with numerous studies revealing trophic interactions among coffee plants, pests, and pest-predators. Despite the high abundance and overlapping distribution of Anolis lizards, relatively few studies have addressed their functional role in agriculture. In our recent study titled, “Anolis Lizards as Biocontrol Agents in Mainland and Island Agroecosystems,” my colleagues and I explore the biocontrol potential of anoles against the world’s most devastating coffee pest, the coffee berry borer (Coleoptera: Hypothenemus hampei) in mainland and island settings.

My vision of agricultural landscapes as post-apocalyptic biodiversity deserts was trumped the minute I stepped foot onto a shade coffee farm in Orocovis, Puerto Rico. Far from the dystopian nightmare that I had envisioned, this diversified shade coffee farm bustled with the herpetological glory and natural complexity of a native forest (Fig. 1). Furthermore – and perhaps most importantly – the farmer complained not of issues with crop yield, pests, and disease.

As a plant, coffee occurs naturally in the forest understory and is cultivated traditionally among native shade trees as an understory crop. While pressures to increase production have led many farmers to transition to more intensive practices (i.e., the reduction of shade cover and application of agrochemicals to manage crop pests), these methods are becoming increasingly unsustainable and insufficient in light of emerging biological threats. In addition to climate change and the emerging coffee rust disease, the coffee berry borer poses a unique threat for dozens of coffee growing nations and nearly 20 million small-scale farmers who depend on coffee production as a primary commodity and means of subsistence. While the coffee berry borer (CBB) is capable of inducing 60-90% reductions in yields and persists unaffected by topical pesticides, our understanding of the predator-prey interactions that drive its top-down control and how these factors vary across management regimes and eco-geographic space has profound socio-economic and environmental implications for biological control.

Representative photographs of diversified shade coffee in Mexico (a), diversified shade coffee in Puerto Rico (b), intensive sun coffee in Mexico (c), and intensive sun coffee in Puerto Rico (d).

Figure 2. Representative photographs of diversified shade coffee in Mexico (a), diversified shade coffee in Puerto Rico (b), intensive sun coffee in Mexico (c), and intensive sun coffee in Puerto Rico (d).

To assess the biocontrol capacity of anoles, we conducted experimental and field-based tests of how CBB populations respond to anole predation across mainland (Mexico) and island (Puerto Rico) coffee farms with parallel forms of land-use intensity. Anole functional response and infestation reduction potential were assessed by simulating pest outbreaks in the lab, while coffee farms were surveyed along complementary gradients of intensification. Organic, diversified shade coffee farms were representative of low-intensity production, and sun coffee monocultures that included the application of agrochemicals were representative of high intensification (Fig. 2). Continue reading The Not-So-Bitter Future of Coffee: Anolis Lizards as Biocontrol Agents in Mainland and Island Agroecosystems

Evidence for evolutionary determinism in the signal design of lizards?

Photographs of a subset of lacertid lizard species used in this study. From the left top to the right bottom: Acanthodactylus beershebensis, Lacerta bilineata, Dalmatolacerta oxycephala, Podarcis melisellensis, Tropidosaura gularis, Podarcis siculus, Heliobolus lugubris, Algyroides nigropunctatus, Lacerta media.

Photographs of a subset of lacertid lizard species used in this study. From the left top to the right bottom: Acanthodactylus beershebensis, Lacerta bilineata, Dalmatolacerta oxycephala, Podarcis melisellensis, Tropidosaura gularis, Podarcis siculus, Heliobolus lugubris, Algyroides nigropunctatus, Lacerta media.

The vast array of signals used in animal communication is a continuous source of awe and a hot topic in evolutionary and behavioral research. One important factor contributing to the signal diversity we witness today is ‘signal efficacy’: the ability of a signal to travel efficiently through the environment and attract the receiver’s attention. With this in mind, natural selection is expected to mold signal design for maximum efficacy of information transmission and detectability, leading to signal variation among populations/species living in different environments. To illustrate, a recent study by Tess Driessens and colleagues assessed the degree of variation in the dewlap design of Anolis sagrei by comparing 17 populations distributed across the Caribbean (Fig. 1).

Phylogenetic relationships among seventeen Anolis sagrei populations. Pie charts illustrate dewlap pattern proportions for each population per sex (black = solid; light grey = marginal; dark grey = spotted). Photographs represent male and female dewlaps of typical individuals from every population.

Fig. 1 — Phylogenetic relationships among 17 Anolis sagrei populations. Pie charts illustrate dewlap pattern proportions for each population per sex (black = solid; light grey = marginal; dark grey = spotted). Photographs represent male and female dewlaps of typical individuals from every population.

Their findings showed large interpopulational variation in dewlap size, pattern, and color, and more interesting, they established a link between the dewlap design of brown anoles and the environment they live in. Lizards occurring in more ‘xeric’ environments had a higher proportion of solid dewlaps with a higher UV reflectance; lizards inhabiting ‘mesic’ environments had predominantly marginal dewlaps showing high reflectance in red. This was true for both males and females. Like Ng et al. (2011) and their observations on dewlap variation in A. distichus across an environmental gradient, Driessens et al. (2017) interpret their findings as evidence for adaptive divergence of a signaling apparatus.

Surprisingly though, while there are numerous great examples of comparative studies finding support for convergent evolution in visual and acoustic signaling systems, (e.g. Endler 1992; Fleishman 1992; Nicholls & Goldizen 2006, to say a few), similar (comparative) studies, but then, on the phenotype of chemical signals are almost entirely lacking. This is probably due to the combination of only very recent developments in chemical analytical and statistical comparative tools, the time researchers need to assemble a large-scale multi-species chemical dataset, and perhaps due to our own predisposition to visual and auditory signals. Currently, the proper analytical tools for studying natural products chemistry are available and affordable, permitting comprehensive taxon-wide research on the evolution of chemical signal diversity and design. Ultimately, there has never been a better time as now to be a comparative chemical ecologist.

Photograph of the cloacal region of a male lacertid lizard (Lacerta agilis), showing his numerous femoral pores with protruding glandular secretion.

Photograph of the cloacal region of a male lacertid lizard (Lacerta agilis), showing his numerous femoral pores with protruding glandular secretion.

Finally, three Belgians, two Spaniards and one Greek (sounds like the start of a joke with ample potential) took up the challenge to examine variation in the chemical signal design of lizards. Although underrepresented in studies on chemical signal diversity, lizards are an excellent group for investigating chemical signal evolution, as many of them they bear numerous glands on their thighs that secrete waxy substances, which they deposit while moving through their habitat. These secretions are often considered the leading source of chemical signals involved in lizard communication.

The study started with a quest. A quest to collect gland secretions of as many species as possible (within a PhD timeframe). Luckily, we were fortunate enough to be able to count on the help of many collaborators (Shai Meiri, Chris Broeckhoven, …). We focussed on lacertid lizards, as they are a species-rich family distributed over a wide geographical area, and known to rely strongly on chemical communication in several contexts.

In total, we sampled secretions from 64 species throughout, Europe, Africa, and Asia, covering a wide array of habitats and climate regions: from the Mediterranean maquis over the alpine meadows in the Pyrenees Mountains, to the sandy Israeli dunes and the Kalahari Desert of South Africa (Fig. 2). Back in the lab, we determined the chemical composition and chemical ‘richness’ (number of different chemical compounds) of the secretions using GC-MS, and obtained climate data for all catch-localities from online databases.

Map showing the sample localities of the 64 lizard species under study.

Fig. 2 — Map showing the sample localities of the 64 lizard species under study.

Our gathered data showed considerable variation in the chemical richness and composition of lacertid secretion. Shared-ancestry failed to explain among-species patterns of variation, hinting that chemical signals may change relative rapidly. Most interestingly, our findings revealed a strong relationship between the environmental conditions species live in and the chemical composition of their glandular secretions. On the one hand, lizards living in ‘xeric’ environments, characterized by high temperatures and arid conditions, contained higher proportions of stable and heavy-weight compounds in their secretions. Hot and dry conditions increase the evaporation rate of chemicals, and so, decreasing the longevity of a signal. Stable and heavy-weight compounds most likely reduce evaporation rate and counteract the rapid signal fade-out through evaporation, generating a highly persistent scent-mark. On the other hand, species inhabiting wet, humid conditions produced highly aromatic and low-weight secretions containing numerous different compounds. This chemical mix probably creates a volatile-rich signal that can be used for long-distance airborne communication.

While we cannot deny that these findings of convergent evolution in the design of chemicals signals are fascinating, some would say this outcome is not unexpected.

“[…] a cadre of scientists has taken the […] view, that convergence is the expectation, that it is pervasive, and that we should not be surprised to discover that multiple species […] have evolved the same features to adapt to similar environmental circumstances. From this perceived ubiquity, the scientists draw a broader conclusion: evolution is deterministic, driven by natural selection to repeatedly evolve the same adaptive solutions to problems posed buy the environment. — J. Losos (Improbable Destinies, p. 33)

Nonetheless, I am confident to state that using by far the largest comparative dataset amassed to-date to examine patterns of chemical signal divergence, we have provided strong evidence for a significant relationship between chemical signal design and prevailing environmental conditions, which may results from differential selection on signaling efficacy (Baeckens et al. 2017).

Condition Dependence of Shared Traits Differs between Sympatric Anolis Lizards

A male slender anole (Anolis limifrons)

A male slender anole (Anolis limifrons)

A walk through a tropical rainforest can reveal astonishing forms and colors of organisms – from vibrant poison frogs and coral snakes to the vegetative camouflage of stick insects and other cryptic creatures. Perhaps some of the most dramatic displays of variation can occur between the sexes, where males and females can differ so greatly in appearance that they resemble different species. Research in many systems has demonstrated that much of this variation is driven by sexual selection, the force responsible for the evolution of traits that are important for acquiring mates. Individuals may invest as much energy as possible into such sexually selected traits because doing so will give them a competitive advantage for mate acquisition. These traits are therefore considered condition dependent, as their expression is dependent upon the energetic condition of the individual that possesses them. While condition dependence has been the subject of many studies, it is not well known how it may vary between closely related species that share the same traits. If closely related species vary in condition dependence of their shared traits, then this implies that condition dependence could be important for the evolutionary diversity of sexually selected traits.

The rainforest at the La Selva Biological Station in Costa Rica

The lowland rainforest at the La Selva Biological Station in Costa Rica

Together with students from Grinnell College and Reed College, and as part of an OTS (Organization for Tropical Studies) course that I took as an undergraduate at the University of Virginia, we took to the lowland jungles of Costa Rica to answer this question. We studied two anole species from Costa Rica, the slender anole (Anolis limifrons) and the ground anole (Anolis humilis). Specifically, we tested whether several traits that they had in common exhibited condition dependence, including dewlap size, aspects of jaw morphology, and sprinting speed. To test for condition dependence, we first calculated two conventional indices of body condition, the residual index and the scaled mass index, which both take into account an organism’s mass, given its length. We then obtained residuals from the relationship between our variables of interest (dewlap size, jaw width, jaw length, and sprint speed) and snout-vent length (a measure of body length), which allowed us to control for the fact that trait sizes often scale with the overall size of an animal. Finally, we used bivariate linear regressions to test the effect of our indices of body condition on our residual traits of interest, with a significant positive relationship suggesting condition dependence. We found that dewlap size (a trait important for sexual signaling) and jaw width (a trait important for bite force and male combat) exhibited condition dependence in ground anoles, but not in slender anoles. In contrast, neither sprint speed nor jaw length were condition-dependent in either species. Importantly, the presence of condition dependence in one species, but not the other, implies that the condition dependence of shared traits is evolutionarily labile. Additionally, by detecting condition dependence in the dewlap of ground anoles, which have a larger dewlap given their body length when compared to slender anoles, our findings may indicate that the strength of sexual selection differs between these two species. Lastly, our research suggests that variation in condition dependence of the dewlap among species could contribute to the extraordinary diversity of dewlaps in the Anolis genus.

If you would like to read the full paper, published in the Journal of Experimental Zoology Part A, go to:http://onlinelibrary.wiley.com/doi/10.1002/jez.2076/epdf

Signals and Speciation: Do Dewlap Color Differences Predict Genetic Differences?

Dewlap and genetic differences between co-occurring Anolis distichus and A. brevirostris

Dewlap and genetic differences between Anolis distichus and A. brevirostris at sites where they co-occur on Hispaniola.

Here at Anole Annals, we’re all familiar with the replicated evolution of different anole ecomorph types in the Greater Antilles. However, divergence into these different ecomorph classes is not enough to explain how the group became so speciose on these islands. Additional factors must therefore have promoted speciation throughout the history of the group.

One potential factor is the flashy anole dewlap. Dewlap diversification across anoles has led to the remarkable array of dewlap color, pattern and size we see today. If dewlap differences did indeed drive speciation in anoles, or are involved with the maintenance of species boundaries, we might expect that as differences in dewlap color and pattern increases between species, genetic differentiation will also increase through fewer hybridization events.

In our study that just came out in the Journal of Herpetology, Rich Glor, Anthony Geneva, Sabina Noll and I set out to test this using two widespread species from the Anolis distichus species complex, A. distichus and A. brevirostris. These two species co-occur in many locations on Hispaniola and, while they often differ in dewlap color where they do co-occur (yellow with an orange patch vs. all pale yellow), in other areas, they co-occur with similarly pale dewlaps. Using mitochondrial DNA, microsatellite and AFLP data, we investigated patterns of genetic differentiation at four sites: two where the species differ in dewlap color, one where the species share the same dewlap color, and another where pale dewlapped A. brevirostris co-occurs with two A. distichus subspecies (one with a similarly pale dewlap and the other with an orange dewlap).

In general, we found that A. distichus and A. brevirostris looked like “good species,” with strong genetic differentiation and little evidence of hybridization, even at a site where they share the same dewlap color. This suggests that dewlap color differences are not associated with genetic differentiation in a manner one might expect if dewlaps were involved in the speciation process or in maintaining species boundaries. However, at the site where A. brevirostris co-occurs with two A. distichus subspecies with both similar and dissimilar dewlap colors, we found some evidence of hybridization and the species were not as highly genetically differentiated. This discrepancy suggests that site-specific factors could be influencing the dewlap’s role in speciation or maintaining species boundaries. For example, as Leo Fleishman’s and Manuel Leal’s work has shown (e.g. 1, 23), the dewlap’s effectiveness as a signal is dependent on the light environment. Further understanding about the environmental differences among our study sites, how species utilize the available light microhabitats within each site, and how the dewlap looks to anoles at each site could provide more insight into our findings.

On the other hand, perhaps we need to be looking beyond the dewlap and focusing instead on whole signaling displays. Anole behavioral displays can also be strikingly different among species (e.g. 1) and may instead be the key to understanding species diversification in Greater Antillean anoles.

Happening Now: The Latin American Congress of Herpetology

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The 11th Latin American Congress of Herpetology is underway right now at the Museo de Zoología QCAZ at Pontificia Universidad Católica del Ecuador. Although I could not attend, I have been following the meeting vicariously as attendees have been using the Twitter hashtag #latinherps to document the meeting.  From those tweets alone, it appears the meeting has featured a series of fantastic talks, including many on anoles. If you are not a Twitter user you can still follow along by clicking more below to see all tweets from the Congress. Finally to Congress attendees, if any of you are interested, it would be great to have you contribute Anole Annals posts (or even comments below) on talks from the meeting.

Continue reading Happening Now: The Latin American Congress of Herpetology

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.

If West Indian Weevils Colonized the Mainland 19 Million Years Ago, Were Norops Anoles Along for the Ride?

Exophthalmus scalaris. Credit: symbiota4.acis.ufl.edu/scan

Exophthalmus scalaris. Credit: symbiota4.acis.ufl.edu/scan

In their 2008 review  “Are islands the end of the colonisation road?” Bellemain and Ricklefs (2008) concluded that oceanic islands could be important sources of colonisation of mainland continental areas and cited anoles of the Norops clade as a notable success. There are more than 5 times as many Norops clade species in Central and northern South America as in the West Indies; the 23 extant Caribbean species in the clade are distributed in Cuba and Jamaica with one species in Grand Cayman (Nicholson et al, 2005). Data in Nicholson et al (2005) gave support to the reverse colonisation hypothesis, but did not offer specific dating for the colonisation.

New analyses of 65 species in the Exophthalmus weevil genus complex (Zhang et al 2017) have turned up results that are of significance in understanding the biogeographic history of Caribbean anole dispersal and diversification. Like anoles of the Norops clade, the weevils show reverse colonization (island-to-continent), with diversification on the mainland and diversification within the islands. The data also give some support for overwater dispersal as the factor best explaining ancient between-island distribution.

Zhang et al’s best fit biogeographic model gives an estimate of 19Ma for a jump dispersal of Exophthalmus, most likely from Hispaniola,  which went on to diversify into more than 40 species in Central America.   So – did the anoles and the weevils make their journeys to the mainland around the same time and under similar conditions? Can this weevil study and the techniques it uses to arrive at its conclusions inform anole evolution and dispersal?

References

Bellemain, E and RE Ricklefs (2008) Are islands the end of the colonisation road? Trends Ecol Evol. 2008 Aug; 23(8):461-8. doi: 0.1016/j.tree.2008.05.001. Epub 2008 Jun 26.   (Correction to citation numbering: Trends Ecol Evol. 2008 Oct; 23(10):536-7).

Nicholson, KE, RE Glor, JJ Kolbe, A Larson, S Blair Hedges, JB Losos (2005) Mainland colonization by island lizards.  Journal of Biogeography 32 (6), 929-938.

Zhang, G, U Basharat, N Matzke, NM Franz (2017) Model selection in statistical historical biogeography of Neotropical insects—The Exophthalmus genus complex (Curculionidae: Entiminae). Molecular Phylogenetics and Evolution, 109, 226-239. DOI: 10.1016/j.ympev.2016.12.039.

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: Removal of Curly-tailed Lizards Increases Survival of Urban Brown Anoles

CRodriguez_JMIH2017

Interspecific Interactions Between Two Species of Invasive Lizards in an Urban Environment; Camila Rodriguez-Barbosa and Steve Johnson

An extensive body of work has addressed the eco-evolutionary impacts of the Northern Curly-tailed Lizard (Leiocephalus carinatus) on Brown Anoles (Anolis sagrei) (much of it receiving coverage right here, here, and here on Anole Annals!). These species co-occur not only on many Caribbean islands where much of this research has taken place, but also within the urban matrix of southern Florida, where both species are introduced.

Camila Rodriguez-Barbosa and Steve Johnson investigated the impacts of curlies on brown anoles in shopping centers in southern Florida where both species were plentiful. Camila first collected baseline data on anole and curly populations at eight sites before embarking on a quest to eliminate curlies from four of her sites. Over the next four months, she removed over 300 (!) curlies from these sites, many of which had brown anole remains in their stomachs.

She found that this removal had serious consequences for brown anoles. Compared to anoles from shopping centers where curlies were unchanged, A. sagrei at removal sites experienced higher survival and consequently greater abundances. These anoles also shifted to lower perches once curlies were removed, mirroring results from previous work which show that the introduction of curlies leads to brown anoles occupying higher perches to escape this dangerous predator. Camila’s work suggests that brown anole/curly-tailed lizard interactions may be similar even in very different habitats and provides a fascinating look at lizard life (and death) in the urban sprawl of southern Florida.

JMIH 2017: Brown Anole Reproductive Output Varies Seasonally

TMitchell_JMIH2017

Tim Mitchell, Josh Hall, and Daniel Warner: Seasonal Shifts in Anolis sagrei Reproduction Invoke Challenges for Scientific Reproducibility

Sometimes a scientist just needs hundreds of hatchling anoles for an experiment. Tim Mitchell found himself in this position recently, and, like a good lizard ecologist, he started breeding colonies of anoles in the lab to produce eggs to incubate until hatching. As he created three different breeding colonies from brown anoles (Anolis sagrei) in central Florida, one each in February, June, and September, Tim found that he had also created an ideal situation in which to examine how the reproductive condition and output of brown anoles varies across the breeding season.

Tim, along with his coauthors Josh Hall and Dan Warner, found that females produced eggs with significantly greater mass later in the breeding season. These eggs took longer to produce than those earlier in the year (a greater interclutch interval), and the eggs resulted in hatchlings that had higher mass in relation to the weight of their eggs. These reproductive differences remained even after accounting for the fact that female anoles were also larger and heavier later in the year.

These findings suggest that female A. sagrei may shift their reproductive effort from producing a higher quantity of eggs (i.e., more, smaller eggs resulting in smaller hatchlings) in the beginning of the breeding season, to producing higher quality eggs (i.e., fewer, larger eggs resulting in larger offspring) later in the breeding season. Tim’s findings also stress the importance of investigating and accounting for seasonal differences when examining reproductive output in 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!

Evolution 2017: Anoles and Ameivas Have Similar Gut Microbiomes

Late Breaking: one last Evolution 2017 post!  Last weekend during the Evolution meeting, I had a chance to chat with Iris Holmes (Ph.D. student, University of Michigan) about the poster she presented. Initially not on our watch list because of the lack of “anole” in the description, my eye caught the dewlapping lizard perched at the top of her poster from across the room.

2017-06-25 19.53.04

Iris presented her work on gut microbiomes of two groups of lizards: anoles and ameivas. She wanted to know if different taxa have different gut microbiomes and to what extent diet influences bacterial composition of gut microbiomes. Her collaborator (Ivan Monagan) collected scat samples from 22 Anolis dollfusianus and 9 Ameiva from an agricultural area in the Soconosco region of Chiapas, Mexico. Together, they then sequenced both the gut bacteria and the digesting prey with two 16S primers. Iris chose to target the prey as well because she wanted to know if they were eating different things and how different stages of digestion influence gut bacteria communities.

Iris found that there were no clear differences between the gut microbiomes of anoles and ameivas. Both species had gut microbiomes dominated by three main phyla: Proteobacteria, Firmicutes, and Bacteroidetes. Little is currently known about how these bacteria relate to digestion and health in reptiles, but Iris commented that we can make some guesses based on studies in other taxa. Proteobacteria are a disease indicator in mammals, but appear to be normal in reptiles and birds. Firmicutes and Bacteroidetes are both important for digestion of carbohydrates and fats (respectively) in mammals. Iris found that there was a loose correlation between the amount of prey consumed and the abundance of Bacteroidetes, suggesting these bacteria also play a role in digestion in lizards. She also found that there was an apparent tradeoff between the Proteobacteria and the two other groups – sequence abundance of proteobacteria was negatively correlated with abundance of Bacteroidetes and Firmicutes. Overall, this is an interesting first step in understanding the gut microbiomes of reptiles and how they differ (or don’t) between groups.

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.

Subfossil Record Reveals Human Impacts on a Lesser Antillean Endemic Anole

Figure 2: Landmarks (black point circled in white) and sliding landmarks (black points) used in the geometric morphometric analysis.

Figure 1. Landmarks (black point circled in white) and sliding landmarks (black points) used in the geometric morphometric analysis.

The knowledge of the past squamate fauna of the Guadeloupe islands (French Lesser Antilles) dramatically increased these last years in the framework of two European paleontological research programs. New archaeological and paleontological excavations (about which I previously talked) have been conducted and led to the discovery of thousands of squamate remains allowing to complete the pioneering works conducted by G. K. Pregill in the 90’s (Pregill et al., 1994). Results obtained on iguanas (Bochaton et al., 2016b), galliwasps (Bochaton et al., 2016a), ameivas (Bochaton et al., 2017a) and other taxa (Bailon et al., 2015; Bochaton et al., 2015; Boudadi-Maligne et al., 2016) point to high extirpation and extinction rates, mainly taking place during the last centuries after the European colonization of the archipelago and probably in relation to introduction of exogenous competitors and predators, as well as the practice of intensive agriculture.

In the middle of all of these extinctions, anoles, which are still very common in Guadeloupe, appeared to be kind of indestructible and were apparently not impacted at all by recent anthropogenic disturbances. However, the study of a huge assemblage of anole remains from Marie-Galante Island dated from Late Pleistocene to the 14th century reveals that this first impression was far from true.

Nearly 30,000 anole remains coming from several deposits were investigated using a combination of morphological and morphometric approaches. Size estimations (see Bochaton, 2016; Bochaton and Kemp, 2017) indicate that whatever the stratigraphic layer they come from, fully mature individuals range in three groups of Snout-Vent Length (SVL) size (Figure 2).

Figure 2.  SVL reconstructed on the basis of fully mature humeri (N = 66) with the results of a mixture analysis indicating a trimodal distribution. MTMS1, minimal theoretical maximal size obtained from the smallest fully mature humerus; MTMS 2, minimal theoretical maximal size obtained from the largest immature humerus; MTMS 3, minimal theoretical maximal size obtained from the smallest mature humerus included in the intermediately sized group.

Figure 2. SVL reconstructed on the basis of fully mature humeri (N = 66) with the results of a mixture analysis indicating a trimodal distribution. MTMS1, minimal theoretical maximal size obtained from the smallest fully mature humerus; MTMS 2, minimal theoretical maximal size obtained from the largest immature humerus; MTMS 3, minimal theoretical maximal size obtained from the smallest mature humerus included in the intermediately sized group.

These SVLs partly match those of the females (max 75mm SVL) and males (max 120 mm SVL) of the modern solitary Marie-Galante anole (Anolis ferreus). However, a third group of fossil specimens of very large size reaching 150mm SVL also occurred in the deposits and has no modern counterpart on the island. Still, morphological analysis indicates that these large specimens were also A. ferreus. A geometric morphometric analysis (Figure 1, above) was also conducted on dentaries of Marie-Galant fossils and included in a modern sample of Lesser Antillean anoles.
Figure 3. Two first axes of the PCA conducted on shape data collected for fossil and modern A. ferreus dentaries showing a diminution of morphological variability between fossil and modern anoles.

Figure 3. Two first axes of the PCA conducted on shape data collected for fossil and modern A. ferreus dentaries showing a diminution of morphological variability between fossil and modern anoles.

This analysis reveals a strong heterogeneity of the morphology of the dentary mostly depending of their size (allometry). The three fossil size groups are however closer to modern A. ferreus than to any other modern taxa and are linked by a common allometric relationship between their size and shape which differs from modern A. ferreus. The morphological variability of the fossil dentaries is also higher than that of modern A. ferreus (Figure 3).

These results indicate that all fossils are likely to correspond to A. ferreus. However, fossil representatives are more morphologically variable in terms of size, shape, and allometry than modern A. ferreus.The morphology of fossil A. ferreus remained stable during more than 30,000 years before an abrupt change that occurred during the last centuries. There is, however, a void of fossil data during the modern period which precludes linking this reduction of morphological variability between fossil and modern A. ferreus to a distinct event. Yet, this phenomenon is contemporaneous to the numerous extinction events documented on Marie-Galante and is thus very likely to be also related to the anthropization of the island.

This study also provides a strong argument again the hypothesis of the past occurrence of a second anole species smaller than modern A. ferreus on Marie-Galante and used to explain the large size reached nowadays by this insular solitary anole.

More details can be found in the publication of this work:

Bochaton, C., S. Bailon, A. Herrel, S. Grouard, I. Ineich, A. Tresset, and R. Cornette. 2017b. Human impacts reduce morphological diversity in an insular species of lizard. Proc. R. Soc. B 284:20170921.

References

Bailon, S., C. Bochaton, and A. Lenoble. 2015. New data on Pleistocene and Holocene herpetofauna of Marie-Galante (Blanchard Cave, Guadeloupe Islands, French West Indies): Insular faunal turnover and human impact. Quaternary Science Reviews 128:127–137.

Bochaton, C. 2016. Describing archaeological Iguana Laurenti, 1768 (Squamata: Iguanidae) populations: size and skeletal maturity. International Journal of Osteoarchaeology 26:716–724.

Bochaton, C., and M. E. Kemp. 2017. Reconstructing the body sizes of Quaternary lizards using Pholidoscelis Fitzinger, 1843 and Anolis Daudin, 1802 as case studies. Journal of Vertebrate Paleontology 37:e1239626.

Bochaton, C., R. Boistel, F. Cassagrande, S. Grouard, and S. Bailon. 2016a. A fossil Diploglossus (Squamata, Anguidae) lizard from Basse-Terre and Grande-Terre islands (Guadeloupe, French West-Indies). Scientific Report 28475:1–12.

Bochaton, C., S. Grouard, R. Cornette, I. Ineich, A. Tresset, and S. Bailon. 2015. Fossil and subfossil herpetofauna from Cadet 2 Cave (Marie-Galante, Guadeloupe Islands, F. W. I.): Evolution of an insular herpetofauna since the Late Pleistocene. Comptes Rendus Palévol 14:101–110.

Bochaton, C., S. Bailon, I. Ineich, M. Breuil, A. Tresset, and S. Grouard. 2016b. From a thriving past to an uncertain future: Zooarchaeological evidence of two millennia of human impact on a large emblematic lizard (Iguana delicatissima) on the Guadeloupe Islands (French West Indies). Quaternary Science Reviews 150:172–183.

Bochaton, C., R. Boistel, S. Grouard, I. Ineich, A. Tresset, and S. Bailon. 2017a. Evolution, diversity and interactions with past human populations of recently extinct Pholidoscelis lizards (Squamata: Teiidae) from the Guadeloupe Islands (French West-Indies). Historical Biology.

Boudadi-Maligne, M., S. Bailon, C. Bochaton, F. Cassagrande, S. Grouard, N. Serrand, and A. Lenoble. 2016. Evidence for historical human-induced extinctions of vertebrate species on La Désirade (French West Indies). Quaternary Research 85:54–65.

Pregill, G. K., D. W. Steadman, and D. R. Watters. 1994. Late Quaternary vertebrate faunas of the Lesser Antilles: historical components of Caribbean biogeography. Bulletin of Carnegie Museum of Natural History 30:1–51.

Evolution 2017: Thermoregulation Simultaneously Impedes and Impels Evolution

Major Anole Annals contributor Martha Muñoz gave a brilliant talk at the Evolution meeting  as an awardee of a well-deserved ‘Young Investigator’ award from the American Society of Naturalists. In her talk, Muñoz discussed how two classic papers by Janzen (1967) and Huey et al. (2003) influenced the way she thinks about the interplay between behavior, physiology, and evolution. Not surprisingly, Anolis lizards played a leading role in her exposition.

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Martha Muñoz introduces the Cybotoid Anoles.

Martha’s talk, entitled “Janzen’s hypothesis meets the Bogert effect: a synthesis nearly 100 years in the making”, started by describing Janzen’s hypothesis. In short, Janzen (1967) predicted that physiological differences among populations across altitudinal bands would be stronger in tropical mountains than in temperate ones. The main argument was that populations can more easily adapt to a given temperature range in tropical environments because these ranges are stable throughout the year, whereas the temperatures of different altitudinal bands overlap more in temperate areas due to seasonal variation.

Martha explains how daytime and nighttime temperatures in the tropics mirror seasonal patterns in temperate and tropical climates.

Martha explains how day and night temperatures in the tropics mirror seasonal patterns in temperate and tropical climates.

Expanding on Janzen’s idea, Muñoz hypothesized that diurnal and nocturnal temperature variation in a single tropical mountain could also generate differences in physiological divergence among lowland and highland populations. The idea was that daytime temperatures were variable with overlap across elevation (similar to the seasonal picture in temperate areas) and nighttime temperatures were more constant and differed between elevations (similar to the seasonal picture in tropical areas).

To test this, Martha sampled populations in the Dominican Republic at sites ranging in elevation from sea level to 2400m. She then analyzed heat and cold tolerance of several species of anoles from the Anolis cybotes group. Results on cold tolerance (CT min) seem to agree with Janzen’s hypothesis: cold tolerance strongly covaries with altitude at night, with higher elevation populations having lower critical thermal minimums. Interestingly, however, heat tolerance (measured as CT max) was not at all associated with elevation.

Why did Janzen’s hypothesis fail to explain the evolution of heat tolerance across the altitudinal range? This question led to a key point of Muñoz’s talk: Janzen’s hypothesis might fail to predict evolution of CT max because it is agnostic about behavior. In the case of ‘cybotoid’ anoles, lizards from different altitudes could actively adjust their habitat use to achieve optimal temperatures. As a consequence, thermoregulatory behavior could forestall evolution of physiology in heat tolerance. By studying habitat use across different elevations, Muñoz showed that, although anoles behave as thermo-conformers at low elevations, they clearly thermoregulate at high elevations. In other words, anoles were at similar temperatures to the average available substrates in lowlands but their body temperatures were significantly higher than perches at higher elevation.

Martha explains how the thermoregulation can lead to slower evolution in a trait (the Bogert effect)

Martha explains how the thermoregulation can lead to slower evolution in a trait (the Bogert effect)

This was at least partially explained by habitat use differences: anoles at high elevations perched most frequently on boulders, which are on average about 5º C warmer than trees –the most used substrate in low altitudes. In fact, 90% of the trees Martha sampled at these high elevation sites were lower in temperature than the preferred temperature of the lizards! These data indicate that anoles from the A. cybotes group have buffered natural selection in physiology by means of behavioral adjustments –a phenomenon known as the Bogert effect (also called behavioral inertia; Bogert 1949).

Finally, the talk had a third part. And yes, it got even more interesting! Due to the observed habitat use differences in high latitudes, Muñoz and her collaborators predicted that although behavior could buffer physiological evolution on heat tolerance, it could spur evolutionary change in ecologically-relevant morphological traits (the behavioral drive hypothesis). Specifically, they predicted that increased use of boulders (for thermoregulation) at high elevations should drive morphological shifts in traits related to boulder use: head and limb morphology. They found evidence for these hypothesized morphological differences: high elevation lizards had higher head heights and longer hindlimb,  in agreement with functional predictions. Finally, a captive breeding experiment confirmed that these differences were the consequence of genetic changes and not simply due to developmental plasticity.

Martha’s research is a great example of how, as Huey said, studying behavior can be crucial to improve our understanding of evolutionary processes. We are looking forward to hear about future research from the Muñoz lab, which is about to open at Virginia Tech!

 

References:
Janzen, D.H. 1967. Why mountain passes are higher in the tropics. American Naturalist 101:233–249

Huey, R.B., Hertz, P.E., Sinervo, B. 2003. Behavioral drive versus behavioral inertia in evolution: a null model approach. American Naturalist 161: 357–366.

Muñoz, M.M. et al. 2014b. Evolutionary stasis and lability in thermal physiology in a group of tropical lizards. Proc. R. Soc. B 281: 20132433.

Muñoz, M.M., Losos, J.B. Thermoregulation simultaneously promotes and forestalls evolution in a tropical lizard. (Accepted pending minor revision). American Naturalist.

Evolution 2017: Spatial Structuring of Urban Green Anoles

In his Masters thesis conducted in Simon Lailvaux’s lab at the University of New Orleans and presented this week at Evolution 2017, David Weber used a multiyear data set of Anolis carolinensis lizards’ locations and morphology as well as a DNA-based pedigree to investigate the effects of body size and relatedness on the spatial distribution of these lizards. Specifically, he set out to test three hypotheses: first, are males’ home ranges larger than females’ home ranges? Second, are bigger males more likely to be surrounded by smaller males that are related to them? And third, is there any evidence for the inheritance of home ranges from parent to offspring?

Anolis carolinensis dewlapping. Photo by Cowenby available on Wikipedia.

Anolis carolinensis dewlapping. Photo by Cowenby available on Wikipedia.

Lizard locations were sampled in an urban New Orleans park twice a year, in the fall and in the spring, from 2010 to 2015. The dataset included over 800 individuals, and what struck me most about these data was that, of these 800+ individuals, fewer than 100 were observed often enough to estimate home range volumes–death and dispersal can rule these lizards’ lives! Male and female home range volumes did not differ significantly (and the trend was in the direction of females moving over larger areas, which concurs with data from Robert Gordon’s 1956 thesis on green anoles, but with little else, I think). Curiously, smaller neighbours of the biggest males were less related to them than were males found farther away, suggesting that male anoles don’t preferentially tolerate their kin over non-kin. And though philopatry  (aka site fidelity aka staying the same place) was rare overall, females were a bit more likely to co-occur with their male offspring than males were. In a result that conforms to traditional wisdom, Weber found that the biggest males in the site seemed to avoid each other, potentially spacing themselves as far apart as possible.

Following a kind shout-out to my and Jonathan Losos’ recent paper on Anolis territoriality or the lack thereof, Weber chose to interpret his results as making sense only outside of a territorial framework. Unsurprisingly, I concur with this decision entirely, and am excited to see where Weber goes with this idea in the publications resulting from this mammoth dataset!

Evolution 2017: Integrating Ecological, Antagonistic and Reproductive Character Displacement

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The arrival of an outsider that overlaps in resource use and habitat with local species can lead to intense competition between the two. A result of this competition can be character displacement, where traits of the species (one or both) change in sympatric populations (where the co-occur), but not in allopatric populations. Claire Dufour (Post-Doctoral researcher at Harvard University) presented her work on character displacement for two anole species on the island of  Dominica: the native Anolis oculatus and the introduced Anolis cristatellus. Her objective was to integrate ecological, antagonistic and reproductive character displacement. Specifically, she tested whether competition  between these new island-mates leads to changes in habitat use, morphology, and display behavior.

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Location of populations of the introduced A. cristatellus with the sampled area, Calibishie inset

Claire compared allopatric populations of the two species with sympatric populations in the northern area of the island in Calibishie, where Anolis cristatellus has been present for two years. She found that in sympatry, both morphological and behavioral shifts have occurred. In sympatry, Anolis oculatus perched higher and had shorter limbs. She also found differences in display behavior, which she tested with an anole robot programmed to dewlap and do push-ups. This experiment showed that in sympatry, Anolis cristatellus dewlapped less, but Anolis oculatus does not alter its display behavior. Future work will test for reproductive character displacement and contrast populations where Anolis cristatellus has been present for a longer time span.

Evolution 2017: Sensory Drive and Lizard Adaptive Radiation

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The Sensory Drive hypothesis predicts that species will evolve communication signals that are effective in the particular light environment in which they occur. Anolis lizards are an excellent example: in dark habitats, they tend to have light-colored, highly reflective (and transmissive) dewlaps that are usually yellow or white in color, whereas in bright, open environs, dewlaps tend toward blue, black, orange or red. However, demonstrating that these dewlaps are actually effective at being visible in their particular habitats has proven surprisingly challenging.

Leo Fleishman has been a leader in this area and in a talk at the sensory ecology symposium at the evolution meetings, he presented new and exciting developments. First, in line with previous work, he showed that the spectral reflectance/transmittance of dewlaps is not particularly well-matched to that of the background. Rather, the same colored dewlaps appear to be maximally contrasting with the radiance of the background across all habitats:  basically all habitats have mostly green backgrounds, and red or orange stands out the best against the green background, no matter what the habitat.  So much for sensory drive, it would seem!

But more recent work saves the day: it turns out that habitats differ in the total intensity of light (number of photons coming down) they receive and that, furthermore, across species, dewlap intensity (total photons reflected and/or transmitted) is negatively related to habitat intensity (with one notable outlier, the enigmatic A. gundlachi). Under the relatively low light conditions of forest shade or partial shade, color discrimination becomes more difficult, and colors such as red and orange and other dark colors do not stand out well against the background, because they simply do not emit enough photons to efficiently drive color vision.  Yellow or white works better. Conversely, in intense light environments, there is enough light to easily see the darker colors, and these stand out well against the green background. Moreover, behavioral experiments confirm that in bright light conditions red stimuli are most visible against a green background, whereas in low light yellow stimuli are more visible.  Thus, even though most Anolis habitats have similar spectral properties, differences in total light intensity strongly influence what colors are most effective, and thus appear to have played a major role in the shaping the evolution of dewlap colors.

Leo Fleishman discusses color space in 4-dimensions, corresponding to the four cones in the anole eye. For each species, red dots are color of the dewlap and green dots are the color of the background, indicating that dewlaps stand out against their background.

Leo Fleishman discusses color space in four dimensions, corresponding to the four cones in the anole eye. For each species, red dots are color of the dewlap and green dots are the color of the background, indicating that dewlaps stand out against their background.

Evolution 2017: Introduced Miami Anoles Exhibit Character Displacement

Bright and early on the last day of the annual Evolution meeting, James Stroud (Florida International University) presented his work on character displacement in novel communities of introduced anoles in Miami. In this elegant use of a natural experiment, James looked at the novel co-existence of two anoles in their introduced range and wondered if character displacement was occurring as predicted when two ecologically similar species are found in sympatry. Specifically, James wanted to know if Anolis cristatellus and Anolis sagrei would shift their habitat use when in sympatry, resulting in correlated shifts in morphology. These species are both trunk-ground anoles of roughly the same body size. They are native to Cuba/Bahamas and Puerto Rico (respectively) and are diverged by ~50 million years.

James hypothesized that in their introduced range in Florida, these two species would diverge ecologically in sympatry but be more similar in allopatry. He found that in allopatry, both species attained similar relative abundances and perched at similar heights. However, in sympatry, both decline in relative abundance suggesting that these species are interacting strongly with one another. Even more interesting, in sympatry A. sagrei perches lower and spends more time on the ground than it does in allopatry, while A. cristatellus perches higher!

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Next James hypothesized that these ecological shifts could lead to shifts in morphology. If A. sagrei is spending more time on the ground, perhaps longer limbs would be favored. Similarly, if A. cristatellus is spending more time higher up in the trees, perhaps there would be selection for stickier toepads. As predicted, A. sagrei had longer forelimbs and hindlimbs in sympatry. However, he did not find any difference in toepad morphology between sympatric and allopatric populations of A. cristatellus. Instead, he observed that A. cristatellus in sympatry with A. sagrei had significantly smaller heads.

James ended by wondering if alternative behavioral and social mechanisms may drive these observed shifts in head morphology. Either way, this case study provides an interesting insight into how a complex range of adaptive responses can result from a seemingly simple ecological interaction.

Evolution 2017: Experimentally Testing Perch Choice in Urban and Forest Lizards

Cities and urban areas are expanding rapidly around the world, altering the environment and creating very different ecological and selective pressures for organisms that live in urban habitats. A few of the most striking differences between urban and natural habitats are higher temperatures and a huge increase in artificial substrates like the walls of buildings. These artificial substrates (e.g., metal, concrete) are not only significantly smoother than natural (i.e., trees) substrates, but also absorb, retain, and radiate heat differently. Consequently, organisms may alter their behavior to better deal with these and other challenges of city life. Since anoles cannot internally regulate their temperature, behavioral shifts may be driven by perch substrate properties, temperature, or some interaction of the two.

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Kevin Aviles-Rodriguez (U. Mass. Boston) addressed this question in urban Anolis cristatellus in San Juan, Puerto Rico. He created experimental enclosures in which each wall was a different substrate: wood, plastic, painted cement, and metal. He placed individual lizards into the enclosures and observed which wall they were perched on throughout the day. He also recorded the temperature of each wall, to determine how perch temperature of each substrate type influenced perch choice. Aviles-Rodriguez conducted this experiment in both urban and forest populations, and predicted that urban lizards would use artificial substrates more readily than forest lizards.

Interestingly, he did not find that to be the case – lizards from both urban and forest habitats used bark much more than any other surface. However, when lizards did use artificial substrates, they tended to use metal and cement when these perches were cooler, suggesting that perch temperature is a factor in perch choice. Aviles-Rodriguez plans to test these hypotheses more thoroughly by conducting additional experiments across more urban replicates to see if the same pattern emerges. He also plans to experimentally control the temperatures of different perch substrates in his enclosures to see whether lizard choices are primarily driven by perch substrate or temperature.