There is much variation in the form and function of vertebrate hearts. At one extreme sits the two-chambered, flow-through hearts of fish while at the other end sits the highly efficient four-chambered hearts of birds and mammals that create the complete separation of pulmonary (lung) and circulatory (systemic) systems. Understanding the relationships between heart performance and animal physiology has long fascinated biologists. But more recently, new lines of investigation have also began dissecting the developmental origins of cardiac variation to better understand the ways in which this critical organ has evolved. Several recent research papers have used lizards and snakes – most importantly, anoles – as their centerpiece in the hope of finding new clues about heart evolution and the origin of the fully divided ventricle. These studies fill an important gap in our knowledge of comparative heart development. Prior to this research the study of squamate heart development had lagged well behind species from other vertebrate lineages, sitting idly for over 100 years.
Author: Thomas Sanger Page 4 of 6
Thom Sanger is an Assistant Professor at Loyola University in Chicago. His lab specializes on understanding the developmental bases of Anolis lizard diversity.
Males and females of many species vary in their morphology, behavior, and physiology. Whether exaggerated weapons, elaborate coloration patterns, or dramatic differences in size, these sexual dimorphisms form some of the most eye-catching elements of biological diversity. These striking differences are often considered as a product of sexual selection, whether due to direct female choice for an elaborate structure or traits used by combative males to assert dominance. But additional patterns of dimorphism become visible with quantitative comparisons of male and female body proportions, which may yield additional clues to ecological differences between the sexes. Considering that patterns of sexual dimorphism can diverge rapidly among species it is no surprise that they have intrigued biologists since before Darwin.
Anolis brunneus from Crooked Island, Bahamas. A member of the carolinensis clade of anoles exhibiting extreme levels of facial length dimorphism.The male is the large lizard to the bottom left, the female to the upper right.
Earlier this year Jonathan Losos posted about a decorative anole figurine. I was lucky enough to receive one of these priceless collector’s items as a holiday gift. Because I am thoroughly amused by the story of Anna the Anole I thought that I would share her story here.
Doctor Anole, Mt. Lemmon, AZ
Among biologists one of the greatest honors is having a species named after them. Among climbers one of the greatest honors is inspiring the name of a new climb. (In fact, much like biology, local ethics and traditions often govern route nomenclature.) It turns out that I have scarred my research has inspired an old friend to name a new route with reference of our favorite scaly beasts. Here I present you, “Doctor Anole” at the Lizard Boulders, Mt. Lemmon, AZ.
Because climbing can, to some, seem a bit esoteric let me take a moment to explain the photo. Unlike climbing mountains or large cliffs, “bouldering” is a form of climbing where a person attempts to climb for only a few moves, but where each move may be at the absolute limit of their ability. Bouldering can just be a single move or, to the most brave, reach death defying heights while rope-free. On Doctor Anole the goal is to climb to the top of this boulder using the small seam for handholds. A pad is also placed below the climb to cushion a potential fall. Hopefully the moderate grade of V2 does not directly reflect my friend’s opinion of my climbing abilities or research.
Nicholson et al. recently undertook the bold mission of revising the taxonomy of our well-loved lizard genus, Anolis, based on the phylogenetic relationships among its many species. Not surprisingly this has struck a nerve with much of the anole community spawning a range of reactions immediately following its publication, some applauding their efforts but many expressing their concerns about the proposed change. If one of the author’s objectives was the generate discussion on this topic its clear that they have succeeded.
The Nicholson team should first be commended for their efforts to synthesize the historical literature on anole taxonomy, encompassing “387 recognized species and 112 additional nominal subspecies” with some reports dating as far back as the mid-1600s. This survey will likely serve as a benchmark for later systematic evaluations of this genus. However, the implications for their proposed revision extend well beyond the nuances of taxonomic rule or the analytical methods used to build phylogeny*. The issues arising extend into other biological disciplines and potentially undermine the rich intellectual history of anoles.
I, like many others, am a consumer of taxonomy and systematics. These are critical to the comparative analyses I perform and in communicating my findings to others in the anole community, herpetologists more generally, and other biologists more broadly still. Anolis has been a model for comparative biology for decades but is gaining increased attention by genomicists, neuroendocrinologists, and developmental biologists. Just this year, in fact, the anole community developed a system with which to share comparative molecular resources. Deconstructing Anolis into eight distinct genera could drive an intellectual wedge between the previously published literature and future studies, potentially derailing the continuity of information that is critical for academic advancement. This change could lead to unforeseen consequences that damage the broad utility of Anolis among biological disciplines that depend on the stability of anole nomenclature.
Nicholson et al. state, “the role of systematics is to advance our understanding of biological diversity.” While I agree with this statement in principle I feel that it is also important to ask if the benefits of revising this diverse taxon outweigh the risks I outlined above. The glaring disconnect between phylogenetic systematics and Linnean ranks is discussed at great length elsewhere and will be strategically avoided here. It is worth asking, however, whether the addition of new genera (specifically genera, not simply clade names) add anything new to our biological understanding of this group. Ultimately, can we more accurately communicate our findings using the revised nomenclature? While Nicholson et al. use monophyletic clades to distinguish the proposed genera – a well respected practice – the precise breaks are biologically arbitrary. In my opinion the suggested genera do not offer greater clarity to the natural history of this clade as they do not partition Anolis based on distinct biogeographic groups, groups with distinct ecologies, or groups with distinct, readily recognizable morphological features. In this proposed taxonomic scheme the ecological and morphological convergence of Anolis ecomorphs** that is widely discussed and cited throughout ecological and evolutionary literature becomes a confusing hodgepodge of convergent lineages from different genera. In my opinion it is overwhelmingly clear that the benefits of re-classifying Anolis lizards do not outweigh the ensuing upheaval of our research community.
At face value it appears that the overall motivation for revising Anolis is its diversity, as it is undoubtedly one of the most diverse tetrapod genera. However Anolis pales in comparison to many invertebrate genera. The beetle genus Agrilus (jewel beetles) has an estimated 2886 species! Drosophila – the genus that possesses the genetic and developmental powerhouse D. melanogaster – contains approximately 2000 species***. It is clear that large, active research communities can readily work with diverse genera without problematic communication of their results. The sole argument of diversity is not strong justification for revising Anolis.
Perhaps some day taxonomy will abandon the binomial naming scheme derived from the Linnean classification hierarchy in favor of a more accurate system based solely on phylogenetic systematics. However, for practical purposes, we are simply not there yet. Anolis serves as a great example of where premature taxonomic revision could have far reaching consequences that can send biological research in multiple disciplines into severe turmoil.
Comments and discussion on the ideas I have shared above are welcomed and encouraged!
* This is not the say that critical evaluation of phylogenetic methods are not essential to the evaluation of taxonomic hypotheses. I will save evaluation of the Nicholson et al. analyses to those with greater experience working this these methods and those with an intimate knowledge of the proposed species groups.
** Beyond their proposed taxonomic revision the Nicholson team also reject the Anolis ecomorph concept. This idea will no doubt attract additional attention from the community. Stay tuned to Anole Annals for more on this issue.
*** A similar discussion to ours recently took place in the Drosophila community and many of these same concerns were expressed. O’Grady and Markow 2009 state that “such radical taxonomic revision is not advisable…as the literature and traditions are
so well established that any such formal reassessment would not be worth the confusion engendered.” After review and comments from the community the ICZN voted that taxonomic revision of Drosophila was “premature” and wisely left this diverse genus intact.
KIRSTEN E. NICHOLSON, BRIAN I. CROTHER, CRAIG GUYER & JAY M. SAVAGE (2012). It is time for a new classification of anoles (Squamata: Dactyloidae) Zootaxa, 3477, 1-108
This post serves as a lighthearted response to Jonathan’s earlier announcement and as an advertisement – perhaps endorsement – for some of the upcoming anole talks at Evolution 2012.
In his post Jonathan highlights recent comments by David Hembry that describe the blossoming of anoles into “field model organisms,” the ecological parallel of chicks, mice, and Drosophila which have long histories in laboratory studies. While the importance of anoles for Evolutionary Ecology is almost without question, I think that this stops short of describing the present and undeniable future of anole research. From my perspective, the roots of Anolis research are strong and wide, but its flower(s) has not yet fully blossomed.
Nearly one week has passed since I entered the Bahamas in search of Anolis brunneus, the Crooked Island anole. Since then I have also been joined by Michele Johnson and two students to help study the behavior and ecology of this poorly known species. I am happy to report that the lizards are treating us well and copious amounts of data are being collected each day. There are several developments that I thought might be of interest to the readers of this blog.
First, the anoles are everywhere! We have surveyed the entirety of the island and have found lizards in almost every habitat: in the sea grapes, in the forest, along the beach, along the arid southern coast, and even in the Bahamian Pines. The only habitat seemingly void of these fine lizards are the mangroves and coastal sea grasses. Green and brown anoles on this island seem to readily share the habitat as we regularly see them in close proximity but rarely fighting for perch space. Compared to A. sagrei, A. brunneus is mild mannered and extremely easy to capture making it a real pleasure to work with.
Anolis brunneus male
Today marked the beginning of my search for Anolis brunneus, the Crooked Island anole. As I discussed in my last post, this species has several unique qualities including its relatively elongate face and permanently pale disposition. I am happy to report that this rarely observed species has been located in all its drab glory. Over the next ten days I hope to collect data on this species’ distribution, ecology, and behavior. I will kick these reports off with a brief background about the island.
Crooked Island is one of the “Out Islands” of the Bahamas, located in the far southeast corner of the island chain. The island is a mix of salt marshes, sea grape, mangrove, and scrub trees rarely reaching more than a few meters high. Despite this seemingly serene picture, the island has a history of failed agricultural efforts, the largest being cotton plantations around the turn of the 19th century which covered ~10% of the total land area. At the peak of the cotton boom the island maintained approximately 1200 inhabitants, primarily slaves, but this has dwindled to only 300 today and continues to fall. The island now appears as an odd mix of both 19th and 20th century ruins that range from abandoned plantation homes to hurricane battered wood frames, many of which have been overtaken by the forests. Except for a few hotels that cater to bonefishermen, the island has virtually no tourism. Crooked island is home to several other lizard species including abundant A. sagrei and Leiocephalus, but more on this in a later post.
I am optimistic that we will come away from this field trip with substantial new data on this species. The one trick, we need to find them! Because of their pale color I have found them extremely difficult to find and track in the trees. Stay tuned!
Anolis carolinensis from south Florida. Photo courtsey of Neil Losin
Anolis carolinensis, the slender green anole from the southern United States is no stranger to most readers of this blog. This species is a model system for reproductive biology (here), is an emerging model for studies of development and Evo-devo (here and here), and is the first squamate lizard with a sequenced and annotated genome (here and here). Anolis carolinensis is, however, only one member of a diverse clade of lizards, though the natural history of many of these species is poorly understood relative to their popular cousin. Furthermore, the vast majority of carolinensis anoles* are known from few museum specimens meaning that robust descriptions of their morphology remain difficult to obtain.
I have recently become interested in the carolinensis series (for reasons discussed below) and have set out to better understand their biology. This post is meant to introduce readers to the diversity of carolinensis anoles and to put out a call for additional information that may be out there. While I have searched the wires for literature on these species, the community may know of hidden gems that have otherwise eluded me.
1) Species diversity and biogeography
The 13 species of the carolinensis subgroup and their localities are listed in the table below. Though many of these species were described in the late 19th and early 20th centuries the list continues to expand as Orlando Garrido and colleagues explore Cuban biodiversity, uncovering local variants to the more widespread species. Garrido has described four new species of Cuban green(ish) anole in the last 25 years and recent molecular analysis suggests that localized variation may be more common than previously appreciated. For example, Rich Glor and co-authors revealed several independently evolving lineages of A. porcatus that are correlated with Cuba’s geological history of partial island submergence (paper here).
The anoles of the carolinensis series. Specimen counts are based on a survey of the big five anole collections. Click to enlarge.
While several species are geographically widespread (A. porcatus, A. allisoni, and A. carolinensis***), the majority of this diversity evolved on relatively small Caribbean islands or in distinct regions of Cuba.
For those of us that study embryonic and juvenile development this is an exciting time. The first anole eggs of the season are here!
The prize for first egg of the season goes to Anolis distichus. Fifteen females were collected in Miami one week ago ago and I collected 11 eggs from their cages yesterday. A. carolinensis, A. sagrei, and A. cristatellus seem to be off to a slower start. Of the 12 A. sagrei females collected I only found two eggs while the other species have yet to produce any. My fingers are crossed that egg production picks up soon.
Is anyone else out there having any early season luck? Which species? Are people in the field observing regular mating behaviors now?