Category: New Research Page 44 of 66

Brown anole eating a curly tail lizard. Photo by Joseph Wasilewski.

We’ve had a number of posts concerning predation by curly tail lizards on brown anoles, in the Bahamas, Florida, Cuba and elsewhere. Now comes a report from near Miami that the brownies aren’t just sitting back and taking it. Rather, they’re rounding up vigilante posses to track down and consume baby curlies, hitting the predator’s population where it’s vulnerable. Ok, perhaps that’s a stretch, but in a recent note in Herpetological Review, Krysko and Wasilewski publish the first report of Anolis sagrei preying on Leiocephalus carinatus, revealing that the ecological interactions between the two species are more complicated than previously thought: we already knew that curlies prey on brown anoles and that the two species also compete for some of the same insect prey (making this an example of the phenomenon of intra-guild predation),  but this study raises the possibility that the interaction–and its likely ecological and evolutionary consequences–could be substantially more complicated. One might think that because of the massive size advantage of the curly-tails, the effects must mostly be one-way; however, the massive population size differential between the two species means that brown anoles, in theory, could greatly affect curly tail populations as well. Although the effects of curly tails on brown anoles have been studied, the opposite experiment has not been done. Of course, previous work on tiny Bahamian islands indicates that curly tails substantially reduce brown anole populations, but maybe dynamics are different in larger and more complicated ecosystems. Personally, I wouldn’t bet on it, but who knows?

Battling green anoles. Photo from http://dmcleish.com/Maui2009/AnoleFight/DSC_0278.jpg

Both theory and empirical examples from many types of organisms indicate that animals alter their fighting behavior based on the outcome of previous fights. That is, if an animal won its previous fight, it is likely to win its next one, whereas previous losers are likely to keep on losing. In a new paper in Ethology, Garcia et al. examine whether such winner and loser effects occur in the green anole, A. carolinensis.

To create winners and losers independent of their innate fighting ability, the investigators first staged encounters in which one lizard was 40% larger than the other. Because size is a very good predictor of encounter outcome, they used this method to create animals which had won or lost their first encounter. Indeed, most of the larger animals won in these matches. Then, in the second round, they placed individuals of the same size together, one of which had won its previous encounter and the other that had lost.

Results did not support the hypothesis: probability of winning was not affected by previous experience: winners in the first round were no more likely to triumph in the second round than were first round losers. However, there was one interesting finding: losers that had put up a good fight in Round 1 were likely to win Round 2, whereas those who hadn’t continued to lose. Two possible explanations are either: 1) that the feisty losers were intrinsically more aggressive and couldn’t overcome the size disadvantage in Round 1, but when paired against similar-sized animals, were able to use their aggressiveness to overpower their opponent; or, second, that this is an example of a variation of the “loser effect,” only that it is not the outcome of the fight, but the quality of it, that matters. Losers who put up a good fight might still feel emboldened and thus do well in the future, whereas losers that lose badly may continue to lose in the future.
Mark J. Garcia, Laura Paiva, Michelle Lennox, Boopathy Sivaraman, Stephanie C. Wong, & Ryan L. Earley (2012). Assessment Strategies and the Effects of Fighting Experience on Future Contest Performance in the Green Anole (Anolis carolinensis) Ethology, 118, 821-834 DOI: 10.1111/j.1439-0310.2012.02072.x

It’s been a good couple of years for studying lizard smarts. Last year, Manuel Leal demonstrated keen cognitive abilities in Anolis evermanni. More recently a couple of studies Down Under have shown that slippery Aussie skinks have a lot going on upstairs as well. Over at The Lizard Lab, Martin Whiting has just posted a nice review of these studies.

For those who work primarily in the West Indies, it can be difficult to imagine a lizard fauna dominated by anything other than anoles.  However, if you’re interested in learning more about lizard communities that don’t include anoles, no book fits the bill better than L. Lee Grismer’s recent monograph on the Lizards of Peninsular Malaysia, Singapore and their Adjacent Archipelagos.  Grismer takes readers on a tour of Peninsular Malaysia’s impressive lizard diversity, with species-by-species accounts that include morphological diagnoses, notes on coloration in life and among sexes, dot maps, and detailed notes on each species’ natural history.  Grismer is the first to comprehensively review Peninsular Malaysia’s 128 lizard species, and his book represents the “first time the entire distribution of this fauna has been precisely mapped.”  Of course, Grismer’s book is also chalk full of spectacular photographs, including many of Grismer’s trademark photos of animals in their natural habitat.

Map from Malaysian Bat Education Adventure: http://www.ttu-mbea.org/krau-wildlife-reserve/

Sandwiched between Thailand and Myanmar to the north and Indonesia to the south, Peninsular Malaysia is a geographically, historically, and ecological diverse region that includes numerous mountain ranges, offshore archipelagos, and isolated karstic rock outcrops.  The habitats of Peninsular Malaysia range from mangrove forest to lush multi-layered Dipterocarp forest to “post-apocalyptic” oil palm plantation dominated landscapes.  Grismer does a great job familiarizing readers with the region by beginning his monograph with detailed information of the region’s biogeography and environmental diversity.

Most importantly, of course, Peninsula Malaysia is home to 128 lizard species, mostly geckos, skinks, or agamids, but also the occasional dipamid, lacertid, varanid, and leiolepid.    Some 45% of these species are endemics, the vast majority of which are skinks and geckos that are narrowly distributed in montane habitats, isolated karstic rock outcrops, or off-shore archipelagos.  The agamids, however, are likely to attract the immediate attention of anole lovers because this group includes most of the region’s arboreal, diurnal, and often conspicuous, lizards.

Image from http://animals.nationalgeographic.com/animals/reptiles/draco-lizard/

The most diverse agamid radiation in Peninsula Malaysia is Draco, the remarkable genus of gliding lizards that is found throughout much of southeast Asia.

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Variation in the back patterns of Anolis sagrei in the Bahamas. From Calsbeek and Cox (2010).

Last year, we had a series of posts discussing the evolution of dorsal patterns of female anoles, as well as several studies that reported intrapopulation variation in female patterning. Why such variation should exist is a mystery, and studies on both A. humilis in Costa Rica and A. sagrei in the Bahamas failed to find evidence that natural selection was acting on this variation.

Now, Calsbeek and Cox report an experimental study of natural selection on dorsal pattern on small islands in the Bahamas. They introduced anoles with the three patterns shown on the left onto four small islands. Two of the islands had birds and snakes, the other two had neither. One predator-exclusion island was studied in 2008, the other three in 2009. In addition, the authors measured selection in a natural population over the course of four years.

The major result of the study is that not only was survival reduced on islands with predators, but also in the presence–but not absence–of predators, the intermediate diamond-bar pattern had higher survival than the other two patterns. How this intermediate pattern leads to heightened survival is not clear, and the authors propose a few hypotheses for future testing.

R. CALSBEEK & R.M. COX (2012). An experimental test of the role of predators in the maintenance of a genetically based polymorphism Journal of Evolutionary Biology DOI: 10.1111/j.1420-9101.2012.02589.x

In my three previous posts [1,2,3], I have discussed Nicholson et al.’s ecomode concept and their conclusion from it that the ecomorph concept should be rejected. Here I conclude my discussion by addressing two other related points raised in Nicholson et al., whether differences in forest structure are responsible for different evolutionary patterns in the islands and on the mainland, and their critique of my 1992 paper on the sequence of ecomorph evolution.

Are Differences in Forest Structure Responsible for Different Evolutionary Patterns in Mainland and Island Anoles?

Nicholson et al. state (pp. 54-55): “In discussing differences between island and mainland anoles, Losos (2009) considered, but dismissed, forest structure as a driving factor in shaping anole assemblages, suggesting that, to anoles, a tree is a tree…[W]e are impressed with the complex nature of the moist, wet, and rain forests of Central and South America (Solé et al. 2005) that are home to the majority of anole species. The heavily fluted bark of Neotropical rainforest canopy trees such as Lecythis must require substantially different limb and toe pad shapes in anoles that use these trees than those that use the smooth bark of canopy trees such as Pterocarpus. The facts that bark texture is likely to be much more diverse in mainland than island forests, and that trees with appropriate bark texture are likely to be so much more widely dispersed in mainland than island forests, must play an important role in making morphology of mainland anoles so much less predictable than it is for island anoles. The fact that island forests are dominated by a relatively few short, smooth-barked tree species must limit the number of morphs that anoles can attain, must increase the density that anole populations can maintain, and must increase the interactions among sympatric species above that experienced by mainland anoles. Additionally, the differences in the structure of understory shrubs associated with mainland areas possessing an ancestral fauna that includes grazing mammals, compared to island areas that lacked such grazers (Dirzo and Miranda, 1990), must affect habitat available for adaptive radiation in anoles. In short, we see little evidence that the assembly rules proposed for anole communities on Caribbean islands will ever be discovered as applicable to mainland anoles, because the factors shaping vegetation structure are so different between island and mainland forests.”

And by the end of the paper (p.68), the idea has been transformed into a firm conclusion: “We note that evolution of ecomodes appears to be widely constrained within anoles and does not necessarily lead to constrained morphology within an ecomode because variation in forest structure across the geographic range of anoles is so great.”

It is certainly plausible that differences in vegetation structure between mainland and island forests are responsible for different patterns of ecomorphological evolution in the two regions. But what is the evidence for this? I have actually looked for comparisons of structure between mainland and island forests and have not found any relevant literature. The authors only cite two papers and neither documents differences between mainland and island forests: Solé et al. (2005) is about differences between canopy and understory at Barro Colorado Island, and Dirzo et al. (1990) is a comparison of mainland sites with and without large mammal herbivores (note: these references were presented by Nicholson et al. to document appropriate points about mainland forests; I am not claiming they were inappropriate citations, only that application to Caribbean forests is entirely an extrapolation of the authors). The authors may well be correct that mainland and island forests differ, but they do not provide any evidence to support this claim. Moreover, even to the extent that mainland and island forests do differ in structure, the effect such differences have had on anole evolution is entirely conjectural (e.g., perhaps different bark texture would select for differences in toepad structure, but to date, there are no data relevant to such a claim).

Indeed, one may question how likely it is that differences in tree structure actually affect anole morphological adaptation.

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After presenting the concept of “ecomodes” (equivalent to habitat specialist types) as an alternative to “ecomorphs,” Nicholson et al. argue that the ecomorph concept should be abandoned. My previous two posts have discussed the ecomode idea and what it can tell us about the evolution of habitat use in anoles (1,2). In this post, I analyze their chain of reasoning that leads to the call to discard ecomorphs.

The argumentation in Nicholson et al. undergoes a curious transformation. At the outset they note, rightly enough, that a number of workers have found that the ecomorph concept developed for Greater Antillean anoles does not apply to mainland species, but by the end of the paper, they conclude that the ecomorph concept is fatally flawed and must be discarded in its entirety. How do they make this leap?

Let’s start by defining what we mean by “ecomorph.” In his classic 1972 paper, Ernest Williams defined an ecomorph as “species with the same structural habitat/niche, similar in morphology and behavior, but not necessarily close phyletically.” This definition has been quoted repeatedly and is the essence of how the term has been used throughout the literature on ecomorphs and their evolution. Thus, the trunk-crown ecomorph is composed of those species that are similar in morphology, habitat use, and behavior; moreover, to constitute an ecomorph, a set of species must come from multiple lineages, instead of composing a single clade. (It’s worth noting that the term “ecomorph” was coined by Williams in reference to anoles and has since been widely applied to other taxa, as discussed in a previous post).

Now, let’s trace the Nicholson et al. argument:

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One of the most significant potential impacts of Nicholson et al.’s proposed classification for anoles is that it would lead to changes in the binomials applied to most anole species.  For example, Anolis cristatellus would now be Ctenonotus cristatellus and Anolis chlorocyanus would now be Deiroptyx chlorocyanus.  The fact that Nicholson et al.’s classification would change so many binomials is the main reason we’re debating their proposed revisions; because binomials are the names that are most widely-used in the literature, changes to binomials are intrinsically more significant than many other types of taxonomic revisions.  The plusses and minuses of dividing anoles among multiple genera are discussed in numerous other recent posts on Anole Annals.  This post has a somewhat different goal – namely, to explain some of the proposed binomial changes proposed in Nicholson et al.’s classification that do not involve simply swapping one generic epithet for another.

In addition to simply dividing anole species previously recognized as Anolis among a number of new genera, Nicholson et al. introduce at least 48 new binomials that involve changes in the spelling of specific or generic epithets.  My purpose is to summarize and explain these changes to the best of my abilities.  As you will see, I soon reach the limits of my knowledge of both The Code and Latin and would like to ask readers more knowledgeable readers for enlightenment.

Understanding the majority of the name changes proposed by Nicholson et al. is relatively easy, as long as you take a moment to learn a bit about one of The Code’s article’s pertaining to Latin grammar.  Indeed, Nicholson et al. are compelled to change 35 species epithets due to a controversial provision of The Code that necessitates a match between the Latin genders of generic and specific epithets.  Most of the changes necessitated by this article of the code in Nicholson et al.’s proposed revision result from moving species from a masculine genus (Anolis) to a feminine genus (Audantia, Dactyloa, and Deiroptyx), and involve changing a trailing “us” to an “a” (e.g., Anolis chlorocyanus to Deiroptyx chlorocyana). A complete list of the species epithets that are being changed to match the Latin genders of their new generic epithets is included at the bottom of this post.

While most of the changes to specific epithets are due to the Latin gender issue, other changes have different explanations.  In some cases, the reasons for these other changes are well-justified.  Anolis etheridgei, for example, is changed to Deiroptyx darlingtoni because moving this species to Deiroptyx permits use of this species’ original specific epithet that was not previously permitted because it was the same as another species of Anolis (The Code does not permit two species named Anolis darlingtoni).

Nicholson et al.’s reasons for changing the fifteen remaining generic or specific epithets are less clear (at least to someone like me with no knowledge of Latin).  From the table below comparing the species epithets in Nicholson et al. to those in the Reptile Database, one generalization one might make is that most of the proposed changes involve vowels.  Some specific types of changes are applied more than once (e.g., a “u” is changed to an “i” in the names of both pumilus/pumilis and nubilus/nubilis) but other changes are unique (changing an “o” to an “io” in anfiloquioi/anfilioquioi).  I’ve checked the spellings in all of the original species descriptions that I have on hand and found that they tend to match the species names in the reptile database.  I believe the names in the original species descriptions are what The Code characterizes as the “correct original spelling.”  Based on my crude understanding of The Code, I have the impression that these “correct original spellings” cannot be changed to correct spelling or other grammatical errors that the author may have made either intentionally or unintentionally (only those changes that were not the authors fault, such as type-setting or printing errors can be corrected subsequently).  In one case the change might be  permissible because it involves an error in the original related to number of people being honored.  In one case, an “ii” is changed to an “i” seemingly against the letter of the code.  When I asked Nicholson about these changes, she told me that they were all made in accord with “the rules of Latin usage combined with ICZN rules for how you apply name changes.”

Can others out there assist me in interpreting the justification for these proposed name changes?

NOTE: I’m reluctant to even suggest the possibility that some new binomials are the result of typos, but this possibility must be considered in a few cases.  Nicholson et al. refer to A. macilentus (Garrido and Hedges 1992) throughout their manuscript, but refer t0 this species as A. maclientus in Appendix IV.   The fossil anole from Dominican amber is mentioned only a single time in the body of the paper, where it is referred to as domincanus rather than dominicanus (de Queiroz et al. 1998).  Similarly, a new genus name – Norpos – appears in Appendix III and again in Appendix IV when referring to the species parvicirculatus.  Tables of the changes to binomial names in Nicholson et al. are below the fold.

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Although we’ve been focusing a lot of attention on Nicholson et al.’s new classification for anoles, Daniel Scantlebury recently called attention to the fact that this monograph also contains “a bold hypothesis of the biogeographic history of” anoles.  I’m going to focus here on only one aspect of Nicholson et al.’s biogeographic analyses – namely, their use of two remarkable amber fossils to calibrate a Bayesian relaxed clock analysis supporting the hypothesis that anole diversification dates back to the Cretaceous.

Nicholson et al.’s hypothesis that anoles first appeared more than 90 million years ago and that most major clades of anoles originated prior to 70 mybp is likely to be one of the most controversial aspects their hypothesized biogeographic scenario.  These extremely old ages are significant because they make anole diversification compatible with a scenario that has long attracted the attention of vicariance biogeographers (Rosen 1975, Savage 1982, Crother and Guyer 1996).  Under this scenario, anoles occupied an ancient volcanic arc that originated in the Pacific ~120 mybp and formed a landbridge between North and South America in the Late Cretaceous (75-70 mybp) before moving on to form the present day West Indian islands.

I have characterized the ages for anole diversification in Nicholson et al.’s biogeographic reconstruction as “controversial” and “extremely old” because they are older than the age estimates obtained by most other studies.  Hedges et al. (1992) were among the first to use molecular methods to estimate ages for terrestrial vertebrate fauna of the West Indies, and reported ages for anoles and other taxa that were far too young to be compatible with Cretaceous vicariant events and the hypothesized Greater Antillean Landbridge between North and South America.  Hedges et al. (1992) suggested instead that anoles arrived in the West Indies via over-water dispersal.  Although Crother and Guyer (1996) criticized Hedges et al.’s use of immunological data and their resulting conclusions about over-water dispersal, more recent work has tended to support Hedges et al.’s conclusions by recovering ages for anoles and other terrestrial West Indian vertebrates that are too young to be compatible with the vicariant scenario hypothesized by Savage (1982), Crother and Guyer (1996) and Nicholson et al. (2012).

Daza et al.’s (2012) cladistic analysis of fossil data, for example, includes an update of the time calibrated tree generated by Conrad (2008) from available fossil material; this tree suggests that the Polychrotidae (the possibly non-monophyletic clade that includes anoles and other putative relatives like Polychrus) split from the Hoplocercidae sometime in the Eocene (~50 mybp).   Townsend et al.’s (2011) analysis of a multi-locus molecular phylogenetic dataset for iguanian lizards that used a BEAST analysis with 18 fossil calibrations suggests a split between Anolis carolinensis and the Corytophanidae at 50-70 mybp.  Most recently, Mulcahy et al.’s (In press) analysis of a multi-locus phylogenetic dataset for squamates in BEAST that relies on 14 fossil calibrations suggests that Anolis carolinensis split from Enyalioides laticeps 25-75 mybp (penalized likelihood analyses conducted by Mucahy et al. suggest a considerably older split between these two species that dates to around 80 mybp).

Recently published trees with estimates for the age of Anolis from Daza et al. 2012, Townsend et al. 2011, and Mulcahy et al. in press.

Why is there a discrepancy between the ages for anoles reported by Nicholson et al. and other studies?  

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