<img src="https://www.anoleannals.org/wp-content/uploads/2020/05/Anole-Annals-Logo-375w.png"> Anole Annals

It was a real pleasure to see Dr. Ray Huey give a presentation that was inspired by research he and his collaborators began in the 1970s on seasonality of reproduction and behavioral thermoregulation in Puerto Rican Anolis cristatellus. Almost 40 years after the publication of that work, Huey and many of the same colleagues (and some new ones) returned to the same areas in Puerto Rico to examine how very fine-scale variation in thermal environment (a few meters!) might lead to variation in reproduction. The investigators (Otero, Huey, and Gorman) studied how reproduction differed between open areas (where lizards carefully thermoregulate) and forested areas (where lizards are thermoconformers) and found striking differences between them. Females in open habitats reproduced most of the year, whereas females in the neighboring forest decreased reproductive in a much more seasonal manner. Differences were largest from October – December, with females in forested habitats essentially shutting down reproduction during those months. This finding was true at two different sites.

These striking differences in reproductive phenology are similar in magnitude to differences seen along elevational gradients, but the difference here is the scale. The females that Huey compared were literally only a few meters away from each other. One important take-home message from these data is that reproduction can vary at the microgeographic scale just as it can at larger geographic scales. While the latter type of study is now common, the former isn’t. Future work should consider how small-scale variation in microhabitat use might influence reproduction so that we can better understand how general this phenomenon is.

One final point that Huey made was how collaborations can not only be an integral part of research, but also a source of personal reward as those collaborations continue over time and result in great friendships. He encouraged young investigators to keep this in mind as they progress through their academic careers.

Editor’s note: this research project has been the subject of previous posts [1,2].

SICB 2014: Arginine Vasotocin and Social Behavior

By Jerry Husak

On January 7, 2014

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:

Decreased aggression toward a mirror.
No difference in aggression toward a size-matched male.
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.

SICB 2014: Why Curly-Tailed Lizards Curl Their Tails

By Ambika Kamath

On January 6, 2014

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.

SICB 2014: Hemiclitoris Development in Anolis distichus

Anoles display a staggering amount of phenotypic diversity, even in their genital morphology. Traditionally research has focused on characterizing the diversity and function of male genitals, or hemipenes, but females also possess paired genitals, or hemiclitorises, and yet almost nothing is known about them. In fact, female genital morphology is poorly understood across all reptiles. To date, we know that in some species hemiclitorises appear as miniaturized versions of hemipenes, whereas in other species they are unique structures. Further, the timing of sexual differentiation of genital structures appear to differ among lizard clades. Clearly, we need a broader understanding of the form, function, and evolution of female genitalia in reptiles.

In a fascinating poster, Casey Gilman, a graduate student at the University of Massachusetts, Amherst, presented her work on the development and morphology of hemiclitorises in the bark anole, Anolis distichus. Here’s the abstract:

Genitalia are extraordinarily diverse and show remarkably rapid evolution, relative to other morphological traits, across a wide range of animal taxa. Male and female genitalia in many animal groups begin as the same embryonic structures and later go through hormone-mediated differentiation. Surprisingly, little is known about the genetic mechanics of these processes. Even less is known about external genitalia differentiation in reptiles. Unlike other amniote groups, lizards and snakes possess a set of paired reproductive intromittent organs, called hemipenes. In a number of lizard species, females retain miniaturized versions of the male genitalia, called hemiclitorises. In these species, hemiclitorises can be used for taxonomic purposes, as they retain many morphological characteristics of the male genitalia, which are often species-specific. In lizards, the external genitalia of both sexes grow at the same rate until approximately halfway through embryonic development. Following this period, the hemipenes of the males continue to grow while the hemiclitorises of the females regress until they are about half the length of their male counterparts. We investigated the development of male and female external genitalia in Anolis distichus to determine the timing and patterning of growth and regression of these structures using histology, immunohistochemistry and whole mount in situ hybridization.

SICB 2014: Novel Insights into the Evolution of Cold Tolerance

Green anole eating a dronefly. Photo from Wikipedia.

The tremendous diversity in Anolis lizards is one of the major draws for researchers to work on this system. There are nearly 400 species of anoles and their distribution spans much of the New World. Most of Anolis’ distribution spans environments with very low seaonsality. One exception is Anolis carolinensis, whose range spans much of continental North America, and encompasses highly seasonal environments. Further, unlike most reptiles, A. carolinensis does not hibernate during the winter. Rather, lizards remain active during the cold North American winter months.

Today Shane Campbell-Staton, a graduate student at Harvard University, presented some of his thesis work examining how A. carolinensis adapts to the thermal environment, and how local adaptation influences patterns of gene flow. The work he presented was conducted in collaboration with Scott Edwards and Jonathan Losos at Harvard University and Zachary Cheviron and Anna Bare from the University of Illinois-Urbana Champaign.

Shane first asked whether differences in the thermal environment limit gene flow among populations of A. carolinensis. To answer this question, he examined variation in over 2000 loci for 131 individuals of A. carolinensis and its ancestor, A. porcatus, from Cuba. He leveraged the Anolis genome with double digest RADseq to discover these SNPs and used multiple matrix regression to assess the correlation between genetic distance among populations and geographic and climatic distance. He discovered a significant signal of isolation by temperature, but not isolation by geographic distance or isolation by precipation. This means that populations are likely structured by thermal habitat, and that differences in temperature among localities limit gene flow in A. carolinensis.

Next Shane asked whether there was a signal of local adaptation in physiological tolerance to the thermal environment. He measured heat tolerance (CTmax) and cold tolerance (CTmin) in nearly 200 individuals of Anolis carolinensis. He found a significant positive correlation between temperature seasonality and thermal tolerance (i.e., the difference between CTmin and CTmax), but that most (though not all) of this pattern was driven by variation in cold tolerance across habitats.

Finally, Shane wanted to understand the mechanism that limits cold tolerance for terrestrial ectotherms. Specifically, he wanted to test whether oxygen limitation plays a role in determining how cold tolerant lizards are. The oxygen limitation hypothesis suggests that the ability to transport and utilize oxygen is limited at cold temperatures, and that lizards lose their mobility at low temperatures because they can no longer effectively transport oxygen to their muscles. Under this scenario, lizards that are more tolerant cold should be more efficient at transporting oxygen at cold temperatures than less cold tolerant individuals. To test this hypothesis, he examined CTmin in lizards from different thermal extremes of the species range and found that lizards from more cold-tolerant populations (i.e.,: higher latitude) utilized less oxygen at colder temperatures. His results support the oxygen-limitation hypothesis, and suggest that lizards can achieve a greater tolerance to cold, at least in part, by becoming more efficient at transporting oxygen, thereby reducing their demand for oxygen at lower temperatures.

SICB 2014: Neural Correlates of Communication Modalities in Lizards

The six species examined by Robinson and colleagues.

Reptiles differ vastly in how they communicate. Some species are predominantly visually-oriented, whereas other species rely almost exclusively on chemical signals for communication. Despite such marked differences in communication modalities, there is surprisingly little known about how communication modalities translate into differences in neuranatomy among species. Chris Robinson, an undergraduate working with Dr. Michele Johnson at Trinity University, presented a study examining the relationship between sense perception and neural density in six species of lizards.

Chris predicted that visually oriented lizards should have larger and more densely packed neurons in two visual centers – the lateral geniculate nucleus (LGN) and the optic tectum (OT) – whereas lizards that employ chemical modalities should have a similar pattern in the nucleus sphericus of the amygdala (NS). He included three iguanid species in this study, the green anole Anolis carolinensis, the curly tail Leiocephalus carinatus, the Texas spiny lizard Sceloporus olivaceous, as well as the whiptail Aspidoscelis gularis, the skink Scincella lateralis, and the Mediterranean house gecko Hemidactylus turcicus. To determine which sensory modalities best characterized each species he performed focal behavioral observations. During these observations, he quantified the number of chemosensory behaviors (rubbing the cloaca on a substrate, licking the air or substrate) and visual behaviors (head bobbing, dewlapping, and tail curling). Chris amassed over 120 hours of behavioral observations, and 10-33 hours per species, which is no small feat.

SICB 2014: The Ecomorphology of (Some) Australian Geckos

By Ambika Kamath

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.

SICB 2014: Invasive Lizards Are ‘Bolder’ than Native Lizards

On January 4, 2014

In Introduced Anoles, New Research

The anole species examined by Davis and Johnson

The annual meeting for the Society for Integrative and Comparative Biology (SICB) has kicked off and anoles are off to a roaring start. At the first poster session of the conference this afternoon, Lauren Davis, an undergraduate student working with Dr. Michele Johnson at Trinity University, will present her work on the behavioral and neural correlates of invasive ability in anoles (poster 1.19). Davis wanted to know whether invasive anoles can be identified by specific behavioral syndromes, or suite of behaviors that are expressed across different contexts. Specifically, she wanted to know whether invasive lizards are ‘bolder’ than native lizards and, in turn, invasive lizards have larger or denser neurons in neural regions associated with boldness (i.e., the amygdala, hippocampus, and hypothalamus).

To address these questions Lauren focused on three species of anole that vary in ‘invasiveness.’ These were Anolis carolinensis, a native species, A. distichus, a ‘semi-invasive’ species, and A. sagrei, a highly invasive species. She hypothesized that more invasive anoles should be ‘bolder’, meaning that they exhibit a propensity to explore novel environments, exhibit more aggressive behavior, possess higher overall activity levels, and have more behavioral flexibility (defined below) than native range lizards.

2014 Anole Calendars 60% Off

By Jonathan Losos

On January 3, 2014