Category: New Research Page 54 of 67

Several years ago I was involved in a study showing that the dewlaps of individual male green anoles change size over the course of a breeding season, increasing in area from winter to spring and then shrinking from spring to winter. This result was first noted in the field and verified in the lab, and is not a statistical artefact – individual dewlaps really do change size!

Shortly after that study appeared I found myself in Australia doing postdoc work on crickets. During that time I gained an appreciation for life-history and the battery of approaches, ranging from artificial diets to mating schedule manipulations, which researchers use to expose resource allocation priorities in animals. (On a related note, I also gained an allergy to crickets). When I returned to the lizard world I started thinking about dewlaps and resource allocation, and I wondered if it might be possible to apply some of these life-history techniques to anoles to figure out the mechanisms underlying the incredible growing/shrinking dewlaps.

It turns out that not only is it possible, it’s actually pretty easy, and my research group was recently able to conduct a simple dietary restriction experiment that yielded some unexpected results. We wanted to test whether dewlap size is affected by resource availability,

Read More

httpv://www.youtube.com/watch?v=r33UMVk1o5s&feature=email

As a scientist in life sciences, I have always tried to highlight the existence of laws. It seems to me that all science should be predictive. Once we are interested in locomotion, the first idea that comes to mind is the following: are there any laws of locomotion that transcend forms, species? Is it possible to predict locomotion of any species to the knowledge of environmental constraints it faces (Legreneur et al., 2012)?

I am not a herpetologist. Over 15 years I have worked on humans, and especially high-level athletes and the elderly. I demonstrated in humans that the trajectory of any point controlled by the central nervous system was still as linear as possible. This point is either the fingertip during a pointing or grasping task, or the body center of mass during locomotion, e.g. during the takeoff phase of a jump. Since most joints move in rotation, and that the controlled point displaces through a linear path, it is necessary to dephase the rotating joints to transform the rotation kinematic energy into linear energy. Finally, for transmiting force from the body to the substrate, for example from the hip to the ground during the jump, the joints move in a proximal-to-distal manner, i.e. the extension of the hip precedes the ones of the knee and the ankle.

To demonstrate that these laws observed in humans were applicable to all terrestrial tetrapods, I am interested in two phylogenetically very distant arboreal jumpers, i.e. a prosimian, Microcebus murinus, and a squamate, Anolis sp. I reproduced with these two species the same experiments that I conducted on humans, i.e. leap up to maximum and submaximal heights. Thus I demonstrate that the coordination observed during take-off in maximal leaping were identical in humans, Microcebus and Anolis (Legreneur et al., 2010; Legreneur et al., 2011; Legreneur et al., 2012).

Read More

The University of Chicago Press has recently published another outstanding new book for comparative biologists.  Charles Nunn‘s The Comparative Approach in Evolutionary Anthropology and Biology provides insightful reviews of methods for ancestral character reconstruction, phylogenetic tests for character correlation, phylogenetic diversification analyses, and many other topics.  Nunn’s book seems well-suited to a broad range of readers.  It seems tractable for novices (the second chapter explains what a phylogenetic tree is), and those with math anxiety won’t be deterred by dense discussions of mathematical or computational algorithms.  At the same time, seasoned comparative biologists will likely appreciated Nunn’s fairly comprehensive coverage of alternative methods and their relative strengths and weaknesses.  Although most of Nunn’s examples are from anthropology, the general lessons in this book are likely to be of interest to many anole biologists and the examples from anthropology are often insightful and thought provoking.  To top it all off, the book is accompanied by really nice webpage called AnthroTree that features tutorials and worked examples.

Springer recently published a new and dramatically expanded version of Pardis’s book Analysis of Phylogenetics and Evolution with R.  This book is a great way to teach yourself some of the amazing techniques available for phylogeneticists and comparative biologists via the R statistical computing environment. With 386 pages, the new edition is nearly twice as large as the previous version (211 pages).  Countless new methods are covered, and many problems with the previous edition are remedied.  In spite of the expansion and improvements, the sticker price is actually lower on the new edition ($65) than it was on the old edition ($75).  You can pick up a copy for around $50 at places like Amazon.com.  This book should be considered required reading for anyone doing modern phylogenetic and comparative analyses.  If you need anoles to inspire an interest in learning R, I’ll be posting shortly on some R tutorials that use anoles as case studies.

Anolis carolinensis mating. Photo by Michele Johnson from Wade (2012). Insets: Upper, vertebral column of green anole around pelvis and tail; lower, hemipenis musculature.

Juli Wade has just published a review paper in which she sings the praises of anoles as a group to study the integration of behavior, anatomy, endocrinology and molecular mechanisms in vertebrate reproduction. She notes that a number of model systems exhibit, but synthesis is hindered because courtship and copulatory systems have been studied in different groups and, among studies of courtship biology, very disparate structures have been examined (e.g., bird syrinxes, frog larynxes, fish swim bladders) making comparative analysis difficult.

Anoles to the rescue! Wade notes: “Anoles offer some advantages over these other model systems. A long history of research into the hormones, brain and behavior exists for one species, the green anole (Anolis carolinensis), and a substantial amount of data is also available for the brown anole (A. sagrei). These studies indicate that the hormonal regulation of behavior appears quite similar in these two species of anoles. The genome of the green anole has recently been sequenced, which greatly facilitates investigations at the molecular level. Two features, however, provide unique power for the investigation of mechanisms regulating structure and function.

First, three sexually dimorphic systems exist within the same individuals – portions of the limbic forebrain, which control higher level or more motivational aspects of sexual behavior, and both courtship and copulatory neuromuscular systems, all of which lend themselves to investigations in the field and laboratory. Second, more than 350 species of anole lizards span the Southeastern US, Caribbean islands and Central and South America. Information on the behavioral ecology and phylogenetic history of many of these is accessible. And, while limited data on the neural and muscular structures regulating courtship and copulation are currently available, it is clear that species across the genus exhibit beautiful variation in the degree of sexual dimorphism in morphology on a gross level. Anole lizards therefore represent a terrific opportunity for more detailed investigations from an evolutionary perspective.”

The good folks at Science magazine are giving away copies of the recent paper for free! Get yours today. Just click here.

Cover of Science, 2 March 2012

Anoles have gotten the cover again! This time it’s on tomorrow’s issue of Science for this work by Jason Kolbe and colleagues, covered here on Anole Annals. The photograph of A. sagrei is by Neil Losin, whose photo- and videographic works have been profiled on Anole Annals several times before.

Green anoles can change from green to brown. Occasionally, they do it only part way. Photo from http://www.floridagardener.com/img/critters/Greenanole.jpg

Widely, if inaccurately, known as the American chameleon, Anolis carolinensis is renowned for its ability to change color from a sparkling emerald to a deep brown. Surprisingly, we don’t really know what factors determine whether a particular lizard chooses to be green or brown at a particular time.

Here’s what I had to say about it in Lizards in an Evolutionary Tree (pp. 279-281; I’ve omitted most references here):

“In theory, we might expect green anoles to match their background, turning green when in vegetation and brown when against a woody surface. Although widely believed, this idea is not strongly supported (reviewed in Jenssen et al., Herp. Monographs, 1995).

Read More