Michele Johnson (top) and Manuel Leal (bottom). For more on the Leal lab’s march-related activities, check out the post on Chipojolab.
From the pages of Facebook. Specifically, from Paul Marcellini Photography (check out the beautiful photos on his website). Note that we previously featured another account of a nesting female hummingbird attacking an anole, in this case Anolis stratulus in the Virgin Islands.
here’s a close-up, from Marcellini’s FB page:
I stumbled onto an old video from a past trip that might interest some of you. Anolis vanzolinii, named after herpetology and samba master Paulo Vanzolini, is a poorly-known species from northern Ecuador. While this video is not the most exciting–it is only a video of one crawling on a bed–it does demonstrate almost chameleon-like qualities in its movement. On a trip where we caught quite a few Anolis proboscis, this species still stood out to me as the most interesting. Hope to see them again sometime!
Steve Arnold, snake biologist extraordinaire, has a secret love of anoles. Or at least he takes pictures of them on his travels. Here are two anoles from Pico Bonito National Park in northwestern Honduras. Anyone know what they are?
Last month I spent a week in Bocas del Toro for a marine invertebrate biology course. However, I made some obligatory terrestrial excursions in search of our favorite vertebrate, the anoles! The habitat surrounding the STRI facility was secondary forest, and anoles were most commonly seen at forest edges. On one tree I found two A. limifrons scurrying about. They both promptly flattened their bodies against the thin branches when they detected my presence. A few seconds later, I noticed that a slightly larger anole was staring right at me from several inches away. I haven’t been able to get a solid ID on this female yet, and I would appreciate any input!
The adult sex ratio is an important characteristic of a population, influencing the number of available mates in an area, the strength of sexual selection, and the evolution of mating systems. In our new paper in the Journal of Zoology, Michele Johnson and I use anoles to look at variation in sex ratios within and across species within a clade.
Photo by Michele A. Johnson
This paper had its roots when Jonathan Losos put me in touch with Michele in my first semester of grad school. Michele had compiled a massive database of detailed behavioral observations for Anolis populations and species across the Greater Antilles during her PhD on territoriality and habitat use (see Johnson et al. 2010 for more details!). While still trying to familiarize myself with the data set, I came across papers by Bob Trivers on sexual selection in anoles and his publication on the name-sake Trivers-Willard hypothesis; the combination of these topics made me curious about sex ratios and their role in sexual selection. I decided to quickly calculate the sex ratios of our localities, and given their distribution, realized that we should definitely look into this more.
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Sex ratios are generally very hard to measure in the field. You need to be certain that you haven’t had any biased sampling, or in other words, that you’ve made a fair attempt at censusing the population. This is quite difficult during short sampling periods! However, Michele conducted extended behavioral observations, and carefully tagged and monitored every individual in large habitat areas for ~3 weeks in each locality. This meant that we could be fairly confident that she had captured every individual in the population during her sampling periods, and her total counts of male and females in the population would be accurate. Even more, she had these adult sex ratios for 14 species, with some of those species being sampled at multiple localities. Given these data, we could actually both look at sex ratios across the Anolis clade, and within multiple anole species, for the first time.
We had two main questions: 1) were the sex ratios of these anole populations significantly skewed (i.e., were they very far off from a 50:50 male-to-female ratio?) and 2) did the adult sex ratio of a population correlate with the strength of sexual selection in that population? For question 2, we used two measurements of sexual size dimorphism as a proxy for the strength of sexual selection. Sexual selection generally drives an increase in sexual size dimorphism (i.e., the difference between males and females in body size), but is also thought to be related to sex ratio skew (as the more skewed a population sex ratio, the more competition for mates or mating opportunities). We predicted that species with more skewed sex ratios would show an increase in sexual size dimorphism. Given that ecomorphs are an important component of evolution in anoles, and are commonly associated with varying levels of sexual size dimorphism, we also decided to test for a correlation between sex ratio skew and ecomorph type.
We found that sex ratios varied widely across and within anoles, ranging from a very female biased 0.32 in Anolis krugi to a male biased 0.61 in Anolis smaragdinus (sex ratios are expressed as the total number of adult males divided by the total number of both adult males and females in the population). Adult sex ratios also varied between different localities within a species (we had six species with multiple localities). We found two populations with significantly skewed sex ratios (Anolis krugi and Anolis valencienni) but based on Fisher’s test of combined probabilities, the sex ratios of anoles overall are not skewed away from 50:50.
I should note, however, that it is intrinsically extremely difficult to detect a skewed sex ratio in a natural population. We’re trying to measure deviations from a 50:50 sex ratio, and this requires surprisingly high population sizes since the binomial distribution has a broad center. For instance, to detect a true underlying sex ratio of 0.4 or 0.6 (away from our null of 0.5), we would need population sizes of >780 lizards to detect a significant skew 80% of the time. This is just an illustration, but the main point is that these population sizes might not exist for a given species – and so detecting significantly skewed sex ratios might not be possible at all. This is especially difficult when looking at small or endangered populations – there sex ratio skew might be a big problem, but impossible to demonstrate statistically. The general takeaway here is that sex ratio skew in a population can be biologically important, but not statistically significant.
We then used both the categorization of the anole species by sexual size dimorphism (low or high SSD) and the measured sexual size dimorphism of each population (calculated by average male SVL divided by average female SVL, minus 1). We used both of these estimates of SSD to test whether the sex ratio of a population correlated with the sexual size dimorphism of that population, as predicted by sexual selection theory. Turns out we were completely off – there was really no correlation between sex ratio skew and measured SSD, categorical SSD, or ecomorph (see figure 1, posted below, for a visual of this lack of correlation!).
Figure 1 (from the paper) : Sex ratio versus sexual size dimorphism. Sex ratio is represented as the proportion of males among adults in the population, while sexual size dimorphism was calculated dividing the average SVL of the larger sex by the average SVL of the smaller sex, and subtracting 1 for each population. Each circle represents 1 of the 21 localities sampled in this study. The dashed line represents an equal sex ratio of 0.5. We found no relationship between sexual size dimorphism and sex ratio across the 21 localities (PGLS: adjusted R2 = −0.08, P = 0.86).
So what’s the general message here? Sexual size dimorphism does not correlate with adult sex ratios across anole species, and so the relationship between strength of sexual selection, sex ratio bias, and sexual size dimorphism may be more complicated than we initially assumed. However, anole sex ratios can range widely between species, and within populations. Given the variance within anole species, the adult sex ratio is probably a better description of a locality, or population, than an intrinsic quality of an entire species. We also think that the influence of various localized environmental factors may impact sex-specific mortality or dispersal, which in turn which cause differences between localities in adult sex ratio skew.
This is my first anole paper, and it’s really nice to see all the brainstorming and discussions put into print. It was also great to get to know and work with Michele, and learn more about her research and behavioral work in anoles (we even got to meet in person at the Evolution conference last year!). This paper was also my first small step into the world of sex ratio and sex determination theory which now forms a large part of my PhD work, so I’m very grateful for the introduction to the subject. Anyway, feel free to email us with any questions and we hope you enjoy the paper!
Paper here: Sexual selection and sex ratios in Anolis lizards
Photo by Barb Karl
Everyone who has studied anoles in the field has had the experience of an anole displaying towards him- or herself. Do anoles actually display to real predators in the field? We’ve even had one AA post reporting a test of that. But there are few observations of such displays. So we were delighted to receive the following note from Barb Karl of Leland, North Carolina:
I was mowing my lawn and was startled by a green lizard that jumped to a nearby tree. I researched what type of lizard it was since we just moved to North Carolina a short while ago and wanted to see what it was. I found that it was an anole. I felt bad that I had startled him, so put some live mealworms on the fence as a peace offering. I checked a little bit later and he was back on the fence, hopefully eating the mealworms. Then a short distance away a wren appeared in the bird feeder tray. I watched the anole, he was still on the fence and started going up and down (almost like he was doing pushups and his throat pouch would go in and out). It was like he was trying to make himself bigger so the bird would not want to mess with him. It was an awesome sight!
I spotted a second Anole on a tree a distance away from the first one. Can’t wait till they visit again. Next time I will try and catch a video if it happens again.
Tobias Uller at Lund University is studying phenotypic plasticity in anoles to address the evolutionary significance of such plasticity. He’s interviewed at David Sloan Wilson’s site, This View of Life. The whole interview is interesting, but here’s the snippet on anoles:
One of my projects, with evolutionary developmental biologist Nathalie Feiner, will test if plasticity shaped diversification of Anolis lizards. These lizards are textbook examples of an adaptive radiation because, across the Caribbean, a single species gave rise to multiple species, each locally adapted to a different habitat. We are particularly interested in limb morphology since it is a defining feature of adaptive differences between species; lizards that run around on broad surfaces, such as tree trunks, have longer limbs than those who cling onto twigs, for example.
Anolis equestris. Image used with permission of Tobias Uller.
We already know from work by Jonathan Losos and others that limb growth is plastic in Anolis. What we do not know is if evolutionary diversification of limbs took place through modification of those particular components of bones that respond to mechanical stress during growth – as would be predicted if plasticity ‘took the lead’ in evolution – or if adaptive divergence between species is unrelated to plastic responses within species. To test the concordance between plasticity and evolutionary diversity we rear a lot of lizards from several species on different surfaces and combine this with detailed measures of skeletons of very many species across the entire Anolis group.
We should also remember that plastic responses in some cases can carry over to the next generation. In experiments on water fleas, which have the advantage that they can reproduce clonally so we can rear genetically identical individuals in the lab, we will test the hypothesis that such maternal effects (or non-genetic inheritance) facilitate adaptation to new environments. In some ways, this works just like plasticity within a generation. That is, successful accommodation of environmental stressors enables populations to persist and gives natural selection something useful to work with, thereby providing directionality to evolution.
But here there is another twist that has to do with the evolution of inheritance. As populations adapt, selective removal of costs and negative side-effects should make maternal effects behave like signals, sent from mothers to tell offspring about the environment they are likely to encounter. This process, therefore, describes the evolution of a type of inheritance system.
We cannot study the conversion of an environmentally induced stress response to a detection-based inheritance system in the lab. But we can compare water flea populations that have been exposed to the same stressor, such as metals or toxins, for a different number of generations in the wild. Ultimately, this should give insights into how inheritance systems evolve and how they come to transmit information.
Aposematic warning patterns are supposed to have evolved to warn potential predators to stay away. But do they work? An experimental study at the La Selva Biological Station in Costa tested that hypothesis on common ground anoles, Anolis humilis. Baruch et al., writing in the Journal of Herpetology, presented the anoles with clay models painted in an aposematic or cryptic color. The models were dangled in front of the lizards and wiggled around, simulating a flying insect. Sure enough, the lizards went after the cryptic models nearly half the time, but almost completely ignored the orange and black ones. Aposematic patterns work!
During an excursion with Indigo Expeditions to Estación Biológica Las Guacamayas, Parque Nacional Laguna del Tigre, Guatemala, we observed the unusual behaviour of a female Lichen Anole Anolis beckeri (previously Anolis/Norops pentaprion), a rarely-studied, canopy-dwelling, anole from Central America. In a paper in Mesoamerican Herpetology, we report on observing a female A. beckeri potentially tending and guarding eggs. This is possibly also an example of oviposition site fidelity in an anole.
Seven Anolis beckeri deposited in the base of a Bromeliad. Photo: Kimberley Carter
Seven unknown lizard eggs were first discovered on 9th July 2015. The eggs were deposited in the leaves of a bromeliad plant (Bromelia sp.) roughly 5m above the ground. The lichen anole is typically a canopy-dwelling species but, luckily for us, the bromeliad was in a tree at eye level to one of the research station’s balconies! The bromeliad plant had collected water and one egg in particular, lying partially submerged, was a brown, speckled colour. Another of the eggs appeared indented, a sign of potential imminent hatching. The female A. beckeri deposited an additional egg after our return to the UK, which reflects similar egg laying pattern for Anolis where independent, single eggs are laid every 5–25 days during the breeding season (Losos, 2009).
Over the next few days there were no changes in the eggs’ shapes or colour. It wasn’t until 3 days later, on the 12th of July, that we finally witnessed the owner of these eggs: a female A. beckeri sat above the clutch on one of the fronds of the bromeliad. The anole was seen repeatedly climbing into the bromeliad, seemingly to examine the eggs. She would then lick them and exhale heavily over them (perhaps to increase airflow?), before retreating to the top of the bromeliad. She repeated this sequence of behaviours, retreating to safety up the tree and then re-emerging to check on the eggs numerous times.
Video stills of the female Anolis beckeri tending the eggs. Photos: Kimberley Carter
We recorded these behaviours on video and in photographs from a distance, to avoid disturbing the lizard. The female returned on numerous occasions to examine, lick and ‘aerate’ the eggs or to seemingly guard the eggs over the next few days but on the 14th of July the female only monitored the eggs from a distance of ca. 30 cm away and did not approach them.
We also witnessed potential predatory behaviour from a Mexican Parrot Snake (Leptophis mexicanus), On the 15th July the snake was seen in the vicinity of the clutch, perhaps attempting to prey on the adult female. See full paper for detail.
These observations offer insight into the life history and behaviour of this rarely-seen anole species. Hopefully, with the continued work of Indigo Expeditions and the guides at Estación Biológica Las Guacamayas we’ll learn more about these interesting reproductive behaviours in the future.