Category: New Research Page 42 of 66

Hello once again from the IBS in Miami. As I mentioned in my last post, anole presentations are a little thin on the ground here (though not around the conference centre where, with the help from some locals, we saw sagrei, carolinensis, equestris and distichus today).

I did have the opportunity yesterday to check out the the second of two anole presentations here – a new look at the sub-fossil lizard communities, with a focus on a question familiar to many readers of this blog: What’s the deal with A. pogus on Anguilla?

Has A. pogus ever been on Anguilla? Nope.

The study is being led by Melissa Kemp, from Liz Hadly’s lab at Stanford. Melissa has re-analyzed lizard dentaries from excavations on Anguilla that featured heavily in an anole character displacement versus taxon cycle debate in the early 90s.

By analyzing the size distribution of anole dentaries dating back 10,000 years on Anguilla, Melissa argues that not only is there a lack of evidence for a taxon-cycle involving A. pogus, but that there’s no evidence that A. pogus has occurred (in meaningful numbers) on the island at all! To further test this, Melissa has sequenced a portion of cytochrome b for five specimens thus far, all of which have turned out to be A. gingivinus, with more sequences coming down the pipeline.

Anoles aren’t the only lizards Melissa has uncovered – with Thecadactylus, Ameiva and Leiocephalus all present. Anoles have dominated the fauna in all but the earliest (and sparsely sampled) time slice and Leiocephalus was historically present (but probably not abundant) but disappeared several thousand of years ago and has not reappeared in the sub-fossil record since.

This was my first exposure to sub-fossil analysis of lizard communities and I was definitely impressed. I don’t have a sense of how much similar work there is in the literature (but I’m sure readers of the blog can educate me), but there seems substantial scope to collaborate with zoo-archaeologists to get more specimens and data on past trait variation and anole assemblage composition.

We’ve had a lot of hoohaw in these pages about amber Anolis, but anoles are not the only lizards represented in the Dominican amber fauna. In particular, a number of fine specimens of amber geckos are known from the D.R., as well as from amber deposits elsewhere. One such species is Sphaerodactylus dommeli. Embarrassing as it is to anole aficionados, this specimen has at times been suggested to be an anole, hard as it may seem to confuse such a lowly gecko with something as magnificent as an anole. In any case, Daza et al. have just published a magnificent analysis demonstrating that the specimen is, indeed, a gecko, and providing tips on how to avoid such unwholesome confusion in the future. Moreover, confirmation of the specimens identity will allow it to be used as a calibration point in future molecular studies of Sphaerodactylus phylogeny.

Anolis bicaorum from Utila, Bay Islands, Honduras. Photo by J. Losos.

Will global warming allow the blue-headed anole, A. allisoni, to move into the forest in the Bay Islands? This individual was photographed on Roatan by J. Losos.

Climate warming is a sad reality that environmentally defines our era. Over the next century, conservative estimates suggest that air temperatures will rise about 3° C. One imperative in research is to try to understand how reptiles, whose physiology is tightly linked to thermal environment, are going to be impacted by these increasing temperatures. During a symposium honoring Ray Huey, a leading biologist (and an anologist, to boot!), Michael Logan of Dartmouth College gave a talk on how small-scale estimates of thermal variation, rather than weather stations, yield interesting and perhaps counterintuitive results for how tropical lizards will be impacted by hotter temperatures. Predictions of potential impact to date rely heavily on temperature data gathered from weather stations – those provide a resolution of one square kilometer. For small reptiles, like tropical anoles, he argues that we need a finer resolution. To this end, Logan launched several operative temperature devices (sensors that perceive temperature as a lizard would, rather than just air temperature) on Cayo Mayor and Utila, which are islands in the Bay Island Archipelago in Honduras. We’ve discussed the anoles of the Bay Islands here on our blog before. On Cayo Mayor, Anolis lemurinus is found in the closed-canopy forest, while the blue-headed lizard,  A. allisoni is found in more open habitats. A close relative of A. lemurinus, Anolis bicaorum, is found throughout Utila. Because closed-canopy forests are more thermally homogenous (less variation in available temperatures due to less access to sun and shade patches), the expectation is that, under a scenario of climate warming, the open habitat species A. allisoni should be able to invade A. lemurinus‘ habitat. Logan says that A. allisoni will not invade the forest habitat, although the details of the analysis suggest to me that they might. From what I saw, increasing temperatures in the forest should allow A. allisoni to invade the newly available warm habitat. He does find that A. lemurinus should experience a loss in potential daily activity hours because of increasing temperatures, putting this species at risk. The common species (A. bicaorum) will actually experience more hours of activity and likely benefit, at least in the short term, from increased temperatures. Logan concludes that more micro-scale measurements provide the appropriate resolution for studies of thermal performance in lizards, and will be the wave of the future.

Aggressive encounter between anoles. Both opponents are watching each other with their right eyes. Photo: Johnson Lab, Trinity University

Have you ever gotten an angry look from an anole? Has he ever displayed at you, demanding that you get out of his territory? If so, chances are that if an anole was giving you the stink eye, he with using his left side! I’m blogging live from the Society for Integrative and Comparative Biology (SICB) meeting in San Francisco. My first stop has been to view Michael Patton’s poster examining the neuroanatomy of aggressive behavior. Patton is a senior undergraduate student at Trinity University working with Dr. Michele Johnson. Early birds at SICB have the opportunity to put their posters up for early viewing, so I got a sneak peek of his work last night although he’s not slated to present until Saturday.

For his project, Michael addressed the question of brain lateralization in aggressive displays. Some evidence suggests that anoles tend to favor their left side during competitive encounters. Patton and colleagues built on these studies by examining behavioral laterality in the field and neuroanatomy in the lab in the same individuals. Through observations of wild A. carolinensis, Patton found support for this idea – the winning male tended to view his opponent from his left side!

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Figure 1 from Campbell-Staton et al. 2012.

This past summer, two groups of authors published reports on the phylogeography of the only anole native to the continental United States: Anolis carolinensis. Each report sought to characterize genetic diversity across this species’ range by identifying genetically distinct populations, inferring historical demographic events, estimating the absolute timing of diversification events, and testing the hypothesized impact of riverine barriers and Pleistocene glaciation on geographic differentiation.

Because these two reports effectively appeared simultaneously (Tollis et al.’s report appeared on June 7th in PLoS ONE and Campbell-Staton et al.’s report was accepted for publication on June 18th at Ecology and Evolution), and do not cite or discuss one another’s work, I thought it would be worth writing a post that compares and contrasts their results and conclusions.  I’m going to focus in particular on three specific results reported by both groups of authors: (1) diagnosis of geographically and genetically distinct populations, (2) inference of historical demographic processes within populations, and (3) estimates for the timing of A. carolinensis diversification.  While the two studies largely agree on the first two results, they appear to disagree somewhat on third.

1. Diagnosis of geographically and genetically distinct populations

Sondra Vega, a graduate student at the University of Puerto Rico, writes:

A green anole eating a piece of fruit that fell from a bird feeder. Photo from http://4.bp.blogspot.com/_I_xaKqQzxyY/R4g96myXR_I/

In lizards, omnivory/frugivory is considered unusual and particular of some species; even though dietary studies indicate that many species add plant products to their diet.  In spite of the fact that seeds and fruits have been reported in stomach content or fecal pellets of Anolis, their importance and contribution to the diet of these lizards is still unknown. At present, the general consensus is to categorize Anolis as strict insectivores.  Therefore the extent by which omnivory/frugivory plays a role in the Anolis diet still needs to be assessed.

My research aims to determine how the variations in food abundance in two forests at the northern limestone region of Puerto Rico affect the degree of omnivory/frugivory and trophic position of Anolis lizards. I am using stable isotope technology to analyze the omnivory/frugivory and trophic position of the Anolis lizard as well to quantify the importance of fruits to the diet of the omnivorous Anolis species.  Stable isotopes are a novel technique that has the potential to elucidate diets, capture interactions such as trophic omnivory, and track energy or mass flow through ecological communities.   The information will help to better comprehend the functional role of Anolis lizards in the dynamic and structure of food webs and in ecosystem function, as well as the dynamics of vegetation in tropical forests.  Although this project is focused on anole lizard species of Puerto Rico, the findings are of relevance for understanding of islands where lizards are also a dominant component of ecosystems.

Ventral and dorsal view of polydactyl anole, click to enlarge.

As Rich Glor mentioned recently, we are in the second year of an experimental hybrid cross between two bark anole species.  Although we are still early in this year’s experiment, we have had about 50 eggs hatch and, surprisingly, two have had malformed forelimb digits. The first was missing two toes on one of its forelimbs and died a few days after hatching. The second (pictured above) hatched with six toes, but has been otherwise healthy. Each of these toes has an intact claw, and at least one has lamellae. The fourth digit (from closest to the body counting outwards) seems to lack the (expected) scansor and is permanently bent upwards.

Mats Olsson and colleagues (2004) found malformations in the limbs and jaws and kinked backbones in crosses between populations of Lacerta agilis. Of the over 800 hatchlings in last year’s F1 experiment, we found a few animals with malformed spines, but not a single animal with digit or jaw issues. It’s particularly interesting (to me at least) that these issues have manifested in the backcross generation, an issue I hope to investigate further as more animals hatch.

Polydactyly has been reported in captive-bred crested geckos (Correlophus ciliatus), but I couldn’t find anything about anoles. Has anyone else seen something similar in anoles? If so, please let us know in the comments.

Photos by Gabe Gartner and Kurt Schwenk.

This is a little far afield for anole aficionados, but recent years have seen a revolution in our picture of lizard (including snake) phylogeny. Traditionally, based on morphological analysis, lizards were thought to split into two groups, the iguanians (including anoles, other iguanids, agamids, and chameleons) and scleroglossans (everything else, including snakes). However, starting with a paper by Townsend et al. in 2004, a different picture emerged in which iguanians were nested high in lizard phylogeny, closely related to anguimorphs (such as alligator lizards, gila monsters, and monitors) and snakes. A series of subsequent studies came to essentially the same conclusion, most recently the output of the “Deep Scaly” NSF Tree of Life project which sequenced DNA from 44 genes.

Two views of lizard phylogeny. From Losos et al. (2012)

I think that most of the field had come to accept that the molecular tree was correct. But along comes a paper by the morphology team of Deep Scaly, a remarkable analysis in which 194 species were all micro-CT scanned and examined in others ways, leading to a data set of more than 600 morphological characters, 247 never previously used in phylogenetic studies. Analyzed with state-of-the-art methods, the results resoundingly support the original morphological tree and give absolutely no morphological support for the new molecular tree. The authors do an excellent job in not being strident in insisting that the morphological tree is correct, but just highlighting how very unusual morphological evolution must have been if the molecular tree is correct. Moreover, the authors note that based on analyses including the molecular data, the “Archaeopteryx” of squamates, Huehuecuetzpalli mixtecus, is placed high in the phylogeny, rather than in the basal position where morphology has long placed it. If, indeed, the molecules are right, what does that say about our ability to ever reliably place fossil species in a phylogeny?

Either the morphological or the molecular tree is incorrect, and either molecular or morphological data have been evolving in a way for which there is no good explanation. This is truly a conundrum, which was the point of a perspective piece just published by David Hillis, Harry Greene, and me. We don’t have any answers, but thought it was an interesting enough question worthy of further attention.

Earlier this year, we mentioned a paper by Juli Wade reviewing research on the green anole, which has become a model organism for integrative studies of reproductive behavior in vertebrates. One example of such research is a paper recently published in her laboratory by Cohen and Wade in which levels of testosterone were experimentally manipulated to see the effect of this hormone on gene expression in different regions of the brain. The abstract gives the details better than I could:

“Aromatase and 5alpha-reductase (5-alpha-R) catalyze the synthesis of testosterone (T) metabolites: estradiol and 5-alpha-dihydrotestosterone, respectively. These enzymes are important in controlling sexual behaviors in male and female vertebrates. To investigate factors contributing to their regulation in reptiles, male and female green anole lizards were gonadectomized during the breeding and non-breeding seasons and treated with a T-filled or blank capsule. In situ hybridization was used to examine main effects of and interactions among sex, season, and T on expression of aromatase and one isozyme of 5-alpha-R (5-alpha-R2) in three brain regions that control reproductive behaviors: the preoptic area, ventromedial nucleus of the amygdala and ventromedial hypothalamus (VMH). Patterns of mRNA generally paralleled previous evaluations of intact animals. Although no main effects of T were detected, interactions were present in the VMH. Specifically, the density of 5-alpha-R2 expressing cells was greater in T-treated than control females in this region, regardless of season. Among breeding males, blank-treated males had a denser population of 5-alpha-R2 positive cells than T-treated males. Overall, T appears to have less of a role in the regulation of these enzymes than in other vertebrate groups, which is consistent with the primary role of T (rather than its metabolites) in regulation of reproductive behaviors in lizards. However, further investigation of protein and enzyme activity levels are needed before specific conclusions can be drawn.”

Here at the Glor Lab we’re in the second year of a major anole breeding experiment.  Specifically, PhD student Anthony Geneva is completing the second generation of an experimental study of reproductive isolation that was the subject of his poster at the Evolution meetings this past summer (see this previous post on Anole Annals for more on this poster).  I’m happy to report that egg production thus far has been steady and that the we’ve had hatchling emerging for a few weeks now.  In the photo above, you can see a baby just emerging from an egg in the foreground and other eggs individually incubating in vermiculite in the background.  We’ll have more to report on this experiment in the coming weeks.  We’re particularly interested in sharing information on how we’ve encouraged breeding this year by manipulating light and humidity, and in learning how others might have tried to do the same.