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Modifying behaviour is often an animal’s first line of defence against a changing environment. We know from Martha Muñoz’s research that high elevation relatives of Anolis cybotes—A. shrevei and A. armouri–modify their perch use to better thermoregulate in colder climates. In a talk entitled “Behavioural divergence along an altitudinal gradient in a clade of tropical lizards,” graduate student Katie Boronow investigated a number of other behavioural traits, asking whether shifting to high altitudes necessitates a suite of behavioural modifications in the cybotoid anoles.

Boronow measured basking, display, escape, and locomotor behaviour in four anole populations–a high-elevation and a low-elevation site in each of two mountain chains in the Dominican Republic. Sites differed substantially in habitat openness–high-elevation sites had a higher proportion of exposed substrate and lower canopy cover than low-elevation sites.

In both mountain chains, individuals basked more and fled more readily at high-elevation sites than at low-elevation sites.  The first result is easily attributed to variation with altitude in thermoregulation–it’s not surprising that lizards bask in direct sunshine more when it’s cold. While the differences in escape behaviour might also be driven by high-altitude lizards being thermally disadvantaged, Boronow found no differences in lizard body temperature between high- and low-elevation sites. Predation risk (as measured by attacks on clay models) also did not differ between sites at high and low elevations, so this variation in escape behaviour remains a mystery.

Given that locomotor behaviour is thought to be tied closely to ecomorph and that both high- and low-elevation cybotoids are still trunk-ground anoles, it is also unsurprising that rates of locomotion (measured by movements per minute, a common metric of foraging behaviour) did not vary by elevation. Patterns of display rates were interesting–while there was no altitudinal effect on display rate, the variation in display rate among populations of cybotoid anoles was comparable to the extent of variation seen across ecomorphs in previous studies. Boronow’s results suggest that differences in macrohabitat can be an important driver of intra-ecomorph behavioural diversification in anoles. 

Readers of the Anole Annals know that the Caribbean radiation of Anolis is a classic example of evolutionary convergence: different ecomorphs have evolved repeatedly on islands in the Greater Antilles and show convergent microhabitat use and morphology. Thus, anoles are a great candidate with which to test a different type of evolutionary convergence: convergence in the physiological mechanisms underlying behavior. If anoles do show convergence in these traits, then there should be a common relationship between physiology and behavior across distantly related species. If not, then different species are using different mechanisms to achieve similar functional outcomes. Michele Johnson of Trinity University addressed this question using a comparative approach in her talk, “The Evolution of Muscle Physiology and Social Behavior in Caribbean Anolis Lizards.”

Species of Anolis that copulate more frequently tend to have a larger RPM muscle.

Johnson’s study focused on two different behaviors: copulation rate and dewlap rate. To quantify these rates, she first collected over 1,000 hours of behavioral observations on adult males across nine different species of anole. To address the mechanistic basis of copulation behavior, she then measured the sizes of the seminiferous tubules, renal sex segments, hemipenes, and retractor penis magnus (RPM, the muscle controlling hemipene retraction). Using phylogenetically independent contrasts, she found a significant positive correlation between the mean species rate of copulation and the mean species size of the RPM, but not with any other trait. Thus, species that copulate more frequently tend to have a larger muscle controlling hemipene retraction. This result supports the hypothesis that the size of a structure is related to how frequently it’s used.

To quantify the mechanistic basis of dewlap extension, she next measured the size and muscle fiber composition of the ceratohyoid muscle (which controls dewlap extension) and androgen receptor expression. There was no correlation between ceratohyoid muscle size or fiber composition and dewlap rate. However, there is preliminary support from four species for an association between androgen receptor expression and dewlap rate. This supports the hypothesis that higher sensitivity to the sex hormone testosterone increases dewlap rate. As the project proceeds, there are plans to add a fourth measure, size of the neuromuscular junction to the study, as well as increase the number of species included.

In conclusion, there appear to be some common physiological mechanisms underlying behavior across the Anolis radiation; however, there are also many physiological traits that may be employed differently among species in the production of behavior.

While we all know that the dewlap of Anolis lizards must provide some information about the signalling lizard to receiver lizards or predators, we remain uncertain about the exact nature of this information. By measuring aspects of dewlap design as well as myriad features of Anolis sagrei locomotor, immune, and behavioural performance, Tess Driessens of the University of Antwerp has begun to unravel the web of information conveyed by the dewlap.

Driessens’ results are complex, to say the least. Different features of the male dewlap relate in un-intuitive ways to various aspects of performance. For example, dewlap brightness was inversely proportional to jumping ability as well as immunocompetence, but directly proportional to haematocrit levels. Most surprisingly, given contrary results from previous work in A. carolinensis, size-corrected bite force in males was not related to any dewlap design variable in A. sagrei. In contrast to the male dewlap, no features of the female dewlap were found to relate to any measure of performance.

Though not unique to anoles, dewlaps are a defining feature of the genus, and I’ve always been amazed at how little we actually know about what dewlaps can say about the individual lizards that bear them. Driessens’ study is an important step towards answering that question.

A majority of biomechanical studies focus on eliciting maximal performance from animals in laboratory conditions, an approach that can make it difficult to apply results from the lab towards understanding performance in nature. Jerry Husak addressed this issue in his talk entitled “Maximal locomotor performance and sprint sensitivity in green anole lizards (Anolis carolinensis).”

By measuring sprint performance on a variety of perches (two different dowel widths, as well as a broad perch with pegs functioning as obstacles) and comparing these performances to sprint performance on a broad, flat surface, Husak showed that green anoles are substantially worse at running on narrow perches and through obstacles than at running on broad, flat surfaces. This confirms that animals moving through their natural habitats are almost certainly sprinting sub-maximally–in nature, green anoles are found most often on perches even narrower than those tested.

Crucially, the morphological correlates of performance varied by perch, suggesting that fine-scale studies of selection on limb and muscle morphology in the wild will require knowledge of how often and in what circumstances lizards navigate different microhabitats and move on different substrates. Coupled with behavioural observations in the wild, this study can pave the way for a more nuanced understanding of body shape evolution in our favourite lizards.

A figure from Quinn’s poster, showing alternative possible energy budgets in green anoles (click for a better view).

Animals allocate energy that they acquire to a variety of bodily functions and activities. Some of the more important allocations are those toward metabolism and growth, though the relative allocations to these is unclear. McKenzie Quinn, an undergraduate student working with Michele Johnson at Trinity University, presented her work in the third poster session on the dynamic energy budget of green anole lizards. She quantified food intake, excretion, growth, and resting metabolic rate (RMR, the energy required for basic maintenance) of individual lizards over 40 days to create a predictive model to describe how they allocate energy. If metabolism receives a large allocation, then RMR and/or body mass are expected to be significant predictors of energy use. On the other hand, if growth is more important, then aspects of body length (snout-vent length, SVL) are expected to be better predictors.

Interestingly, she found that RMR and body mass were not included in the best model of energy use. Instead, their model building (with AIC criteria, if you’re interested) showed that a decreasing nonlinear function of SVL was the best model. This suggests that metabolic functions are a small, non-significant part of these lizards’ dynamic energy budget. This work was conducted on adult males, so it will of course be interesting to see how this approach might apply to younger individuals or females. However, this is useful information to know for those who wonder how anoles allocate energy in their daily lives.

Arginine vasotocin, the reptilian homolog to vasopressin is a potent modulator of social behavior. (photos from Wikipedia)

For many of us, hearing about arginine vasotocin (AVT), or its mammalian homolog vasopressin, conjures up memories from a physiology class about water balance and the antidiuretic effects of the vasopressin system. However, AVT is also a potent neuromodulator and neurotransmitter in the brain that has strong effects on social behavior, such as parental care and pair bonding. Although most of this behavioral research has been done in mammals and birds, it appears that AVT might have similar behavioral functions in anoles! Leslie Dunham, a graduate student at Georgia State University, experimentally assessed the effects of AVT on male and female green anole behavior. By comparing lizards injected with either AVT or a control solution, Dunham was able to examine the effects of AVT on aggression and courtship in males. The behavior of individuals in the two experimental groups was then assessed in the following contexts: aggression toward a mirror, aggression toward another male, and courtship toward a female. She found:

1. Decreased aggression toward a mirror.
2. No difference in aggression toward a size-matched male.
3. No difference in courtship behavior directed at a female.

AVT decreases aggression in other vertebrates, but the lack of an effect on courtship in anoles suggests that AVT may modulate behavior differently in male anoles compared to fish and birds.

But wait, there’s more! Not to be outdone by other types of vertebrates, females in the courtship trials showed some very interesting behavior. Although Dunham focused on the effects of AVT on male behavior, she also measured female behavior during the trials. She found that females displayed more toward males treated with AVT compared to control males. This was despite any detectable behavioral difference between the male treatment groups. Why is this? Although the answer is still unknown, Dunham proposed some plausible and testable hypotheses for what might be happening. First, there may be subtle changes in behavior brought about by AVT that weren’t detected. Second, there may be a role for chemical communication between the sexes during courtship that wasn’t measured. Anoles, and iguanian lizards in general, aren’t known for their reliance on chemical communication, so this possibility is sure to spark some interesting future research.

Continuing with my theme of posting about non-anoles that anolologists find interesting, here’s a summary of a fascinating poster about tail-curling in two species of Leiocephalus: L. carinatus (the famous consumer of A. sagrei in the Bahamas) and L. barahonensis. Tail-curling is known to function as a predator-deterrent signal in L. carinatus, but its potential as a social signal has remained unexplored. Bonnie Kircher, a student in Michele Johnson’s lab at Trinity University, set about rectifying this gap.

Having never seen a curly-tail myself, I was surprised to learn that these lizards exhibit a variety of tail-curling behaviours.

A figure from Bonnie Kircher’s poster describing how tail-curling was scored in this study.

By scoring the intensity of tail-curling during social encounters as well as during non-social periods, Kircher showed that tail-curling was not used as a social signal in either Leiocephalus species. In an elegant control, she demonstrated that head-bobbing was more frequent in social than in non-social contexts, thus verifying that social contexts were indeed accurately identified.

Kircher also simulated predation by approaching the lizards and observed their use of tail-curling while fleeing. A comparison of the frequency of tail-curling between disturbed and undisturbed lizards confirmed that L. carinatus uses tail-curling as a signal during encounters with potential predators. The same pattern was not observed in L. barahonensis–we therefore don’t yet know why this species curls its tail. Kircher speculates that the behaviour might have been directed at other, undetected, predators, or perhaps plays a role in lending stability to the lizard during locomotion.

This variation in the utilization of the same signal between two closely-related species points to the lability of signal use, and with almost 30 species in the genus, this system is a prime candidate for future work on signal evolution.

Though SICB 2014 is positively teeming with cool anole talks and posters, there are plenty of other lizards that are getting a lot of attention. Yesterday, I happened upon a fascinating talk by Travis Hagey,  a grad student at the University of Idaho, titled “How geckos stick in nature: ecology and biomechanics of gecko feet.”

Strophurus taenicauda, a grass-bush-like gecko. Photo by Dave Fleming.

Addressing an overflowing room, Hagey used the dramatic diversity of gecko toepads to motivate his central question–can this diversity in toepad morphology be explained by the habitat preferences and perch-use behaviour of these geckos in nature? But going down the path of ecomorphology led to a comparison with anoles: if gecko toepads correlate with their habitat, then what about gecko limb-lengths? Using relationships between limb morphology and perch-type from arboreal anoles as well as rock-dwelling skinks, Hagey left for Queensland, Australia, with three predictions:

1. Geckos with shorter limbs would perch on narrower surfaces

2. Geckos with longer limbs would perch on rocks

3. Geckos with higher clinging ability would perch on steeper perches.

Utilizing a simple measure of lizard clinging ability (the “toe detachment angle,” which is the angle of the clinging surface away from vertical at which a lizard can no longer cling), as well as measuring perch characteristics and limb morphology for 13 species of geckos, Hagey began to look at patterns of ecomorphology. He found that different species occupied dramatically different habitats, with specialization even within the arboreal niche. Here’s what he found for each prediction:

1. Contrary to expectations, lizards perching on narrower surfaces had relatively longer limbs than average.

2. Having longer upper legs, however, correlated with rock use.

3. A higher clinging ability was correlated with having longer toes and shorter limbs. There was a qualitative or clade-specific relationship between the use of vertical perches and higher clinging ability.

Pseudothecadactylus australis, a crown-giant-like gecko. Photo from www.gondwanareptileproductions.com

Hagey speculated about the relationship between perch width and limb length in geckos, where he found the opposite pattern from anoles. One distinct possibility is that geckos have, on average, shorter limbs than anoles, meaning that a relatively long-limbed gecko and a relatively short-limbed anole may actually have the same body shape. Hagey is planning a taxonomically broad comparison of body shape and perch use, and hopes to include both geckos and anoles in this dataset–an exciting prospect that could shed light on some remarkable trans-continental convergences in lizard ecomorphology.

Forget to get yourself a calendar over the holidays? Or embarrassed when someone gave you a present and you didn’t have one to reciprocate? Fear not, there’s still time to get an Anole Annals 2014 calendar, at bargain basement prices. Act now!!! Offer expires midnight tomorrow (Jan. 4). Go here, use code

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This is not Anolis roosevelti. No pictures of that species in life exist. But it probably looked pretty similar to this brown-phase Anolis cuvieri. Photo by Alejandro Sanchez.

Anolis roosevelti, the giant anole of Culebra and Vieques, is famous in anole circles. The only Caribbean species thought to possibly be extinct, the species has not been seen since 1932.

Recently I learned of a report of an expedition to Culebra to track down the wily saurian, written by noted author and mycologist Lawrence Millman. As you’ll see, the expedition was a success, but perhaps not in the way you expect.

A Hunt for the T. rex of Anole Lizards: A Trip to Puerto Rico in Search of a Giant Shrinking Reptile.

Christian Science Monitor, July 12, 2007

“Not too long ago I picked up an old travel book about Puerto Rico and read of a rare giant lizard, Anolis roosevelti, on the island of Culebra.
“Fame will visit anyone who finds this elusive creature,” the author of the book proclaimed. Since Fame had thus far given me a rather wide berth, I hopped a plane to San Juan and then a smaller plane to Culebra.
By the time I arrived on the island, the lizard had shrunk. The book had described it as four feet long, but the local Fish and Wildlife person told me that it was no more than a foot long from snout to vent – hardly competition for a T. rex. Still, A. roosevelti is a T. rex compared with other anoles, which are among the smallest of all lizards.
I also learned that this giant among anoles had not been sighted since 1932. Not officially sighted, that is. But there were anecdotal reports of it being seen in the forested areas on Monte Resaca, Culebra’s highest summit (height: 650 feet), as recently as a few years ago.
So I drove to the base of Monte Resaca and started bushwhacking.
Trusting in serendipity, I expected to see the anole in question basking on every boulder as well as ascending every gumbo-limbo tree. I was so intent on my search that I lost all sense of direction and ended up in someone’s backyard.
A Culebran tending his garden looked up at me in surprise. My usual ploy when I trespass like this is to advance confidently toward the person, shake his hand, and announce in a punctilious English accent: “Dr. Basil Withers of the British Antarctic Survey. Jolly good to meet you, old chap.”
Since this ploy would not work in the subtropics, I said, “Hello, Señor. Seen any big lagartos around here lately?”
“Sí,” the man replied. “All the time.”
“What’s their habitat?” I asked excitedly.
“In my bathroom,” he answered. He invited me in, where I saw the lagartos skittering around on the wall. They were geckos, not anoles, and they weren’t even all that big.
Serendipity had gotten me nowhere, so I got in touch with Beverly Macintyre, who knew the island’s backcountry intimately. She mentioned a particular boulder canyon on Monte Resaca, just the sort of place, she said, where a giant anole might hang out. Then she referred to recent development on Culebra; if it continued at its current breakneck pace, she said, a lot more creatures than A. roosevelti would be either endangered or extinct.
In our search for the lizard, Beverly and I entered not so much the forest primeval as the forest prickly. Ground-hugging cacti jabbed us, mesquite bushes stabbed us, saw-toothed bromeliads slashed at us, and a plant known locally as Fire Man (Tragia volubilis) delivered stings that make the stings of a stinging nettle seem positively genteel.
And to add to it, at one point I was gazing up at what turned out to be a green tree iguana and walked into a barbed wire fence.
We did not see a giant anole. We did not even see one of the small anoles that reputedly were common on the island. But near the end of our trek, we did witness this unusual sight: a man on a horse with reins in one hand and a cellphone in the other.
The next morning, as I took a respite from my search, I began noticing other curious sights. A sign in a shop window in Dewey, the island’s only town, said: “Open Some Days, Closed Others.” A road sign indicated Termina Carretera (End of Road) when, in fact, the road did not end at all.
And in the afternoon, I was sitting on Flamenco Beach when a person in an old-fashioned diving bell emerged from the sea. At the north end of the beach, there was a tank left over from the days when the US Navy used Culebra for war games; in this setting, it had a very surreal quality.
I began to think that I had fetched up on some sort of Caribbean fantasy island – an ideal habitat for, among other things, an incredible shrinking lizard.
Several days later, I still hadn’t found the anole in question. My trip was coming to an end, so I asked Teresa Tallevast, the manager of the Culebra National Wildlife Refuge, if there was any area I might have overlooked. She suggested that I check out the trail that wound down from Monte Resaca to Playa Resaca.
Soon I was hiking on this steep trail. Every once in a while I would stop and peer into the surrounding bush. At one point I thought I saw a finned reptilian tail disappear into a tangle of mesquite, but that could have been my imagination … or another iguana.
At the bottom, the trail meandered through a labyrinth of white mangroves. I looked up at the trees’ gnarled branches and then down at their arching prop roots.
Still no anole.
At last I came out on Playa Resaca, a long, yellow swath of sand where I was the only person in sight. The sun was blisteringly hot, but I didn’t go for a swim. Resaca means undertow in Spanish, and if I had gone swimming, I might have washed ashore on the west coast of Africa or, at the very least, in the Virgin Islands.
Suddenly I saw what appeared to be the tread marks of an 18-wheeler in the sand. I was outraged. But then I realized that the tread marks were actually the flipper imprints of a female leatherback turtle who’d plodded ashore the night before to lay her eggs. Weighing a thousand pounds or more, such creatures are the reptilian equivalent of giant rigs; unlike those rigs, however, leatherbacks are an endangered species. I counted myself extremely fortunate to see even the tracks of one.
And so it was that my quest for a rare reptile on Culebra ended in success.”