Anole Annals

Sperm of Anolis sagrei. Picture by Ariel Kahrl.

Anyone who has worked with anoles in the field can tell you that during the breeding season, you can see these lizards mating pretty frequently. In fact, brown anoles are so promiscuous they have one of the highest rates of multiple paternity in vertebrates! In addition to this, females can store sperm for months at a time, which suggests that this group probably experiences a lot of sperm competition. We know from other groups that sperm competition can lead to the evolution of lots of interesting and diverse traits, but we know relatively little about how sperm competition targets these traits in anoles (though see Klaczko et al’s 2015 paper about the rate of genital evolution in anoles). 

Some of our previous work has shown that sperm size and sperm count are correlated with reproductive success in the lab, but it’s unclear how these important components of male reproductive success evolve. To explore this, we collected data on testis size (as a proxy for sperm production/sperm count), and sperm morphology (measuring the sperm head, midpiece and tail) for 26 species of anoles. We hypothesized that if testis size had a higher rate of evolution than sperm morphology, sperm competition likely targets sperm count over sperm size.

Rates of evolution of testis size, body size and sperm morphology next to an anole sperm.

In fact, we found that testis size evolves much faster than sperm morphology, confirming our hypothesis. We also found that within the sperm, the midpiece (which contains the mitochondria) evolves 2-3 times faster than the rest of the sperm cell. This is maybe unsurprising, considering that the midpiece size is correlated with reproductive success in brown anoles, and is often associated with sperm longevity and sperm velocity in other species.

You can read the pre-print from JEB below!

Kahrl, AF, Johnson, MA, and Cox, RM. 2019.Rapid evolution of testis size relative to sperm morphology suggests that postcopulatory selection targets sperm number in Anolis lizards. Journal of Evolutionary Biology.

https://onlinelibrary.wiley.com/doi/abs/10.1111/jeb.13414

Name that cover-gracing anole!

A new book on lizard behavior has an anole gracing the cover (who can guess the species?) and an all-star cast of contributors, including a number familiar to AA faithful (see Table of Contents below). The book is due out in a month, but you can go ahead and pre-order it. Sadly, it’s priced in the stratosphere: $159 for the 400 page volume. Let’s hope for a paperback edition!

Sure, they mostly live on the other side(s) of the world, they use sounds rather than dewlaps, and you mostly see them at night.

But some anoles you could only spot at night!

And geckos are mostly tropical! And there are a lot of them! And they don’t like to lay many eggs at a time – heck, some of them even have dewlaps! And they have radiated like crazy (1860 species and counting).

Want to know more? Want to tell us more?

See you in Tel Aviv, Israel, at the end of May 2019 at Gekkota Mundi II: the second conference for gecko biologists from around the world

For more details write us:  gekkotamundi19@gmail.com

or see: https://gekkotamundi-ii.weebly.com/

In a study hot off the press, Gilles de Meester and colleagues examine the phylogenetic distribution of brain size across squamates (lizards and snakes; you can find a reference and a link to the study at the bottom). In it, the authors explore the hypothesis that larger brains evolved to allow organisms to better manage environmental complexity, through enhanced cognition and behavioral flexibility. Despite years of hypothesis testing on the subject, there is no clear consensus about its validity. De Meester et al. join the quest and investigate the relationship of brain size in 171 squamate species (including 8 anoles!) to habitat type and degree of sociality. The punchline is that snakes are the pea-brains of the squamate world. Unexpectedly, there was a strong positive relationship between degree of sociality and brain size, such that solitary species had the largest brains. And, perhaps less supported but still a trend; arboreal species generally have the largest brains, while fossorial species (those that burrow and live in the leaf litter) have the smallest.

From De Meester et al.: Ancestral state reconstruction of relative brain size (residuals of the brain to body mass regression) along the nodes and branches of the phylogenetic tree of 171 species of Squamata. Sphenodon punctatus is included as an outgroup. Species with positive residuals (blue) have large brains relative to their body size, whereas species with negative residuals (yellow–red) have small brains relative to their body size. Results were visualized using the contMap function in R (package phytools; Revell, 2012) 

But, I hear you say, what of the anoles? Well, Neotropical species had the largest brains of any biogeographical region, and anoles specifically are exceptionally big brained. In fact, on delving into the supplementary material — in which De Meester et al. provide wonderful access into the brain size data that they accumulated — it reveals that Anolis stratulus, the Puerto Rican trunk-crown spotted anole, has the relatively largest brain size of any squamate!

Here is a crude figure I just whipped up from the De Meester et al. dataset. As it shows, anoles perform very well in the brain size department relative to both all squamates and within lizards specifically. Although the American green anole (A. carolinensis) does let the team down slightly…

You can read the study in full following the link below!

Gilles De Meester, Katleen Huyghe, Raoul Van Damme. 2019. Brain size, ecology and sociality: a reptilian perspective. Biological Journal of the Linnean Society, bly206.
https://doi.org/10.1093/biolinnean/bly206

From the archives. One of the greatest <i>Anole Annals</i> posts of all times, because why not?

“You’ve gotta see this!” my fiancé Mark called to me one morning.  He was outside, which could mean only one thing: a wildlife encounter was underway.  Living in a semi-rural neighborhood in Florida, you never knew what you would see, from a mated pair of Sandhill Cranes walking down the street with their young, to Gopher Tortoises excavating burrows in the front yard.

I walked downstairs to the concrete area under our elevated house where Mark was staring at something on the ground.  I looked down to see a frog (Cuban Treefrog) with the tail of an A. carolinensis protruding from its gullet.

“I knew that lizard,” Mark said forlornly.

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I wanted to share an observation of communal basking of the Green Anole (Anolis carolinensis) from the western Highland Rim of Tennessee. The locality is near the northern extent of their range in middle Tennessee. On a warm January day this winter, I observed six (6) individuals basking in close proximity along an exposed tree branch. The overwintering habitat was a south-facing road cut.

Has anyone else observed this type of “communal” basking of anoles, either in the Green Anole (Anolis carolinensis) or other species?

Shelby Irwin, a junior in Michele Johnson’s lab at Trinity University, presented a poster on her summer research in Thomas Sanger’s lab at Loyola University examining hatchling behavior in Anolis sagrei after incubation in thermally stressful conditions. In the lab, Irwin and colleagues incubated A. sagrei eggs under a standard (27°C) and elevated (34°C) thermal regimes to investigate impacts on hatchling phenotype and behavior.

It has been previously noted that thermal stress during development can affect craniofacial development, but Shelby was interested in if there was also an impact on behavior of hatchlings. After hatching, lizards from both the standard and elevated thermal regimes were run through a gambit of exploratory (prey interactions, novel object, and open-field test) and social trials (conspecific and predator interactions). They found that “hot” hatchlings were less aggressive and exhibited less exploratory behaviors. Their findings add to the growing body of research investigating the impacts of a warming world, particularly with regards to sensitive periods in thermally sensitive species.

Recent increases in non-native species introductions by humans have spurred a flurry of research examining the subsequent impacts of species invasions. However, often times non-native species introductions go unnoticed until the species is already established. When predicting the effects of a species invasion, it is important to understand how population demographics change during the colonization and establishment stages. Amélie Fargevieille addressed this issue in her talk entitled “Population demographics of an invasive lizard following experimental introduction on small islands.”

Fargevieille and colleagues released adult Anolis sagrei onto islands off the northeast coast of Florida prior to the reproductive season and monitored survival and reproduction over the first reproductive season. The total density of lizards introduced to islands were the same, but four of their islands were introduced with male-biased populations and four with female-biased populations. They then examined the survival and reproduction of the descendants of the founding populations over the next two years. They found that male-biased and female-biased founding populations did not differ in survival rates. In addition, across all islands, juveniles had the highest mortality, which suggests that the ecological factors facilitating or deterring colonization in the earliest stages following an introduction play an important role in invasion biology. Looking forward to future work from Fargevieille and colleagues in the Warner lab!

Anolis shrevei. Photograph by Miguel Landestoy.

Post-doc Vincent Farallo presented work, co-authored by Martha Muñoz, in the behavioral physiology session on the importance of incorporating physiology and behavior when assessing how species, especially montane endemics, will be impacted by climate change. Vincent and Martha compared correlative models and mechanistic niche models to better understand how climate change may impact three anoles from the island of Hispaniola, Anolis shrevei, A. armouri, and A. cybotes. When predicting future ranges of these species using correlative modeling, Farallo and Muñoz saw that the ranges of the mountain-top endemics A. shrevei and A. armouri shrink, whereas the range of the widespread species A. cybotes remains the same under future climate change predictions. Comparing these findings to mechanistic niche modeling, which uses organismal physiology and behavior to help predict future activity times within current ranges, they found that all three species will increase activity times within the mountain-top endemic ranges.

To reiterate their findings, they showed that when incorporating behavior and physiology, montane endemic species will increase potential activity time under climate change.  However, their widespread competitor will also see increased activity, indicating the montane endemics are still likely at risk, but not directly from warming temperatures.  Understanding the mechanism of species decline will be critical for mitigating the impacts of climate change.