Just in time for the American Society of Ichthyologists and Herpetologists meeting in New Orleans next week. From the New Orleans Advocate:
It flashed across the walkway like a lightning bolt, so fast that Bob Thomas had to do a double take. In that split second six months ago, he knew they had finally arrived.
“I’d been waiting for them to arrive in my neighborhood in Metairie. What I saw moved too fast for what we’re used to around here,” said Thomas, a herpetologist who taught at Loyola University and served as the founding director of the Louisiana Nature Center.
“It could only be one thing: a brown anole, Anolis sagrei.”
You’ve seen them — the speckled brown lizards that come out of nowhere and streak across the sidewalks. They travel in hordes — tiny, large and everything in between. Careful! You’re liable to step on them if you don’t pay attention.
Thomas’ neighborhood is far from being the first to experience an invasion of brown lizards. But where did they come from? Why are they so plentiful?
“Brown anoles are an invasive species, not native to the United States,” said David Heckard, curator of reptiles and amphibians at the Audubon Institute. “They are natives to Cuba and the Bahamas and first appeared in the U.S. in Florida. From Florida, they’ve been slowly expanding their range across the Gulf Coast. They’re aggressive and competitive and have even been spotted in Taiwan. They hitch rides on plants and are spread inadvertently by plant nurseries.”
The brown anole looks a lot different than the sleek green lizards we grew up with here in New Orleans (Anolis carolinensis). Generally, A. sagrei has a more compact physique and a shorter skull. A prominent hump appears where muscles attach at the back of the skull. When the brown anole extends its orange and red dewlap (the skin flap below its chin), it looks ferocious, indeed.
By contrast, the green anole looks far friendlier, even when its rosy-hued dewlap is extended. Native to the southeastern parts of the United States (although DNA studies suggest they originated in Cuba and came here a couple of million years ago), green anoles range as far north as North Carolina and as far west as Austin, Texas. They have delicately shaped heads and long, lean bodies. They were once plentiful in New Orleans, but sightings are becoming rare.
So, are the brown anoles killing off the green anoles, fighting over territory and winning? Consuming the green anole’s food supply?
“The theory is that the brown anoles are displacing the green anoles but not necessarily replacing them,” Heckard explained. “It’s believed that green anoles are more arboreal than brown anoles, which are more terrestrial. So, green anoles are being pushed to higher elevations — up into trees and the like. It may seem as though there are fewer of them, but they’re present — you just can’t see them hiding in the leaves and up in trees.”
Simon Lailvaux, a professor in UNO’s department of biological sciences, has studied anoles since working on his doctorate and supports the displacement theory.
“In the Caribbean, where there are dozens of species of lizards, they have learned to partition the habitat and have evolved to live in a specific part of it,” Lailvaux explained. “Green anoles there are trunk/crown inhabitants, whereas brown anoles are trunk/ground inhabitants. Over the millions of years that green anoles have been in the United States, they evolved to be able to occupy the ground because they didn’t have any competition for it. So, the relatively recent invasion of brown anoles has simply forced them back up into trees where they originally lived.”
Are we sure about that? Is anybody counting?
“How can you count green lizards way up on tree trunks and in the leaves at the crowns of trees?” answered Lailvaux. “You can’t.”
According to all three scientists, both types of anoles eat the same things: insects and other invertebrates. There are plenty of those to go around here, so it’s improbable that the green anole’s food supply is in jeopardy. Luckily for the green anoles, they may have a significant competitive advantage over the invaders.
“Brown anoles are cold sensitive and can survive only in a limited temperature range. That means the population of brown anoles crashes when we get a hard freeze, and it takes forever for their numbers to recover,” Lailvaux said. “The green anole, on the other hand, has evolved to be able to withstand lower temperatures, so they won’t be bothered by a freeze. We’re seeing, though, that it is taking less and less time after a freeze for the brown anoles to recover, which means they’re already beginning to adapt.”
The mild winters of the past few years may account for the explosion in the visibility of the brown anoles. But if A. carolinensis is being replaced (not merely vertically displaced) by A. sagrei, it would be a case of a native species dying out because an invasive species outcompetes it. Should we be looking into how to reverse that trend?
“The green anole may be a nostalgic favorite, but we don’t know yet what impact the proliferation of the brown anole will have on it or on other species. The sense is, however, that it won’t be wonderful,” Thomas said.
We know too well what an invasive species can do: Witness the nutria. By consuming the marshes, the animals not only reduced storm surge protection for our area but caused the demise of other species that called the marshes home, Thomas pointed out. Without further study, there’s no way to predict if the success of the brown anole could be similarly dire for the green anole and for biodiversity.
I’m not sure I like anoles being referred to as “ditsy,” but here’s a great opportunity to create lovely anole-wear, not to mention anole curtains, anole quilts and all kinds of other anoliana.
I’m currently reading a 274 page tome called “The Biology and Biodemography of Anolis carolinensis” by Robert E. Gordon. Dating back to 1956, this impressive piece of scholarship is Gordon’s Ph.D. thesis. Gordon collected the bulk of his data in biweekly nocturnal surveys of the demography and spatial ecology of two populations of green anoles. The surveys continued for over a year, and consequently, this document is filled with insights into these lizards’ ecology.
One sentence that caught my attention was this, from page 195:
Anolis activity is primarily diurnal, although movement and feeding were observed at night under conditions of bright moonlight.
We’ve had observations of anoles feeding at artificial lights before, but have any of you night-owl herpers observed something similar under natural light?
A figure from Gordon (1956). Can we please bring back this elegant asymmetric bar graph plotting style?
Shane Campbell-Staton giving his talk at Evolution 2016
We’ve heard about the effects of polar vortexes here on Anole Annals before. The infamous 2013/2014 event brought record-breaking snow and low temperatures to the Southern U.S., leaving people and animals both a little chilled. This created the perfect opportunity for Shane Campbell-Staton to investigate the effects of such extreme events on thermal tolerance of the native Carolina Anole, Anolis carolinensis. Shane also spoke about this at SICB earlier this year, and AA contributor Martha Muñoz covered the talk pretty thoroughly here on Anole Annals. Nevertheless, I’ll summarize some key points here in case you missed it.
An unlucky lizard during the polar vortex snow storms in the South.
Shane got lucky in the sense that he had measured thermal tolerance in August 2013 for populations affected by the polar vortex, 5 months before the event. Typically, the cold arctic air is tightly constrained around the North pole, but periodically the boundaries weaken and the cool air expands southward. These events are not regular, so Shane had no idea one was coming that winter or that it would extend so far south. It was serendipitous that his study populations, 3 in Texas and 1 in Oklahoma, were impacted by the extreme weather event. This species, particularly in the Southern portion of its range, is not used to low temperatures and reports came in of anoles dying off during the storm.
Air temperatures for January 5-7, 2014, compared to the 1981-2010 average. Map by NOAA Climate.gov
So Shane returned in August of 2014 and sampled again, curious as to how this cold impacted thermal tolerance. He found that tolerance to low temperatures, measured as critical thermal minimum (CTmin), was lower in some populations after the event! Even more, the difference was greatest in the Southernmost population (Brownsville, Texas). Shane returned again in the fall of 2014 to see if this effect persisted or if it was simply a plastic response to the event. He found that the populations sampled in 2014, and presumably their offspring, still had lower critical thermal minimums. This result suggests that the extreme cold weather had caused an evolutionary shift in cold tolerance via natural selection: only the animals that could tolerate the cold temperatures survived and passed on their cold-tolerance genes. Shane went on to conduct a common garden study to verify that the trait was not simply a plastic response. He found that the lower CTmin persisted in lab-reared animals: strong evidence that these shifts had a genetic basis.
Lastly, Shane looked at the functional genomics of cold tolerance. Using liver tissues to obtain transcriptomes (representing expressed genes), he found several gene modules associated with thermal tolerance including some associated with respiratory electron transport chain, lipid metabolism, carbohydrate metabolism, and angiogenesis/blood coagulation. He also found that the gene expression patterns in the Southern populations affected by the storm resembled the Northern populations that more regularly experience cool temperatures, indicating a common genetically based adaptive response across populations.
By Pavitra Muralidhar
Adaptive radiation is one of the most intriguing processes in evolutionary biology, and anoles are one of the well-studied examples of this process. Anoles have diversified into over 400 species across the Caribbean and Central America, and contain a multitude of highly divergent morphological and behavioral types. Thanks to an impressive history of research on this clade, we now know quite a lot about the phenotypic aspects of this adaptive radiation; however, we still don’t have a good understanding of the genetic mechanisms underlying this diversity of form, physiology, and behavior. The recent advent of next-generation sequencing, and thus the ability to quickly sequence entire genomes of non-model organisms, offers a tantalizing possibility for investigating the genetic basis of adaptive radiation in Anolis.
Tollis et al., in a lightning talk at Evolution, take advantage of these new genome-sequencing techniques to approach the genetics of adaptive radiation in Anolis. To understand the genetic mechanisms underlying the adaptive radiation of anoles, they preformed de novo genome sequencing on three Anolis species (Anolis frenatus, Anolis apletophallus, and Anolis auratus), chosen to capture different sub-groups of the Anolis phylogeny. With these data, and the published genome sequence of Anolis carolinensis, they looked for patterns in the rate of evolution compared to other vertebrate groups. They also looked within the Anolis genome to detect specific genetic regions associated with selection across the anole radiation.
Tollis et al. found that, in general, anoles appear to have a high rate of molecular evolution for a vertebrate species, which may parallel the high rate of phenotypic evolution seen in this clade. In addition, Tollis et al. looked for signatures of selection across the four Anolis genomes and identified regions associated with reproduction, olfactory reception, and limb development. This last category is of special interest, given that anoles are notorious for changes in limb morphology between species and that limb morphology is one of the key components of ectomorphs in the Greater Antilles. Tollis et al. have provided a great example of using new genetic tools to approach fundamental questions about the mechanisms underlying adaptive radiation.
The invasive brown anole A. sagrei is a territorially polygynous species, and male aggressive behavior is an important trait that affects male fitness. Aggressive behavior is quite variable across individuals and populations, and can differ based on intra- and inter-specific community context. As AA regulars know, A. sagrei is also a very successful invasive species; it has been established in southern Florida for decades, and has been steadily spreading north along the gulf coast, colonizing new regions of the US. Populations at the leading edge of the range expansion experience different biotic and abiotic environments than established populations, which can lead to different selective pressures and divergence in relevant traits. Invasive populations of A. sagrei thus provide a good opportunity to explore variation in aggressive display behavior across different ecological contexts.
Julie Wiemerslage decided to take that opportunity and explore the variation in aggressive behavior across different populations of A. sagrei. In her poster “Population Differences in Territorial Aggression in the Invasive Brown Anoles, Anolis sagrei” she proposes the following two hypotheses: 1) Lizards at the leading edge of the range expansion will be more aggressive, allowing them to outcompete other species in their new range 2) Lizards at the leading edge will be less aggressive, because population densities will be lower than areas with established populations.
To test these hypotheses, Wiemerslage collected male lizards from a) native populations, b) well-established invasive populations, and c) recent invasive populations and brought them to the lab for behavioral trials. For each population, she placed pairs of males together in a cage and quantified aggressive behavioral traits including pushups, head bobs, lunges, and dewlap flashes (don’t worry, the lizards were tethered so they couldn’t actually harm one another). She found that aggression was lowest in the leading edge populations, supporting hypothesis 2. Interestingly, the most aggressive populations were the well-established invasive populations, while individuals from the native range showed an intermediate level of aggression. The cause of this pattern is unclear, though Wiemerslage suggests that more information about these source populations (such as density, community composition) will improve our understanding of the factors affecting aggressive behavior.
We as a species are rapidly changing the global environment. The changes that get the most press are those related to climate, but we are also changing the structure of environments through land development. This leads to many important questions, one of which is whether or not the novel environments that we construct can drive evolutionary change. Kristin Winchell, a graduate student in Liam Revell’s lab at UMass Boston, has been addressing this question in the Puerto Rican lizard Anolis cristatellus, which is common in urban settings. Kristin hypothesized that urban environments should select for longer legs and greater surface area of lamellae (the morphological structures on anole toes that let them grip flat surfaces). Her reasoning was that long legs should allow animals to run faster, which should be beneficial in cities where perches and refuges are further apart than in dense natural forests. Greater surface area of lamellae should be beneficial for better grip of smooth man-made surfaces. Kristin compared morphological traits of multiple pairs of urban/natural environment populations and her hypotheses were supported. Not only that, but differences between populations were maintained in individuals developed under common garden conditions, consistent with a genetic basis of the differences. You can see these results in Kristin’s excellent recent paper in Evolution. Kristin also presented some new preliminary results that directly link the morphological changes she has observed to performance on man-made surfaces. Overall, Kristin’s work indicates that urban environments can be a potent force of rapid microevolutionary change and highlights that we are not only changing the abiotic landscape of the globe, but the evolutionary landscape as well.
Researchers that are interested in ecological and evolutionary dynamics through time often make inferences about past patterns and processes using modern data, such as DNA sequences and geographic distributions of extant taxa. But this is not the only possible approach. Studies of extinct taxa and populations using fossils can provide direct measures of species distributions and abundances in the past, which are often impossible to accurately infer with modern data alone.
In her talk titled “Extinction biases and their ramifications on Caribbean lizard communities,” Melissa Kemp described her research using fossil data to characterize the former herpetofaunal community of several islands in the Caribbean. She explored the following questions linking extinction to community ecology: 1) how has extinction proceeded in the Caribbean lizard community? 2) what is the impact of species extinction on the whole community? 3) can we predict future patterns of extinction using fossil data?
To characterize past extinction patterns, Kemp measured species abundance and morphological traits of fossil remains through time in lizard communities in the Caribbean. She sought to determine whether certain taxa underwent more local extinctions, and whether extinctions were correlated with certain morphological traits. She also quantified community evenness to see how extinction events affect the whole lizard community. She found that one family, the Leiocephalidae, has gone extinct more often than others. Interestingly, in a four-species community in which Leiocephalidae went extinct, anoles went from relatively average abundance to becoming the dominant taxa, a pattern which continues to this day. Modern Leiocephalids have been shown to predate on anoles, so this community shift may have been a result of predator release. In addition, anole body sizes increased after Leiocephalid extinction, lending further support to the predator release conclusion.
After looking at historical patterns of extinction and diversity, Kemp explored whether fossil data might give us insight into current and future patterns of extinction. For example, are species that have gone extinct in some areas vulnerable to extinction in other parts of their range? And if so, what traits are causing this vulnerability? To address these questions, Kemp compared traits of extinct taxa to traits of modern successful introduced species, which are likely to have a very low risk of extinction. She found that extinct species tend to have different reproductive modes and habitats from introduced species, suggesting that these traits may have played a role in their extinctions. In addition, modern species with similar suites of traits as the extinct taxa may be more vulnerable to extinction in the future.
Kemp’s research shows that it’s not always best to leave the past behind. Fossil data enhances our understanding not only of extinct species, but of modern ecological and evolutionary processes as well.
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