Category: New Research Page 30 of 66

Mean CTmin for invasive (gray) and native range (green) populations of Anolis sagrei.

Most anole enthusiasts are familiar with the brown anole, Anolis sagrei, because it is a highly successful invader. Although it can be found as far away from its native Cuba (and nearby islands) as Hawaii and Taiwan, most of what we know about invasive populations of this species come from work conducted in Florida. A recent study by Jason Kolbe and colleagues demonstrated that physiological traits vary with latitude in A. sagrei from Florida. Specifically, cold tolerance (CTmin) and desiccation resistance were lowest at higher latitudes in Florida. Tamara Fetters, a graduate student in Joel McGlothlin’s lab at Virginia Tech, supplemented this work by adding data from a native population of A. sagrei found on the island of San Salvador in the Bahamas.

Box plots showing rates of evaporative water loss in invasive (gray) and native range (green) populations of Anolis sagrei.

Tamara found that mean CTmin for A. sagrei from the Bahamas was close to 12°C, which was significantly higher than in Tifton, the most northerly population from Jason Kolbe’s study, but not significantly different from the lower latitude populations in Orlando and Miami. Similarly, she found that desiccation tolerance in native range A. sagrei was significantly higher than in lizards from Tifton, a result that she attributes to the lower relative humidity found at higher latitudes in Florida. Tamara’s future goals include measuring more physiological traits, such as oxygen consumption and heat tolerance (CTmax), along with morphological traits associated with desiccation resistance (scale number and scale area), for various invasive and native populations of Anolis sagrei.

Evolution 2014: Ecomorphological Analysis of Scale Number in Anoles

By Martha Muñoz

On June 21, 2014

In All Posts, New Research

Hanna Wegener talks about Anolis scales at Evolution 2014.

Talks are underway at Evolution 2014 and anoles are already off to a strong start! Early this morning, Hanna Wegener, a Ph.D. student at the University of Rhode Island, discussed some of her work on the diversity in scale size in Anolis lizards. The work she presented was conducted in collaboration with Gabe Gartner and Jonathan Losos from Harvard University. Hanna started by discussing the adaptive radiation of anoles in the Caribbean. As a community, she said, we know quite a bit about how certain morphological traits, namely skeletal dimensions and lamella counts (i.e., number of toe pad scales) differ among ecomorphs and among different climatic habitats. Scale number, however, remains comparatively unexplored in anoles. For her study, Hanna examined ventral and dorsal scale counts in anoles. Her sampling strategy was impressive – by mining the collections in the Museum of Comparative Zoology at Harvard University, she was able to get scale counts for well over 100 anole species, and Caribbean anoles were particularly well represented in her dataset.

She first sought to examine the relationship between scale number and climate. There are prevailing ideas regarding how scale size and number should relate to climate. Specifically, Michael Soulé and Charles Kerfoot have posited that larger scales are advantageous in hot environments because their greater surface area increases radiative efficiency. Larger scales are also thought to reduce water loss in dry environments. Thus, lizards in hot, dry environments should have fewer, larger scales than lizards in cool, wet environments. Hanna found a positive relationship between scale number (both dorsal and ventral) and precipitation, but she did not find a significant relationship between scale number and temperature.

Hanna showing the variation in scale number and size among anoles. The top two rows show dorsal scales, whereas the bottom two rows show ventral scales.

Hanna then asked whether scale number relates to structural microhabitat use. Here the study became much more exploratory and exciting because, if there is little known about the relationship between climate and scale number, there is even less known about the relationship between scale number and microhabitat use. Hanna found significant differences among ecomorphs in scale number. She found that higher perching ecomorphs, such as crown-giants and trunk anoles, tended to have more, smaller scales. Lizards that perched lower and used broad surfaces, such as trunk-ground species, tended to have fewer, larger scales. Although the precise mechanism underlying this relationship remains unknown, Hanna posited that aspects of microclimate, such as temperature, might vary with structural habitat, which may in turn drive scale number patterns. She also suggested that the observed patterns of scale number variation might represent correlated evolution, such that scale number covaries with a trait that relates to differences in structural microhabitat use. Hopefully Hanna’s study leads to more research on the significance of scale number in anoles and other lizards.

Anoles (and Other Lizards) at SMBE 2014

By Anthony J Geneva

On June 7, 2014

In New Research

The annual meeting of the Society for Molecular Biology and Evolution meetings start this weekend in San Juan, PR and there are a number of talks and posters to appeal to the squamatophile.

There are three presentations from AA contributors (Marc Tollis and Tony Gamble) using anole genomic data, as well as posters and talks on phylogeography of Puerto Rican Sphaerodactylus, and genome-scale studies of Sceloporus, skinks, and snakes. You can see the full list after the jump.

Evolution Program Released: Anoles Are Back in Strong Force

By Martha Muñoz

On May 29, 2014

In New Research

I may have given the Evolution 2014 logo an Anolis upgrade.

It’s that time of year again! The annual Evolution meeting is upon us. In just under a month, scientists from around the world will converge on Raleigh, North Carolina to learn about new and emerging trends in evolutionary biology. As with the Society for Integrative and Comparative Biology meetings, anoles have had a strong presence at Evolution. It appears that this year will be no different. A quick search for talks including the terms “anole” or “Anolis” yielded seven presentations, and so this meeting should be quite fruitful for those of us interested in what’s new and exciting in Anolis. You can view the list of scheduled presentations here – simply put Anolis into the keyword search at the bottom and all seven presentations will be displayed. Or just look below. As in previous years, we’ll be blogging live from the conference, so stay tuned.

Female Preference in the Brown Anole

By Sarah Flanagan

On May 28, 2014

In New Research

As a senior in college I wanted to study courtship behaviors, and the brown anole (Anolis sagrei) piqued my interest. In going through the literature, I noticed that some studies reported finding evidence for the presence of female choice in brown anoles and others reported that female choice didn’t occur in the species. So I decided to see if females exhibited a preference for males based on two different characteristics: male physiology and male territory quality, each of which would provide females with different benefits. I expected that females would choose males based on territory quality, because females usually mate with the males whose territories overlap theirs in the wild.

I tested for female preference in two different choice experiments using anoles that I ordered and had sent to my college, Colby College, in Maine. I was given access to a small storage closet (which I cleaned out) in the basement of Colby’s biology building in which I kept my crickets and anoles. To test for differences between males with different physiological traits, I tested male endurance by placing them on a treadmill and running them until they couldn’t run any longer. This was perhaps one of the most stressful parts of the experiment for me, since the lizards really didn’t like being put on the treadmill, so during this part of the experiment I got to chase many lizards around the room.

A brown anole running on a lizard treadmill

I then paired similarly-sized males with very different running times to see if females spent more time with one male over the other. For the preference tests, the males were tethered to posts in a mate choice box originally constructed for zebrafinches, and the females were able to run freely through the box.

In the territory tests, rather than pairing males with different endurance scores, I randomly placed males on the side of the box with many plants and twigs, or on the side without. In both tests, I recorded the amount of time females spent on either side as well as the behaviors of the males and females (I watched many hours of video to score behaviors).

Mate choice arena for the territory quality experiment

My results were somewhat surprising; I found that in both experiments the more active male was the most preferred one. This was contrary to my prediction, especially since our measure of activity included all male behaviors, not just courtship behaviors. This is not surprising in the broader scheme of mate choice, since active mates are often preferred, and it’s interesting to see how anoles fit into the bigger picture of mate choice and sexual selection in general. This study is now published, so check it out if you’re interested in the details! Please feel free to contact me if you have any questions or would like a copy of the pdf.

Bahamian Lizards Reduce the Amplitude of Their Headbobs in the Presence of Predators

By DavidSteinberg

On May 21, 2014

In New Research

The Anolis literature is replete with examples of lizards altering the properties of movement-based displays in response to fluctuations in environmental conditions. Anoles modulate head-bob amplitude based on social context (Fleishman 1988) and social spacing (Stamps and Barlow 1973, Steinberg & Leal 2013), and head-bob speed based on background vegetation motion (Ord et al. 2007) and many other habitat variables (e.g., Ord et al. 2010). Our recent paper adds predation pressure to this growing list of factors that might affect the signal properties of anoles.

Anole Performance Meta-analysis!

By Annie Cespedes

On May 17, 2014

In New Research

http://onlinelibrary.wiley.com/doi/10.1002/ece3.528/full

Example of a three-task Pareto front in a 3D morphospace, Figure 9 in Sheftel et al 2013.

I want all of your old performance data.

Who am I? I am a Ph.D. student and the thrust of my dissertation project is to arrive at a better understanding of how selection, trade-offs and constraints act on suites of performance traits, leading to adaptive phenotypic shifts in populations and, ultimately, evolutionary change. I am particularly interested in constraints imposed on performance evolution by intralocus sexual conflict, and in the relationship between preferred and maximal performance.

What am I going to do with it? I am conducting a meta-analysis of existing performance data, which involves mapping suites of performance traits onto lizard morphospace and fitting a multivariate response surface. This surface can then be used (by everyone!) to predict trade-offs between different types of performance traits in various selective contexts, and to identify regions of morphospace associated with performance peaks and valleys. These areas, and the taxa that occupy them, would thus be of interest in terms of looking for behavioral compensation or other solutions. Conversely, areas of morphospace devoid of extant taxa may be indicative of insurmountable constraints or something even more interesting. Such insights will, I hope, inform more exploratory, experimental and comparative avenues of investigations.

I’m focusing on Anolis in particular to start with, and I’d like to quantify the relationships between the span of extant anole morphology and any and all whole-organism performance traits. But to do this, I need data! Lots and lots of data! And I don’t have enough 🙁 Which means I need your data.

What I need:

Raw data¹ from previously published studies involving performance trait data along with morphological² measurements for any and all Anolis species would be very useful and much appreciated. The more coverage of morphospace/performance space, the more useful and powerful the model!

If you’ve ever measured any of the following performance traits in anoles, you’ll probably be getting a grovelling email from me, but just in case you have somehow escaped my scrutiny, or don’t want to wait for the grovelling email, here is what I am looking at:

bite force
sprint speed
acceleration
endurance
exertion
maneuverability
jumping
climbing
clinging

Performance data for multiple traits measured in the same individual will be the most informative, but I will also need plenty of data on single performance traits. I have few other standards (as far as this project goes), so anything will be useful!

Thanks so much for reading this far! I sincerely hope this piques your interest and inspires you to share your work with me. I will of course be open to discuss any and all aspects of data-sharing, collaboration and subsequent use or availability of the data. All contributing authors will be acknowledged and papers cited, or whatever else is necessary! If you have anything you would like to contribute please feel free to contact me directly @ acespede@uno.edu.

¹I can use raw data files, in whatever format (e.g., .xls, .txt., .sys, .jpg of a lab notebook or rum-stained bar napkin).

²I would be happy with anything from SVL-only to comprehensive measurements for individual limb components, toe pad area, etc. Body size and limb measurements are ideal!

(Figure from Sheftel, H., Shoval, O., Mayo, A., Alon, U. 2013. The Geometry of the Pareto front in biological phenotype space. Ecology and Evolution, 3(6): 1471-1483)

Estrogen Pathway Is Responsible for Facial Elongation

By Jerry Husak

On April 19, 2014

In New Research

Why the long face?

When most people think of vertebrate sexual dimorphism (differences between the sexes), they think of elephant seals or red deer. Most of us here, of course, think of the pronounced dimorphism in size and shape in many anole species. Indeed, anoles have served as excellent model systems for the study of sexual dimorphism, particularly the evolutionary forces that give rise to it. Although there has been significant progress since Darwin in our understanding of why sexual dimorphism evolves, we have made less progress in the HOW. That is, what mechanisms during development give rise to what are often extreme differences between the sexes when their genomes are so similar?

When we think of vertebrates where males are larger or shaped differently than females, and have weapons or ornaments, we almost immediately think of testosterone as a mechanism underlying the sex differences. Once sexual maturity happens, the testes start cranking out testosterone, thus causing a change in the male’s phenotypic trajectory. While there is certainly evidence for circulating testosterone to have this effect in some lizards, is this always the case, and does it apply to specific body parts and not just overall size? Aside from the circulating hormone, how are receptors involved in the development of dimorphism? In a new paper by Sanger et al., a novel developmental pathway of sexual dimorphism is described for lizards in the carolinensis clade, which are striking in their elongation of male faces relative to females.

Figure 1a. from Sanger et al. (2014), showing the differnces in head shape dimorphism among anole clades. Note the long male face in A. maynardi, a member of the carolinensis clade.

Figure 1a. from Sanger et al. (2014), showing the differences in head shape dimorphism among anole clades. Note the long male face in A. maynardi, a member of the carolinensis clade.

Sanger et al. tested whether sex differences in several different pathways led to the observed head shape dimorphism in A. carolinensis compared to two non-carolinensis species (A. cristatellus and A. sagrei) that exhibit shorter male faces. They show, using a combination of developmental and molecular genetic techniques, that the extreme elongation of male heads in carolinensis lizards is not due to an androgen pathway (i.e., testosterone) or the somatropic axis (i.e., insulin-like growth factor). Instead, they found a significant shift in the estrogen pathway. Specifically, at sexual maturity, males decrease expression of estrogen receptors (erβ), which is the beginning of a signaling cascade, ultimately resulting in up-regulation of genes involved in skeletogenesis in the skull of males.

Figure 4 from Sanger et al. (2014), showing the molecular pathway underlying facial elongation in A. carolinensis.

This identification of a novel mechanism for the development of sexual dimorphism will certainly stimulate further evo-devo research in anoles and beyond. For starters, is the same pathway responsible for male facial elongation in other species in the carolinensis clade, or are more ‘traditional’ mechanisms operating there? This important research highlights that investigators need to consider all aspects of signaling systems, including circulating hormones, their receptors, and signal cascades that result from activation of a particular pathway. Clearly this paper by Sanger et al. is an excellent step in the right direction for understanding how developmental pathways lead to adult difference in anoles, and it will also steer other investigators to consider a diversity of developmental mechanisms in their quest to elucidate how adults end up the way they do.

Sanger TJ, Seav SM, Tokita M, Langerhans RB, Ross LM, Losos JB, Abzhanov A. 2014. The oestrogen pathway underlies the evolution of exaggerated male cranial shapes in Anolis lizards. Proceedings of the Royal Society B 281:20140329.

Decoupled Muscle Activity and Kinematics in Green Anoles (Anolis carolinensis): New Research by Kathleen Foster and Tim Higham

By Kathleen Foster

On March 26, 2014

In New Research

Anolis carolinensis. Photo taken by Kathleen Foster.

Anoles are the indisputable poster children of ecomorphology. Morphological, behavioral, and performance data support classification of Anolis species into discrete ecomorphs on the Greater Antilles islands. In a large part, the basis of this classification is due to variables (e.g. limb length) that relate to differing locomotor abilities (i.e. speed and/or stability) on the various substrates that comprise the different areas of the arboreal habitat. However, until recently, we knew nothing about how the muscles that power locomotion in these species relate to their ability to cope with the challenges of moving in these different microhabitats.

In a recent paper in Proceedings of the Royal Society B, we used a combination of electromyography and 3D high-speed video to examine the impact of perch diameter and incline on limb kinematics and muscle activity in Anolis carolinensis. Our previous study in the Journal of Experimental Biology found a number of kinematic changes (e.g. increased limb flexion and depression) associated with increased stability on narrow surfaces, and we hypothesized increased recruitment in the muscles associated with those movements. Interestingly, this was not the case. Despite considerable kinematic modulation with change in perch diameter (63% of the 32 kinematic variables were significantly affected by perch diameter), there was very little change in muscle activity (2% of the 100 muscle activity variables). This decoupling of kinematics and muscle function raises a number of very interesting questions relating to the sensitivity of these muscles to changes in operating length and the degree to which this species is specialized for a particular microhabitat. It also highlights the complexity of the physiological basis of animal locomotion and emphasizes the need for caution when attempting to infer motor control from kinematics and vice versa.

An additional result that may significantly impact identification of habitat preference in Anolis lizards relates to the importance of variability, as opposed to magnitude, of muscle activity in describing the differences in how this species handled the different substrate conditions. Specifically, the muscles examined were less variable on the broad perch compared to the narrow perch and on the vertically, as opposed to horizontally, inclined perch. Locomotor stereotypy is generally believed to reflect locomotor specialization, although reduced variation of in muscle activity may also be achieved as a byproduct of near-maximal muscle recruitment. However, we have little support for this second option, as the muscles were neither approaching maximal stimulation nor vastly different in overall magnitude or recruitment. Therefore the greater stereotypy of muscle activity seen in the green anole as it moved on the broad, vertical condition may reflect a physiological preference for tree trunks, rather than the narrower and shallower substrates that comprise (on average) the trunk-crown region to which it is traditionally assigned.

It is clear that there remains a wealth of knowledge waiting to be unearthed in the Anolis system and this paper barely scratches the surface. It emphasizes how little we understand about the complex nature of animal locomotion and the relationship between the muscles that power locomotion and the movements we observe in the field. And the possibility that variability of muscle activity might be a useful tool to identify functional preference for microhabitat is tantalizing and deserves further attention, especially if it can be applied usefully to mainland Anolis species. The remainder of my dissertation will focus on fleshing out these and other aspects of muscle function through the comparison of ecomorphs of the Greater Antilles.

Kathleen L. Foster & Timothy E. Higham. (2012). How forelimb and hindlimb function changes with incline and perch diameter in the green anole, Anolis carolinensis. Journal of Experimental Biology 215: 2288-2300. (DOI: 10.1242/jeb.069856)

Kathleen L. Foster & Timothy E. Higham. (2014). Context-dependent changes in motor control and kinematics during locomotion: modulation and decoupling. Proceedings of the Royal Society B 281: 20133331. (DOI: 10.1098/rspb.2013.3331)

Transgenerational Effects Of Nutrition Observed In Anolis sagrei

By Thomas Sanger

On March 25, 2014

In New Research

Mothers affect the quality of their offspring. As humans, this seems obvious. For example, expecting mothers often take prenatal vitamins, limit their consumption of certain foods, and avoid kitty litter knowing that these minor environmental factors can affect the normal development of the fetus. Related statements could be made for the relationship of a mother and child after birth. Understanding the precise effects that parents have on their offspring has been of great interest to biologists from many disciplines as they disentangle the genetic and environmental factors that underlie differential survival and reproduction for individuals within a population (fitness). Because Anolis lizards can be easily maintained in captivity and their eggs readily manipulated they provide a useful model for the examination of maternal effects. Warner and Lovern took advantage of these qualities and tested the role of maternal body condition on offspring quality in the brown anole, Anolis sagrei.

A. sagrei from Cayman Brac

Nutritional stress is a well-studied example of how maternal condition may affect juvenile quality; if the mother is malnourished the quality of her egg yolk may suffer, which, in turn, affects embryonic development. The authors tested this hypothesis in A. sagrei by manipulating the amount of food gravid females received, feeding approximately 168 crickets per lizard in a “high-prey” treatment versus 84 crickets in a “low-prey” treatment distributed over 11 weeks. During this time the authors carefully assessed the number and size (mass) of the eggs and, subsequently, the quality (mass-and-snout to vent length) of the hatchlings. Impressively, the authors didn’t stop there. They also experimentally manipulated the amount of nutrition in a subset of eggs by removing yolk with a syringe. Followed by a battery of statistical models, this study is quite a nice physiological analysis that has evolutionary implications.

When comparing the two diet regimes, Warner and Lovern found that body condition does affect the quality of offspring; females maintained on the “low-prey” diet produced eggs 6.6% smaller than females raised on the “high-prey” diet. In turn, smaller eggs also tended to hatch more quickly and smaller eggs produced smaller hatchlings, both probably due to the lower amount of available nutrition (paradoxically, neither incubation time or hatchling mass was directly correlated with maternal prey availability). Low prey availability also results in hatchlings with slower growth rates. The experimental reduction of egg yolk supports the results of the prey availability study: hatchlings from yolk-reduced females were 8% shorter and 23% lighter and grew more slowly than those hatched from unmanipulated eggs. It is clear from their results that nutrition has an effect on hatchling quality well into life, after the obvious maternal effects have passed. There are a number of other interesting correlations (and statistical caveats) described within the text that may also be of interest to some readers.

Figure 5 from Warner and Lovern 2014.

What is becoming clear from studies like these is that environmental stressors can have lasting effects on organismal development that transcend generational boundaries. Mechanistic studies, such as those on the American alligator, illustrate that these effects are mediated by heritable methylation patterns of key regulatory genes. The stressors do not need to be long lasting; physiological responses can result from acute events that occur within key developmental windows, often when a particular organ is maturing. While stressing the embryo too far results in abnormal embryonic development, more subtle effects may not arise until late in life or subsequent generations. Anoles, and A. sagrei in particular, may provide a number of opportunities for environmental health research in the future. Studies such as the one described above could be performed to more precisely dissect the organ-specific effects of maternal nutritional stress or whether the effects dissipate with age. Similar to the alligator studies, eggs laid in polluted soils may allow opportunities for developmental toxicology research. Growing genomic resources may allow for examination of genome-wide and gene-specific methylation patterns within and outside of polluted habitats. The possibilities are broad and the impact cannot be predicted at this time, but the potential is there for much more detailed mechanistic research on the relationship between developmental physiology and the environment.