Category: New Research Page 9 of 66

SICB 2019: The Life and Death of an Extralimital Population of Invasive Brown Anoles

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On January 6, 2019

In New Research

Brown anoles are invasive throughout the southeastern United States and are often transported via the nursery trade.

As invasive species expand across landscapes, they may engage in new interactions including with native competitors and prey as well as encountering novel environmental conditions such as different temperatures or patterns of rainfall. It is often difficult to observe the process of how invasive species which are dispersing across landscapes are affected by these novel conditions, because it may be difficult to find edge populations of invaders, and those extralimital populations which do not survive may have disappeared before scientists can observe them.

In southern Florida, many anole species have been introduced and are expanding their ranges, perhaps none more prolifically so than the brown anole (Anolis sagrei). In the past 75 years or so, brown anoles have occupied all of peninsular Florida, the eastern seaboard of Georgia, and Gulf Coast habitats through Louisiana. Many of these expansions are thought to occur via hitchhikers on cars or via the nursery trade, in which potted plants with adults or eggs are transported to new areas. These introductions may fail for many reasons (e.g., inhospitable environments, low numbers of colonizers, intentional extirpation by humans), but these processes of dispersal, establishment, and extirpation are difficult to study. Dan Warner, a professor at Auburn University, took advantage of a known extralimital population of brown anoles in a greenhouse in central Alabama to study the survival of a population created through this type of dispersal.

This population of anoles existed well north of its continuous invasive range in the United States and was exposed to much colder winter conditions than other studied populations.  It was present at the greenhouse from at least 2006, and so survived for at least 10 generations, long enough for adaptation to these novel thermal conditions to potentially occur. Working with a team of undergraduates, graduate students, and post-docs, Dan assessed the thermal conditions in the greenhouse environment, conducted mark-recapture studies of the population, and measured thermal tolerances of lizards.

Dr. Amélie Fargevieille and Jenna Pruett representing the Warner Lab at SICB 2019.

At SICB 2019, Dr. Amélie Fargevieille and Jenna Pruett presented results from the study, showing that the greenhouse population included all life stages of lizards and reached a total size of >1000 individuals. While one might expect that these northern lizards would have altered critical thermal limits, the Warner lab showed that both the upper and lower thermal limits of these lizards (the temperatures at which their movements became uncoordinated), were the same as those found in lizards from warmer, southern populations. These results indicate that existence in a colder northern climate for >10 years did not lead to adaptive changes in thermal limits, perhaps due to the population occupying a thermally-buffered habitat, i.e., the greenhouse.

While hurricanes have facilitated several fascinating studies of anole adaptation (e.g., Schoener et al., 2017, Donihue et al., 2018), they may also take these opportunities away. In the case of this population, Hurricane Irma blew off the greenhouse roof in 2017 (which remained unrepaired), exposing this population to the rigors of a central Alabama winter. Multiple surveys in 2018 confirmed that there were no survivors of this previously robust population. Dataloggers confirmed that, even in the most sheltered microhabitats that remained, temperatures dropped below the critical thermal minima of brown anoles, presumably extirpating the entire population.

Recent Extinction of a Viable Tropical Lizard Population from a Temperate Area WARNER, DA*; HALL, JM; HULBERT, A; TIATRAGUL, S; PRUETT, J; MITCHELL, TS; Auburn University.

SICB 2019: Do Bark Anoles Show Behavioral Syndromes?

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On January 5, 2019

In New Research

Daisy Horr, an undergraduate researcher at Trinity University, discusses how bark anole behavior varies across several different social contexts.

Animals often use diverse behavioral repertoires to adjust to new, unexpected, or changing conditions very quickly. While it may seem like individuals could always use the best behavior for any given situation, we know that instead behaviors are often related within an individual. In other words, an individual’s behaviors are not always independent and may represent an underlying “behavioral syndrome” or correlated set of behavioral responses to related environmental conditions. These behavioral syndromes are also sometimes called “personalities” (though application of this word to animals can be a bit controversial!). So, for instance, an individual that has a “bold” behavioral syndrome might take little time to explore a new habitat or consume a novel food item more quickly, but also be more likely to stay active in the presence of a predator rather than hiding (the safer option!).

While anoles have been the focus of much behavioral research, we still lack an  understanding of the diverse behavioral phenotypes, including behavioral syndromes, which are displayed by a variety of anole species. The bark anole, Anolis distichus, is native to Hispaniola but also found in southern Florida where it has been introduced. While small, bark anoles can be quite feisty, and are known for their dramatic display behavior in the presence of male and female conspecifics.

Male bark anoles demonstrate pushup displays prior to engaging in combat.

Taking advantage of the bark anole’s willingness to put on a show, Daisy Horr, an undergraduate student and McNair Scholar in Michele Johnson’s lab at Trinity University, led a group of fellow researchers in assessing whether these anoles show behavioral syndromes. To do this, Daisy and her collaborators measured the degree to which male bark anole behaviors were repeatable across three different contexts: trials with another male present, trials with a female present, and solo trials in which no other anoles were present. They measured variables quantifying movement as well as display behaviors such as pushups and dewlap extensions during these trials. The team also wanted to see whether the measured behavioral traits were linked to morphological and physiological variables.

Daisy and colleagues found no support for the idea that behavior was linked to morphology, including size of the body, head, and dewlap, and mass of the whole body, the liver, and fat pads (structures holding fat as energy reserves), or the hematocrit of the lizards, a metric quantifying how many red cells are present in the blood. Bark anoles did show some level of behavioral consistency, however. Movement behaviors were quite repeatable even between trials with and without conspecifics. Display behaviors, however, including pushups and displays, were repeatable within, but not across contexts. This work suggests that bark anoles have consistent behavioral syndromes in some contexts. Looking forward, research into behavioral syndromes in anoles could offer insights into how behavior may vary with habitat use, ability to invade novel environments, or selection on behavior itself!

SICB 2019: Sexual Differences in Relative Lengths of Toes

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On January 5, 2019

In New Research

Today I had the pleasure of attending an excellent talk by University of Florida undergraduate Griffin McNamara. I was really impressed with the work he presented, especially for an undergraduate.

McNamara was investigating the ratio in digit length between the 2nd and 4th digits. This is interesting because in mammals, especially humans, this ratio is sex specific, with men typically having longer ring fingers than pointer fingers. A lot of research has looked into the developmental reasons for this, with a likely relationship to hormone exposure of the developing fetus. Applying these ideas to anoles makes sense because the toe of anoles are somewhat unique in lizards, as we all know here. McNamara is looking into if sexual dimorphism in 2nd and 4th digit length was also present for anoles.

McNamara wasn’t the first person to measure this in anoles, but he was the first to use cleared and stained specimens, which likely greatly improved his ability to accurately measure digit length. Interestingly, he found that the pattern was reversed, with males having longer 2nd digits, not longer 4th digits as in mammals. In addition, this pattern didn’t show up until a lizard’s teenage years, with juvenile anoles not showing a difference between the sexes. Using cell staining to visualize dividing cells, he was able to narrow down the digit discrepancy to growth in the 2nd phalanx during sexual maturity.

Suspecting that this late onset dimorphism might still be related to hormone exposure, McNamara got his fingers on some testosterone-treated female anoles from collaborators and found that they had “masculinized” digit ratios, although not as much as true males.

I thought this was a great study, combining old school cleared-and-stained approaches with cell biology and experimental endocrinology. It also opens up lots of interesting questions. Is there an adaptive reason that mammals and lizards have sexually dimorphic digit lengths? Is it just a quirk of development? Does this digit length reversal have anything to do with the fact that the shape of anoles’ rear feet is already kind of mirrored as compared to our hands?

Local Adaptation in Mainland Anole Lizards: Integrating Population History and Genome-Environment Associations

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On November 9, 2018

In Anole Genome Research, New Research

Figure 1. Anolis punctatus, South America’s coolest lowland anole – literally. Picture by Renato Recoder.

In ectothermic organisms, environmental factors such as temperature and water availability constrain physiological and behavioral performance. Therefore, the occurrence of species in varied environments may be associated with local adaptation. On the other hand, experimental studies have shown that physiological function can be highly conserved within species over broad environmental gradients, which may be associated with the homogenizing effects of population gene flow. In a recently published study, we focus on widespread South American anoles to investigate whether the occurrence of species in distinct environments is linked to local adaptation and whether population structure and history have constrained adaptive differentiation.

Based on molecular data, my collaborators and I have previously found that arboreal lizard species have independently colonized the Atlantic Forest from Amazonia, subsequently expanding southward towards subtropical regions. This is the case of Anolis ortonii and Anolis punctatus (Fig. 1), whose ranges now encompass a climatic gradient from warm and wet conditions in Amazonia to cooler and less rainy settings in the Atlantic Forest. Our new study investigates whether species establishment in distinct climates is associated with potentially adaptive genetic differentiation between populations. To this purpose, we implement genome-environment association analyses on the basis of thousands of restriction site-associated DNA markers. Moreover, to estimate levels of gene flow – a force that could oppose adaptive differentiation – we perform historical demographic inference under a genetic coalescent framework. Lastly, to characterize the climatic gradients presently occupied by A. ortonii and A. punctatus, we estimate climatic space occupancy over their ranges.

Analyses of genetic structure inferred distinct populations in Amazonia and the Atlantic Forest in both anole species (Fig. 2), suggesting that separation of these forests following a period of contact in the past has favored genetic divergence. In the two species, historical demographic analyses inferred large effective population sizes, mid-Pleistocene colonizations of the Atlantic Forest from Amazonia, and post-divergence population gene flow (Fig. 3). These results support the hypothesis of recurrent rainforest expansions that connected presently disjunct biomes in northern South America.

Figure 2. Genetic clustering based on all SNPs from Anolis ortonii (A) as well as all SNPs (B) and candidate SNPs only (C) from A. punctatus. Proportions in pie charts on maps correspond to ancestry coefficients estimated by genetic clustering analyses. Grey areas on map indicate South American rainforests. Red arrows indicate A. punctatus sample MTR 20798 from Pacaraima on the Brazil-Venezuela border in the Guiana Shield region, a locality that is climatically similar to Atlantic Forest sites (see Fig. 4); this sample is genetically more similar to eastern Amazonian samples based in the entire SNP dataset, yet more similar to Atlantic Forest samples based on the candidate SNPs only.

Figure 3. Population history (from SNAPP) and historical demographic parameters (from G-PhoCS) inferred for Anolis ortonii (A) and A. punctatus (B). Parameters are the time of coalescence between populations (in millions of years, Mya), effective population sizes (in millions of individuals, M), and migration rates (in migrants per generation, m/g). Colors of terminals correspond to genetic clusters in Fig. 2.

Genome-environment association analyses found allele frequencies of 86 SNPs in 39 loci to be significantly associated with climatic gradients in A. punctatus. Among the candidate loci, eleven uniquely mapped to known protein-coding genes in the reference genome of Anolis carolinensis; two mapped non-specifically to more than four genes; and the remaining mapped against non-coding regions, which may correspond to regions that regulate gene expression or that are physically linked to genes that underwent selection. In the case of A. ortonii, no SNPs were associated with temperature and precipitation variation across space. Constraints related to population structure and history do not seem sufficient to explain discrepant signatures of adaptation between the two anole species; instead, this discrepancy may be related to species differences in climatic space occupancy over their ranges (Fig. 4).

Figure 4. Environmental space occupancy along latitude based on climatic PC1 for Anolis ortonii and A. punctatus. Samples used in genetic analyses are indicated with a black dot. Higher PC scores correspond to drier and colder sites. Dashed line indicates the approximate region of a pronounced north-south climatic turnover in the Atlantic Forest identified by previous studies. Red arrow indicates A. punctatus sample MTR 20798 from Pacaraima, a mid-elevation site (820 m above sea level) in the Guiana Shield region that overlaps climatically with Atlantic Forest sites (horizontal axis). Note that the two species experience largely similar climates in Amazonia and the northern Atlantic Forest, yet A. punctatus occupies cooler and less humid localities that are not occupied by A. ortonii in the southern Atlantic Forest.

The candidate genes identified in A. punctatus play essential roles in energy metabolism, immunity, development, and cell signaling, providing insights about the physiological processes that may have experienced selection in response to climatic regimes. Similar to our study, other investigations of anole lizards found differences in the frequency of alleles that underlie ecologically relevant physiological processes between populations that inhabit contrasting habitats. These examples support the hypothesis that adaptation to colder climates has played an essential role in range expansions across anole taxa, including mainland and Caribbean forms that span altitudinal and latitudinal gradients.

Anolis ortonii. Spotting this cryptically colored rainforest anole is quite challenging indeed. Picture by Miguel T. Rodrigues.

This investigation illustrates how studies of adaptation on the basis of genome-environment association analyses can benefit from knowledge about the history of landscape occupation by the species under investigation. Data on population structure and history can provide insight into how gene flow and natural selection interact and shape population genetic differentiation. Moreover, information about the direction and routes of colonization of new habitats can support spatial sampling design, help to characterize landscape gradients, and support the formulation of hypotheses about how organisms have responded to environmental variation in space.

To know more:

Prates I., Penna A., Rodrigues M. T., Carnaval A. C. (2018). Local adaptation in mainland anole lizards: Integrating population history and genome-environment associations. Ecology and Evolution, early view online.

Nomenclature of Dactyloidae: Revisit and Opinions Wanted

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On October 1, 2018

In All Posts, New Research

Hi everyone. I recently received and have to determine what to do with the following paper (editor’s note, for background, see this recent post):

As an administrator and bureaucrat at Wikispecies I have to decide how to proceed with this group of reptiles. I have made a tentative start here but please realize this is a simple start easily undone.

I recall the last time this came up, in 2012. I joined the discussion at the time. However, despite my comments at the time, I did not follow splitting the genus up then.  In the end, my view is for stability and consensus. By stability, I mean the actual meaning of stability under the ICZN code, which does not apply here. But consensus could.

Why is this paper different? Well, first up, last time it was a PhyloCode paper and as such is relatively easy to ignore, as it does not submit to the rules of nomenclature. However, this time it is an ICZN compliant paper so you cannot ignore it. As stated many times, names are to considered as valid on publication or refuted–there is no ignore. So the above paper may be refuted, but not ignored.

Last time, many argued that the genus is monophyletic. This is not really an argument against splitting. It’s a position statement. The order Testudines is also monophyletic, should every turtle species (275 living species) all go back into the genus Testudo? The current genera or lack of them present are only a reference to the history of research. It does not mean it is the most suitable arrangement.

More importantly is diagnosibility. Can the new proposed genera and their inherent species be adequately diagnosed? This is a more important question.

Note that a genus with some 500 species is generally considered too big. Many writers over the years have deemed between 100-200 species about the maximum size wanted. However, this does still need to address the previous point on diagnosibility.

Another point people brought up last time was stability. Well, stability actually refers to the mononomial and whether a name can be replaced by a forgotten name. It is used as a reason to reverse priority. This is the code purpose of stability. Note that the combination first up does not have to be stable, and second is a taxonomic decision, not a nomenclatural one. Hence outside the code.

So what I am after: Basically I want to see through any commentary if the people who work on anole’s are likely to use this new nomenclature. If they are, I will adopt it at Wikispecies. That will require the moving and reorganisation of some 550 pages. I do not take that on lightly. Hence I am asking you, the people who work on anoles, first. My decision will be based on the answers I get. I do not work on anoles. I am a turtle and tortoise specialist. But I do have a job to do at Wikispecies.

For your information, I have discussed this briefly with Peter Uetz at Reptile Database also. He also was not sure what to do, but remembered the last time it came up here. So I am reaching out to all of you on this issue. I am after consensus, not stability. As I said, stability does not apply here. But I will say that to reject the nomenclatural proposals of Nicholson et al. (2018) does require a refutation. They have presented to science in good faith in a very good journal, Zootaxa. We cannot ignore this and as a taxonomist, I will not.

In advance, I thank everyone for their comments. I think this issue needs to be openly debated.

 

 

A Second Caribbean Anole Species Introduced to Brazil

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On September 7, 2018

In Introduced Anoles, New Research, Notes from the Field

 

The brown or festive anole, Anolis sagrei, is an invasive species in several countries in the Americas and Asia. This species is native to Cuba, the Bahamas, and the Cayman islands. Following introductions, A. sagrei can reach high population densities and undergo rapid range expansion. In a recently published contribution, we provide the first record of this aggressive invasive lizard in Brazil.

In 2017, we recorded specimens of A. sagrei within the limits of an International Airport in the metropolitan area of the city of Rio de Janeiro, southeastern Brazil. The observation of juveniles and mating couples suggests that the species is established locally.

The origin, geographic extent, and potential for spread of A. sagrei in Rio de Janeiro and Brazil are currently unclear. It is also unclear whether this species will be able to colonize natural habitats, such as the surrounding Atlantic Rainforest.

The establishment of brown anole populations elsewhere has led to shifts in substrate use by native anoles and promoted major shifts in the structure of local insect assemblages. As such, this species has the potential of affecting local ecological communities in Brazil. However, the effects of A. sagrei on the local fauna – including native lizards that we sampled in the area – are difficult to predict.

This is the second case of an established exotic anole species in Brazil. Populations of the Cuban green anole, Anolis porcatus, were recently detected in several sites in the Baixada Santista coastal region, state of São Paulo.

To know more:

Oliveira J.C.F., Castro T.M., Drago M.C., Vrcibradic D., Prates I. (2018). A second Caribbean anole lizard species introduced to Brazil. Herpetology Notes, 11: 761-764.

PDF available here (at the bottom of the webpage).

Evolution 2018: Sex Chromosome Evolution

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On September 4, 2018

In New Research

“Squamates  Playing Poker” – a clever depiction of sex chromosome evolution (image by Anna Minkina shared with permission from Tony Gamble; read more about the image on the Gamble lab website)

Anole Annals contributor Yann Bourgeois reports on the talk by Tony Gamble on sex chromosome evolution. While this talk wasn’t specifically about anoles, our favorite lizards are no stranger to this topic, as discussed previously here on Anole Annals. Gamble builds on his previous work in an impressive analysis of sex chromosome evolution across squamates and snakes. We can look past the anoles taking the back-seat on this one because the talk was fascinating and sure to be of interest to readers here. Yann Bourgeois reports:

How sex chromosomes originate is one of the most intriguing questions of evolutionary biology. It is also a complex one, as the mechanisms that lead to their formation are not clearly understood and our knowledge is mostly based on model species that are not necessarily representative (most of them have strongly heteromorphic sex chromosomes). It is generally thought that sex chromosomes emerge as new alleles at a sex-determining gene stop recombining with each other. Since sex-ratio has to reach an equilibrium, balancing selection maintains the two alleles at high frequencies, and strong linkage locks together loci involved in reproductive isolation and mating. As the two non-recombining blocks diverge they accumulate mutations that can be used to discriminate them using molecular tools. In the most extreme case, one of the two chromosomes degenerates, such as the Y chromosome in humans.

Most sex-determining systems fall into two categories: ZW systems where the male is homozygous ZZ and females are heterozygous, and the classical XY system with XY males and XX females. We know from previous research that anoles fall into the XX/XY category (although some species are XXXX/XXY).  However, in general in squamates and snakes in particular, the evolution of sex-chromosomes is poorly known. Early studies mostly focused on heteromorphic chromosomes, which are so divergent that they can easily be identified through cytogenetics. But heteromorphic sex chromosomes like those in anoles and other squamates are not necessarily visible, and other tools are needed to identify which system occurs in a given species.

In his talk, Gamble showed how to use RAD-seq or RNA-seq to identify loci associated with sex, and to discriminate between XY and ZW systems (for more information on this approach, check out his 2015 paper in Molecular Biology and Evolution). For example, in an XX system, all males will be heterozygous at sex-linked loci while all females will be homozygous at the same sites. Depth of coverage will also be twice as low at X-linked loci for males than for females as they harbor a single X chromosome. Using this set of molecular methods, Tony demonstrates that there is a high turn-over of sex-determining systems in squamates and snakes, with more than 40 transitions between ZW and XY, half of those transitions being found in geckos.

It is also possible to map those sex-associated loci to reference genomes to identify syntenic blocks that may be repeatedly recruited during sex-chromosome evolution. For example, in the crested gecko (Correlophus ciliatus), most sex-associated loci map on chicken’s chromosome 10. Some genes may have a higher likelihood to be recruited when a new sex chromosome appears, but whether this can be extended to specific syntenic blocks remains an open question. This is made even more difficult by the fact that sex-determining genes in squamates are not yet known with certainty. This ongoing work on macro-evolutionary dynamics of sex chromosomes will provide interesting findings that may be linked to the evolution of mating strategies and speciation in anoles.

Evolution 2018: Whole Genome Sequencing Sheds Light on Genetic Diversity of Green Anole

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On September 3, 2018

In New Research

Anolis carolinensis (photo by Cowenby, Wikipedia)

Whole genome sequencing approaches are rapidly becoming more accessible and gaining popularity. The development of powerful analytical tools for these data has enabled novel approaches to answering outstanding evolutionary questions. Yann Bourgeois, a post-doc at NYU- Abu Dhabi, is the first to take a whole genome approach to understand the population genomics of Anolis carolinensis in the southeastern United States. Yann presented his work in a poster at Evolution 2018 in Montpellier.

Yann sequenced 27 individuals from across the native range representing the five unique genetic clusters (Gulf Atlantic, Carolinas, North Eastern Florida, North Western Florida, South Florida). He found that the Gulf Atlantic and Carolina populations were nested within the Florida populations, supporting the hypothesis of a northward expansion from southern Florida. He was able to estimate that this colonization of regions north of Florida likely occurred in the past 100,000 years. Interestingly, he also found that this dispersal event was associated with a reduction in X chromosome diversity, suggesting that dispersal was either male biased or that there has been positive selection on the X chromosome.

Whole genome sequencing of 27 individuals from across the native range reveals population genetic structure

Taking this one step further, Yann then investigated patterns of recombination via secondary contact among the genetic clusters. Yann and his colleagues found that there has been gene flow between clusters over periods of secondary contact with interspersed periods of isolation. Limited introgression between Florida and the northern populations suggests local adaptation in the northern populations.

Yann and his colleagues have provided an interesting first look at the evolutionary history of Anolis carolinensis from a genomic perspective. The revealed patterns of expansion, reduced diversity, isolation, and secondary contact raise interesting questions about the origin of new genetic clusters (and perhaps species) and their maintenance with ongoing or periodic gene flow.

For more information on this exciting research, check out the pre-print of the manuscript.

Evolution 2018: Dominica Anoles Change Up Their Displays when Faced with New Competition

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On August 25, 2018

In Education and Anoles, Introduced Anoles, New Research, Research Methods

Claire Dufour, Postdoctoral Fellow at Harvard University, presents her research at the 2018 Joint Congress on Evolutionary Biology in Montpellier, France.

In another excellent study exploring the effects of anthropogenic activity on evolution in anoles, Postdoctoral Fellow Claire Dufour is investigating how the recent introduction of Anolis cristatellus from Puerto Rico to the island of Dominica may be driving changes in the display behavior of Anolis oculatus, a Dominica native. Specifically, Dufour is asking whether interactions between the A. cristatellus and A. oculatus are consistent with patterns of Agonistic Character Displacement, in which interference competition between the newly sympatric species results in shifts in traits affecting the rate, intensity, and outcome of interspecific aggression.

To begin, Dufour and colleagues constructed a pair of robots that mimicked the typical look and display behavior of a male A. oculatus and A. cristatellus. She then traveled across Dominica and presented over 130 wild male A. oculatus with one of the two robots, and recorded the display behavior exhibited in response. Beyond measuring the duration of the response display, Dufour also tracked the proportion of time spent by the A. oculatus engaging in any of nine specific display behaviors, such as dewlap extensions, push ups, nuchal crest presentations, and others. By repeating this experiment among populations of A. oculatus existing sympatrically with A. cristatellus, as well as populations not yet invaded by A. cristatellus, Dufour was then able to ask whether variation in display time or composition among the native anoles could be attributed to the presence of A. cristatellus. Indeed, this turned out to be the case.

Anolis oculatus living in allopatry from the introduced A. cristatellus were found to engage in longer display bouts when presented with the conspecific robot, and shorter display bouts when presented with the unfamiliar A. cristatellus robot. Alternatively, A. oculatus occupying habitats already intruded by the A. cristatellus increased the duration of time spent displaying, regardless of which robot was presented. In addition, A. oculatus were also found to alter the behavioral composition of their displays when occupying habitats shared by the introduced A. cristatellus.

Dufour and colleagues capitalized on a rare opportunity to document the very early stages of a species invasion, and in turn improve our understanding of how human-mediated species introductions can promote evolutionary change. As changes in behavior are often the first response to novel competition, these results are consistent with the criteria of Agonistic Character Displacement, and support the claim that the introduction of crested anoles in Dominica has indeed driven a shift in the behavior of native anole communities. While the consequences of these shifts on the outcome of interspecific competition are still unclear, it will be interesting to see how differences in display behavior develop over time, and further, whether these initial changes in display behavior could lead to additional shifts in behavior or morphology among these newly interacting species.

Evolution 2018: Speed Is Key for Anoles in the City

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On August 25, 2018

In Education and Anoles, New Research, Research Methods

Dr. Kristin Winchell at the 2018 Joint Congress on Evolutionary Biology

Human activity is well recognized as having evolutionary consequences, and studies on the prolific Anolis genus continue to show us just how adaptable these lizards can be. Dr. Kristin Winchell, a Postdoctoral Research Associate at Washington University in St. Louis, MO, is investigating the relationship between human activity and evolution in Puerto Rican crested anoles, with a current focus on how selection across urban habitats might be driving changes in morphology and behavior among the lizards.

In an elegantly designed study, Winchell and colleagues collected over 120 male crested anoles (Anolis cristatellus) from forests and urban areas across the island. The team then assessed the ability of these anoles to perform a series of tasks representing normal daily activities, such as sprinting and clinging. By comparing anole performance on natural substrates like wood to their performance on more urban substrates such as concrete and metal, the team determined that the lizards consistently performed better on natural substrates, yet decreased their velocity when perches were inclined. Specifically, the crested anoles sprinted at less then half of their maximum speed on painted concrete, up to 32% slower on metal compared to wood bark tracks, and as much as 34% slower when surfaces were steeply inclined.

Winchell and colleagues measured differences in limb length and toe pad morphology among urban-caught and forest-caught anoles.

In addition to performance assessments, detailed scans of toe pad and skeletal morphology were collected and analyzed, allowing Winchell to identify differences in morphological traits underlying any variation in performance. Upon comparison, the pattern was clear: lizards living in cities had significantly longer limbs, more lamellae on their front toe pads, and larger overall rear toe pads. Longer hindlimbs in particular were found to positively influence velocity across substrate types, surely a selective advantage for anoles tasked with sprinting between the amply spaced urban perches. However, the urban phenotype is not without cost, as longer forelimbs were found to negatively influence velocity on more steeply inclined surfaces, as well as increasing the lizard’s likelihood of slipping. As all urban populations measured shared these phenotypic traits, however, the advantage of increased speed seems to be worth the costs.

As rates of urbanization continue to increase, further studies examining the response of taxa adapting to urban environments will be imperative. With Winchell’s plan to explore performance and morphological differences in other anole species living across the urban-forest continuum, it will be exciting to learn how these traits are affected within species originating from other territorial and arboreal microhabitats.

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