Anole Annals

A male Anolis cristatellus dewlaps on a tree in Miami, Florida. Picture reproduced with permission from Kolbe et al. (2012).

Anoles are remarkably adaptable creatures. You can find anoles in hostile environments, such as the tops of mountains in the Dominican Republic, in near-desert environments, and in places with over-winter freezing. Anoles are also a model system for rapid evolution; in response to strong selective pressure, an equally strong evolutionary response occurs within a few generations. It is perhaps unsurprising, then, that anoles are also one of the most invasive reptiles in the World. Although they are endemic to the tropical and subtropical regions of the New World, today anoles can also be found in such remote places as Guam, Hawaii, Taiwan, and Hong Kong.

One of the major questions surrounding anole invasions is how the organisms will respond to the challenges of a new environment. When anoles invade new environments they inevitably encounter new thermal and hydric conditions – how do these anoles adapt to a different environment? Jason Kolbe has spent many years exploring the ecology and genetics of Anolis invasions, and has focused especially on invasions in Florida (1, 2, 3). The Puerto Rican trunk-ground, A. cristatellus, has been found in Key Biscayne and South Miami since the mid-1970s. Ambient temperature is important for A. cristatellus and other anoles have been documented to acclimate to low temperatures. In this study Jason Kolbe and colleagues addressed two questions: (1) To what extent does the thermal environment change from Puerto Rico to Florida? and (2) Is there a phenotypic response in tolerance to cold?

Read More

Laura Rubio-Rocha, a masters student at UT Knoxville, presented an anole double-header at Saturday evening’s poster session.  In one poster, Laura presented work on thermal physiology of two anole species that occur in the United States: the native green anole (A. carolinensis) and the introduced brown anole (A. sagrei).  By sampling each species from a number of localities across a latitudinal transect extending from southern Florida to southern Georgia, Laura was able to test whether populations or species vary in their ability to tolerate cold temperatures.  To evaluate each species’ ability to tolerate cold temperatures, she used a simple behavioral assay that diagnosed the lower critical thermal minimum (CTmin) as the temperature at which a species no longer responded to physical stimuli.  Although anoles readily recover from this state in captivity, anoles in field aren’t likely to last long when incapacitated.

When CTMin was assessed in the field, Laura found that thermal tolerance largely mirrored the latitude of sampled populations.  Within each species, those that occurred further north were better able to cope with lower temperatures than population sampled further south.  A strong difference between the two species, with green anoles (A. carolinensis) being able to tolerate much colder temperatures than brown anoles (A. sagrei).  The story, however, doesn’t end here.

Recognizing that some degree of variation in a given individual’s cold tolerance might result from acclimation and plasticity, Laura conducted her analyses both in the field immediately after capture and after allowing the animals to acclimate to the conditions of a common garden laboratory environment for several months.  When Laura analyzed her laboratory data, she found that the strong difference in cold tolerance between species persisted, but the differences within populations of each species from localities across a latitudinal gradient were no longer evident.  Her results suggest that some degree of cold tolerance is genetically determined, but that variation within species along a latitudinal gradient is likely a plastic response.

A terrible photograph of Blair Hedges’ presentation (sorry, I was stuck in the back of the room).

Blair Hedges used his talk at WCH7 to present his exciting new results with Caribbean skinks.  You can read more about this work in the paper he published in Zootaxa earlier this year with Caitlin Conn (pdf link from Hedges webpage) and in Jonathan’s previous AA post on this paper. Using analyses of a dataset that includes four genes (three mitochondrial and one nuclear) from 136 individuals representing 14 of 16 genera, Hedges and Conn report discovery of dozens of previously unrecognized species and advocate recognition of 16 genera of skinks across the new world.  Unfortunately, many of the new species identified by Hedges and Conn seem to already be extinct, and Hedges showed some very compelling data to support the hypothesis that the decline of skink populations was a response to the arrival of the mongoose.

Sondra Vega reported the results of a fascinating study of diet in nine Puerto Rican anoles. Using isotope analysis from tail tissue, she concluded that all species are to some degree omnivorous, not terribly surprising in some sense because a number of species have already been reported to eat fruits and berries. What is surprising is that there seem to be two discrete groups, suggesting that some species are more omnivorous than others. In particular, some are more carnivorous (cooki, monensis, pulchellus, and stratulus) and others more omnivorous (cristatellus, cuvieri, evermanni, gundlachi and krugi).

Luke Mahler reported the amazing news (truth in advertising: I’m a co-author) that a large and very distinctive new anole has been discovered in the Dominican Republic. Here’s the abstract:

Discovery of a short-limbed giant Anolis from Hispaniola supports a deterministic model of island evolution and community assembly

We report the discovery of a species of giant anole from Hispaniola that provides new evidence for determinism in the evolution and assembly of Caribbean island Anolis faunas. The new species is most closely related to Hispaniolan ―crown-giant‖ ecomorph anoles (Anolis ricordii clade). However, it is ecomorphologically most similar to Cuban giant twig anoles of the Chamaeleolis clade: both are very large anoles with short limbs and a short tail that tend to utilize relatively narrow perches in cluttered habitats this discovery adds a new dimension to the phenomenon of among-island ecomorph matching that characterizes Greater Antillean anole faunas. In addition, phylogenetic comparative analyses suggest that key aspects of the similarity of Hispaniolan and Cuban giant twig anoles may be the product of evolutionary convergence. Being restricted to a narrow band of threatened mid-elevation forest near the border of the Dominican Republic and Haiti, this new species should be considered critically endangered.

Kat Wollenberg presented a very interesting analysis of geographic variation in Hispaniolan  A. cybotes, distinguishing effects due to environmental differences, microhabitat use, and genetic relatedness. One particularly novel approach was to compare elevational differences that occur independently in a number of different mountain ranges (the different mountain ranges are the red parts in Hispaniola above).

Here’s the abstract:

Diversification within adaptive radiations: the case of Hispaniolan trunk-ground anoles

The evolutionary processes that produce adaptive radiations are still enigmatic to date, as these are by definition recognized after the radiation has occurred, which makes it difficult to study them as an ongoing process. One way to connect pattern to process is to study the processes driving divergence today among populations of species that belong to an adaptive radiation, and compare the results to patterns observed on deeper level. In this paper, we tested whether evolution is a deterministic process with equal outcomes during different stages of the adaptive radiation of Anolis lizards. On the example of a clade of trunk-ground anoles, we inferred the adaptive basis of spatial variation among contemporary populations, and tested whether axes of phenotypic differentiation among them mirror known axes of diversification at deeper levels of the radiation. Although non-parallel change associated with genetic divergence explains the vast majority of geographic variation, we found phenotypic variation to be adaptive as confirmed by spatial convergence across the landscape, as well as genetically independent habitat-associated morphological variation. Morphological diversification of populations occurs recurrently along both tested axes of diversification previously identified in the anole radiation, but different sets of characters are affected.

Ray Huey and Luisa Otero in front of their poster

Anole Annals has previously had a number of posts on the exciting ongoing project in Puerto Rico examining climate change and thermal biology of anoles. Last night, Luisa Otero presented the results of one aspect of the project, examining the reproductive biology of Anolis cristatellus in a forest and an adjacent (i.e., across the street) open habitat. Previous work by Ray Huey (specifically, his dissertation research in the 1970s) showed that in the open in lowland Puerto Rico, crested anoles are able to thermoregulate and maintain a high and constant body temperature, but in the forest, where good sunspots are scarce, anoles don’t thermoregulate and have lower temperatures.

Luisa’s work confirmed that this pattern has not changed even as Puerto Rico has warmed in recent years–open habitats are still thermally preferable for crested anoles. The exciting new twist is that Luisa examined the reproductive rate of the lizards. Every month of the year, more female anoles are gravid in the open habitat, but this result is particularly striking in the winter, when reproduction slows down in the open, but seems to cease entirely in the forest. Hence, differences in thermal biology do appear to have strong effects on individual fitness and presumably population dynamics, and, at least for now, global warming has not changed the relative suitability of different habitats.