Anole Annals

There was a lot of discussion last month about the fabulous anole goings-on at the SICB meetings. However, there were other conferences sporting important anole work over the holidays. One of them was International Plant and Animal Genome XXII, described as “the largest AG-genomics meeting in the world” and held in San Diego in early January. Perhaps not a venue at which you’d expect anole work to be discussed, but there was Poster #720:

Mining the Most Species-Rich Amniote Genus: de novo Sequencing of Three Anole Lizards for Comparative Genomic Analysis #P720

Date: Monday, January 13
10:00 am – 11:30 am

Description:

Presenters: Marc Tollis Arizona State University, Elizabeth D. Hutchins Arizona State University, Walter L. Eckalbar Arizona State University, Michael R. Crusoe Arizona State University, Catherine M. May Arizona State University, Jessica Stapley Smithsonian Tropical Research Institute, Elise Kulik Arizona State University, Matt J. Huentelman Translational Genomics Research Institute, Rebecca E. Fisher University of Arizona, Kenro Kusumi Arizona State University

P720 – Mining the Most Species-Rich Amniote Genus: de novo Sequencing of Three Anole Lizards for Comparative Genomic Analysis

The repeated evolution of morphological adaptations to specific ecological niches makes Anolis lizards a spectacular example of adaptive radiation in vertebrates, and an ideal model for comparative genomics. The complete genome of the green anole (A. carolinensis) has already provided insights to the evolution of genomic and phenotypic variation in vertebrates. A multi-species comparison within the Anolis genus would increase the power of studies seeking to understand the genomic bases of species diversification. We carried out de novo whole genome sequencing and draft assembly of three species, the grass anole (A. auratus), the bridled anole (A. frenatus), and the slender anole (A. apletophallus). Here we report some of our preliminary comparative genomic findings. Analysis of the abundance and diversity of transposable elements within these genomes has revealed repetitive landscapes typical of non-mammalian vertebrates, yet variation between Anolis species is greater than what is observed across most mammals. This may have provided a genomic environment amenable to key adaptations during the Anolis radiation. Using well-defined models such as mouse and chicken, we identified orthologous genes integral to myogenesis and limb development, and are beginning to catalogue interspecific variation in protein-coding genes and cis-regulatory motifs. Functional anatomical and histological studies are being performed to quantify the tail and hindlimb muscle groups of these species compared to A. carolinensis. Our ultimate goal is to identify the divergent alleles associated with ecological speciation, thus bridging the genotype-phenotype gap.

Read all about it in this post on Deadspin.

Update March 13, 2014: Here’s a less happy story on the same theme.

All’s well that ends well

A couple of days ago, we had a post about a poor anole frozen to death in wintry Texas. Today comes a report on Dust Tracks on the Web of another green anole incapacitated by unseasonable chill, but with a happier ending.

In species of Anolis where females have dewlaps, we know very little about exactly how females use their dewlaps. Losos (2009) describes this lamentable situation thus:

“Unfortunately, little is known about how females use their dewlaps, and the little information that is available from three species permits few generalities. Anolis carolinensis females only rarely use their dewlaps in intersexual displays (Jenssen et al., 2000), whereas female A. valencienni use their dewlaps primarily to discourage courting males, including those of other species (Hicks and Trivers, 1983). Both A. carolinensis and A. bahorucoensis females use their dewlaps in intrasexual displays (Orrell and Jenssen, 1998, 2003); in A carolinensis, females use the dewlap more at close range and less at long range in female-female interactions compared to dewlap use in male-male interactions (Jenssen et al., 2000; Orrell and Jenssen, 2003). Unfortunately, without more information on how females use their dewlaps, we will not be able to explain sexual dimorphism and dichromatism in anole dewlaps.”

Since then, Martha Muñoz has added an observation from A. armouri, but the numbers are still small.

Attempted forced copulation in Anolis cristatellus

In July 2013, I spent ten days observing A. cristatellus in Mayagüez, Puerto Rico, and can add one more species to the list of female anoles that use their dewlaps to dissuade males from mating with them. I was mapping male territories and counting male-male interactions in a park in one of Mayagüez’s fancier neighbourhoods, and came across a male chasing after a female. I sat down to watch the interaction, and was struck by how determined the female seemed to avoid mating with this male. You’ll notice how the male is biting the female much lower down the body than is normal during mating, indicating how the female is trying to get away. Her dewlap is completely extended during this interaction.

The chase went on for several minutes before the female ran to the end of a thin branch and another male showed up to chase the first male away. I proceeded to catch and mark this second male, and later observations revealed him to be the resident territory holder of the tree.

A little later, we caught a male in the tree adjacent to one in which the showdown occurred. In a fantastic stroke of luck that anyone whose work depends on identifying individual animals in the field will appreciate, we were able to determine that this male from the adjacent tree was in fact the first of the two males observed earlier.

How, you ask, did we perform this forensic  wizardry? Observe the second tiny tail of the interloper attempting the forced copulation:

Caught red-handed!

I was showing these photos to Jonathan Losos the other day, and he immediately noted that the observation of a female using her dewlap was pretty rare. Of course, the obvious response was to write a blogpost about it, but then we realised that with Anole Annals‘ daily viewership of up to 1500, we could do more than just write a blogpost–we could do citizen science! So this, ladies and gentlemen, is an invitation to all of you to help build a  dataset. It’s more than the usual request for participation and comments that I end many posts with–it’s a challenge to all of us AA readers to keep an eye and camera out for examples of females using their dewlaps, so that we can together figure out a pretty basic piece of Anolis biology.

We’ve done this sort of citizen science before, quite successfully: here’s Kristin Winchell’s call for data on urban anoles, and here’s the resultant analysis.  And there’s all sorts of exciting natural history questions that would be impractical for individuals to tackle on their own, but that we can solve easily as a team. Let’s make this blog a citizen science hotspot!

Two days ago, the Boston Globe had an article online,

Winter storm causes havoc in US South

CTmax, Tb, and CTmin of cybotoid anoles & env. temperature. Modified from Fig 2 in Muñoz et al.

AA contributor Martha Muñoz’s work on altitudinal variation in the cybotoid anoles has already netted her the Raymond B. Huey award and of course, been featured on AA. A big chunk of this work, co-first authored with Maureen Stimola, has just been published by the Proceedings of the Royal Society B. If you haven’t read it yet, check it out.

I love this paper. However, in the spirit of full disclosure, I’m completely biased as I happen of be one of the co-authors. But I’m sure I’d love it anyway. Why? In part because it tests a clear hypothesis using multiple lines of evidence and eliminates confounding explanations – characteristics every paper should have. It also has cool (or should I say hot?) results. However, more than this, I think this paper demonstrates the power of combining good ole’ fashioned (yet cutting edge) field work with macroecological and macroevolutionary models, demonstrating how these different approaches can really complement each other.

What did Muñoz and company find? Briefly, they looked at hot and cold tolerance (CTmax and CTmin) of six species of cybotoid anoles on Hispaniola, in relation to elevation. They found far more variation in CTmin than CTmax across species (and populations). By bringing in a little macroecology, they showed that CTmax isn’t correlated with environmental temperature, but CTmin is, i.e. when the going gets cold, the anoles get colder – sort of. The catch is that while CTmin strongly tracks temperature, daytime body temperature does not. This is a neat result in and of itself and fits well with a big, recent, data-mining paper showing similar trends across hundreds of both ecto- and endothermic species. But while it doesn’t have the breadth of that paper, Muñoz et al. were able to go further. Firstly, bringing in a little macroevolutionary analysis, they showed that yes, CTmin has actually evolved significantly faster than CTmax. Neat, but at this point you should be asking yourself, “What about acclimatization?” and “Is this just plasticity?” Muñoz et al. asked the same thing and headed back to the field. A lot of work later and the answer was no. An acclimation experiment rejected this possibility.

At this stage, most macroecological and macroevolutionary analyses would have to stop at the identification of a clear, and intriguing pattern of fast past evolution of cold tolerance along an elevation gradient, but little CTmax evolution. The Discussion of such a paper would suggest potential hypotheses to explain the pattern and that would be that. But Muñoz et al. again went further and, by working in the field to measure perch use and operative temperatures, worked out why . The key result showed that lizards can behaviourally thermoregulate to escape the heat, thus reducing selection on heat tolerance, i.e. the Bogert effect. However, the nighttime cold cannot be escaped (actually, it can, by moving to England where it hasn’t dipped below -2 deg C this winter. Enjoy that polar vortex America!), leading to selection on cold tolerance.

Like I said, very cool results and a real testament to the power of using field experiments and macroevolutionary models to inform each other and go beyond what each approach could do in isolation. So please read it, challenge it, and build on it.