Category: New Research Page 53 of 66

The Caribbean skink radiation. Islands identified by name have (or had) mabuyine skinks; others--notably Cuba--do (or did) not.

Think Caribbean lizard diversity and you think of anoles, dwarf geckos, perhaps curly tailed lizards and whiptails. But skinks don’t generally come to mind. Heck, I almost never see skinks in the Caribbean and, anyway, their diversity is very low, with only six Caribbean species.

Previously considered conspecific

Until now. In a recently published monograph, Hedges and Conn have scrutinized the genus Mabuya, using both molecular and morphological characters, and have more than doubled the number of species, from 26 to 61, which they have broken into 16 genera (and, as a sidenote, they also split the family Scincidae into seven families). That so many species went undetected is perhaps not surprising, in that Mabuya, like most skinks, all look alike, with very few characters available to distinguish them. Moreover, a trend of species lumping has occurred historically, obscuring sometimes great differences among taxa, as illustrated in the photo to the left.

Of the 61 species, 39—in six genera—occur on Caribbean islands. Most occur on a single island, and most islands only have one species, though as many as three occur on Hispaniola and St. Thomas, and two on a number of islands. Oddly, Cuba has none. Like anoles, to which they no doubt aspire,

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Lizards have become a staple of laboratory studies of locomotion. A standard approach, honed to perfection over 30 years of such work, is to get a lizard to run down a narrow trackway or on a dowel to determine how fast it can run and, in recent years via high speed video, to see exactly how the different limb elements move. Questions that one might ask include whether long-legged lizards run faster than their short-legged compatriots, whether species can run faster on broad surfaces as compared to on narrower supports, or whether the loss of a tail affects sprint speed. In fact, the sort of questions one might ask about lizard locomotion are virtually endless.

These studies have one Achilles heel, however, Most such studies focus on examining maximum speed of the lizard, but how can one ensure that lizards are actually running full tilt? The nagging fear has always been that differences in speed might result not for different capabilities, but rather as a result of differential motivation–some lizards just want it more than others.

But how can one elicit maximal speed or investigate whether a lizard is holding back? One approach to this question was revealed in a recent paper in J. Herp. Jones and Jayne tested whether a loud noise might cause a lizard to run faster and the answer is: yes, when subjected to repeated loud noises, lizards in experimental race tracks do, in fact, run faster.

And just what kind of loud noise? Let’s let junior author Bruce Jayne explain the genesis of the study:

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Although devoted to all things Anolis, Anole Annals strives to keep its readers updated on relevant findings concerning other lizards. In that vein, we’ve just learned of a newly completed thesis on lacertid lizards on European islands by Anna Runemark at Lunds University, under the supervision of Erik Svensson. Here’s the English summary of her thesis, from this page, and some remarks from Erik here. Her defense is on May 25th. Good luck, Anna!

“Islands are cradles for new biodiversity and provide natural laboratories for the study of population divergence. In my thesis, I investigated the role of different evolutionary processes in the population divergence in the Skyros wall lizard (Podarcis gaigeae), a species where islet populations have strongly diverged morphologies. I used replicate islet populations and their respective most proximate mainland populations to investigate how divergence has proceeded following the isolation of the islets. First, I combined bathymetric maps with sea level curves and molecular inferences based on Bayesian statistics to investigate the biogeographical history of populations. I found that islet populations have become isolated by vicariance following sea level rises during the last thousands of years, and no significant gene flow between populations. To investigate which processes are affecting population divergence, I studied patterns of divergence in coding genetic variation, traits assumed to be under simple Mendelian inheritance, morphological and behavioral traits. A clear pattern of parallel adaptive divergence in the islet environment emerged for traits mainly subjected to natural selection. Islet lizards were larger, greener and less prone to escape. Islet lizards were also less cryptic in their environments than were mainland lizards. Moreover, between-population variation in size and color was larger for islet- than for mainland populations. These patterns are indicative of a predation release. I also found that islet lizards have relatively wider and differently shaped heads as well as a stronger bite force in relation to mainland populations. Data on available food and realized diet suggest that these changes are adaptations to harder island diet. Together these data suggest that predation release and selection for a diet change have interacted and jointly driven the evolution of larger body sizes on islands.

No general pattern of parallel divergence was found for traits subjected primarily to sexual selection. Instead, divergence in throat color morph frequency and sex pheromone composition were significantly correlated with neutral genetic divergence. This indicates that stochastic processes such as genetic drift have contributed to divergence of these traits. I also investigated if mate preferences for pheromones, throat color and body size could be driving population divergence. I found no population differences in preferences for throat color and body size, suggesting that mate choice does not drive divergence in these characters. Islet populations did, however, prefer scent from islet lizards, whereas mainland lizards were less discriminatory. This implies that there could be some mate discrimination against mainland lizards that disperse to islets. 

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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?

Ok, not a parasitic worm of anoles, but it got your attention! Photo from http://childhealthproblems.com/images/head-of-helminth.jpg

In a gargantuan recent paper in Comparative Parasitology, Bursey, Goldberg, Telford and Vitt report new data for 13 Central American anoles and summarize what is known about helminths through all of anoledom. Before getting into the details, though, it may help some of our readers to explain what a helminth is. In short, helminths are parasitic worms, such as nematodes, flukes, and tapeworms; anoles—and many other animals—are commonly infested with them.

Prior to this study, helminths had only been reported in 10 Central American anoles. However, taking advantage of the collections of Telford and Vitt, dating back to late 1950’s, the researchers examined 426 anoles of 13 species, basically opening up museum specimens to see what surprises awaited. The result was 1026 parasites found in 173 of the specimens.

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The Bay Islands proper consist of a crescent of four land-bridge islands lying approximately 50 km off the northern coast of Honduras in the Caribbean Sea.  About halfway between those islands and the coast lies a smaller sub-archipelago, known as the Cayos Cochinos (or ‘Hog Islands’), which consist of two larger islands (Cayo Mayor and Cayo Menor) and 13 smaller cays (see the map below).  The Cayos Cochinos are famous in the commercial reptile trade for their endemic populations of insular-dwarf ‘pink’ boa constrictors.

The Bay Islands and Cayos Cochinos of Honduras. For scale, Cayo Menor and Cayo Mayor are about 3 km apart. Adapted from Green (2010).

I’ve had the pleasure of conducting herpetological research in the Bay Islands since 2007 thanks to support from a UK-based conservation organization called Operation Wallacea, and a generous team of researchers (Chad Montgomery, Bob Reed, Scott Boback, Steve Green, and Tony Frazier) that have been working on the boa and Ctenosaura populations there for several years, and were nice enough to get me involved.  And while the Bay Islands have gained some notoriety for their exotic snakes, another local squamate has gone (almost) entirely unnoticed.  I’m alluding to, of course, the anoles.  In 2007, when I was helping Chad Montgomery with his Ctenosaura melanosterna project on Cayo Menor, I began to notice just how abundant the anoles on that island were.  The little guys seemed to be on almost every tree in the interior of the island.  After asking around and doing a few literature searches, I started to realize just how untouched, and potentially interesting, this system really was.

Two anole species occur in the Cayos Cochinos, Anolis lemurinus and Anolis allisoni.

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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,

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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).

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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.