Incubation temperature is an important factor in development for anoles (and other ectotherms). Thom Sanger, a professor at Loyola University in Chicago, IL, presented his research on how high temperatures affect brain formation in developing anole embyros. With the help of undergraduates and a high school summer intern, Dr. Sanger found that when developing eggs were heat-shocked, many embryos were lost (75%), but for those that survived, forebrains became smaller (In the figure, A is normal and B is deformed). Interestingly, malformation of the forebrain affects the size and shape of the face, and so surviving heat-shocked embryos exhibit cranial malformations. As Sanger continues his research, he will follow a neural degeneration hypothesis, which boils down to (no pun intended) the idea that thermal stress increases the rate of cell death, and the amount of cell death affects facial shape. While the effects of high temperature may seem alarming, Sanger notes that this does not happen very often in nature; females are generally pretty good at selecting suitable nest sites. But, because development is similar across reptile taxa, anoles can be an excellent model system to inform predictions about what may happen to species that are in danger.
Author: Andrew Battles
The color change from a bright, vibrant green to a dull, muddy brown is one of the most characteristic qualities of the green anole (Anolis carolinensis) (I am aware that some dewlap enthusiasts may take issue with this statement). Given the dramatic differences between the colors, Daisy Horr, a Junior in the Johnson Lab at Trinity University in San Antonio, TX, wondered how social behavior and body temperature may influence body color, and whether these relationships differ between males and females.
First, Daisy observed green anole social behavior in Palmetto State Park, TX, and found that males exhibited green body color more frequently than females, and males that performed more pushup and head bob displays also changed colors more frequently (between green and brown). She also found that females were more often green during social interactions.
Because green anoles are ectothermic, more commonly known as cold-blooded, ambient temperature plays an important role in nearly every aspect of their lives. Therefore, there might be a relationship between body color and thermoregulation. Daisy spent a lot of time searching the Trinity University campus for green anoles, and measured body temperatures, the temperatures of the perch on which she found them, and the distance to the nearest alternative perch (a measure of exposure). While she did not find any association between body color and temperature, she did show that males used warmer substrates than females, and that males were typically more exposed (greater distance to the nearest perch). Additionally, she found that males are generally greener than females throughout the day.
Daisy plans to pursue graduate school after she finishes at Trinity University, and we all hope she continues to contribute to anole research! Graduate advisors, you don’t want to miss out on a fabulous researcher!
(This post’s author’s diploma from Trinity University does not affect his assertion that Trinity graduates are among the best minds in biological research.)
Kathleen Foster, a Ph.D. student in Tim Higham’s biomechanics lab at the University of California, Riverside, gave an interesting talk on how different anole ecomorphs use their limbs. We characterize Anolis species by the portion of the habitat they use (e.g. twig/bush, trunk-ground). Species of the different ecomorphs often show stark differences in external morphology and behavior, which have evolved to match the microhabitat they use. Foster hypothesized that those differences in morphologies may lead to differences in locomotor kinematics.
Foster used high-speed video cameras to record lizards running on surfaces of different diameter and inclination, and digitized forelimb and hind limb joints in all the trials. She compared the limb movements of six Puerto Rican Anolis species, using two species from each of the grass-bush, trunk-ground, and trunk-crown ecomorphs. Using multivariate analyses, she found three major results: All ecomorphs used a similar strategy of modulating their hind limbs differently than their forelimbs when moving on the different inclines. Interestingly, when comparing ecomorphs, Foster showed that grass-bush species used both their forelimbs and their hindlimbs differently than the other ecomorphs. Furthermore, the two species within the grass-bush ecomorph use their forelimbs differently than each other.
Check out some of Kathleen’s other projects on her website.
How does the environment an organism experiences during development influence its phenotype, and does the development environment prepare the organism for success in its habitat? Corey Cates, now a Ph.D. student in the Warner Lab at Auburn University, used Anolis lizards to answer this question at the SICB meeting in Portland, Oregon.
Because anoles do not practice parental care, once a female lays an egg, the embryo is at the mercy of the environment. Soil conditions, such as moisture and temperature, will influence how the embryo develops, and can have lasting impacts on that organism’s phenotype. Furthermore, a lizard is expected to have highest fitness when its phenotype matches its environment. Cates designed an experiment that manipulated the development environment, and examined the desiccation performance and survival of hatchlings, following them into adulthood. Anolis sagrei that hatched from eggs left in dry, poor-quality soil experienced lower desiccation rates than those from eggs in moist, high-quality soil. Building upon previously-presented work, Cates showed that adult desiccation tolerance was not heritable. After following adult lizards from each treatment released into both high and low-quality habitats for more than a year, Cates found that desiccation trends persisted, and that organisms from dry incubation conditions performed better in dry habitats than those incubated in more favorable conditions. This study is a fascinating look into how anoles may handle changing climates in the future.
Matt explains his methods.
The winner of this year’s Division of Ecology and Evolution Huey Award, Matt McElroy, gave an interesting presentation on gene flow and the Bogert Effect in Anolis cristatellus in Puerto Rico. Roughly, the Bogert effect says that thermoregulatory behaviors may shield a species from selection pressures on physiological processes experienced in different thermal environments. Therefore, divergent selection is expected to be weak in thermoregulating species, which can adjust their behavior to maintain a consistent body temperature in a range of thermal habitats. Alternatively, thermoconformers’ body temperatures match that of the environment, and so face strong divergent selection when exposed to new thermal habitats. Gene flow is expected to be high across thermal gradients for the thermoregulators and low for the thermoconformers.
Matt investigated the phylogeographic population structure and gene flow in A. cristatellus on the island of Puerto Rico, discovering three distinct populations. The southwestern population, in the arid rain shadow, was most divergent from the other two. He also conducted trasects up the mountain (a decreasing temperature gradient), finding that genes were moving out of the arid zones, but not the other way. If the Bogert effect held true, we would expect gene flow in both directions in this thermoregulating species; perhaps there is strong selection on cool adapted genotypes in warm habitats, but not vice versa. Matt suggested that higher population densities in lower elevations may influence the uni-directional flow, or that habitat destruction (e.g. hurricanes, agriculture) creates open, sunny patches, allowing the low-elevation populations (warm-adapted) to exploit elevations that they would not have been able to otherwise.
Lauren Davis presenting her work on invasion success in lizards.
As our planet becomes increasingly connected and humans facilitate novel species interactions, we must ask why some introduced species are destructive and others relatively harmless. Lauren Davis, a senior in Dr. Michele Johnson’s lab at Trinity University, conducted a study on behaviors, and their neural correlates, that may influence the invasiveness of non-native lizards. She compared the invasive Anolis sagrei to the native Anolis carolinensis, the invasive House Gecko (Hemidactylus turcicus), and the native Texas Banded Gecko (Coleonux brevis). They hypothesized that highly invasive species display more ‘bold’ behaviors (in this case, the number of enclosure boundaries crossed during an experimental period) and have larger and/or denser neurons in associated brain regions than less invasive species. While there are many documented behavioral trials with boldness in Anolis, geckos have received little attention in this regard. Lauren and her fellow researchers found that A. sagrei is indeed bolder than A. carolinensis, but that the two gecko species do not differ in traits associated with the boldness syndrome (Fig. 1).
Figure 1: Invasive Brown Anoles are bolder than native Green Anoles
The researchers also found that neuron size in brain regions known to influence boldness and aggression were opposite than expected values, so the team plans to analyze neuron density in these regions to help explain the observed behaviors. This is one of the first studies comparing behavior and brain morphology to invasion success, and it paves an exciting path towards our understanding of species interactions in our changing world.
Lauren is graduating in May, and hopes to work in conservation or public health before continuing her education in graduate school.
My recently published paper in Herpetological Conservation and Biology about the effects of human land use on Anolis carolinensis (abstract below) came from an exciting season of field research. The summer of 2010 in Palmetto State Park in Gonzales, Texas was my first field research experience, where I took my first steps of many (little did I know) into the world of Anole biology. I worked under the supervision of Michele Johnson with an awesome lab group: Tara Whittle (our lab technician), Alisa Dill, Michelle Sparks, and Chelsea Stehle. Yes, I was the only male, and yes, that means I did get a tent all to myself. I took so many things from this experience, both scientific and not, that started my future as a field biologist.
We spent our days out in the hot Texas summer heat, catching, measuring, and observing our new friends, the green anoles. Each of us had our own research to work on that focused on various aspects of green anoles, and so we divided up our field time amongst our projects, helping each other collect data. We designated plots throughout the state park so we could compare the anoles in those plots. I studied the ways that human land use, such as clearing land for buildings, or constructing trails through natural habitat, impacts the lizards’ prey and the lizards themselves. While we did not find any clear trends showing that human disturbance impacts insects, which in turn affects the anoles, we were able to show that human-disturbed plots had higher insect biomass. This would seem beneficial to the anoles, who would theoretically have higher body condition (BMIs: SVL divided by mass) because of the greater amount of available food. However, we found that lizards (females in this case) in plots with greater levels of disturbance had lower BMIs.
The non-straightforward results from my study reflect the complexity of the relationship between humans and the environment; our impacts on the world do not always easily appear. I am taking what I have learned from this experience and am continuing to use anoles as a system to study human impacts on the environment at a local scale. This fall, I will attend the University of Rhode Island and study anoles with Jason Kolbe.
Abstract:
ANDREW C. BATTLES, TARA K.WHITTLE, CHELSEA M. STEHLE, AND MICHELE A. JOHNSON
Abstract.—Lizards frequently occur in disturbed habitats, yet the impacts of human activity on lizard biology remain understudied. Here, we examined the effects of land use on the body condition of Green Anole lizards (Anolisvcarolinensis) and the availability of their arthropod prey. Because human activity generally alters abiotic and biotic habitat features, we predicted that areas modified by humans would differ from areas with natural, intact vegetation in arthropod abundance and biomass. In addition, because biological communities in high use areas are often relatively homogenized, we predicted that higher human land use would result in lower prey diversity. Regardless of land use, we also predicted that areas with greater prey availability and diversity would support lizards with higher body condition. We studied anoles in six plots with varying levels of human modification in Palmetto State Park in Gonzales County, Texas. We quantified arthropod abundance, biomass, and diversity in each plot via transects and insect traps. We also determined lizard body condition using mass:length ratios and residuals, fat pad mass, and liver lipid content. We found that, although arthropod abundance did not differ across plots, arthropod biomass was higher in natural than in disturbed plots. Diversity indices showed that the plots varied in their arthropod community diversity, but not in relation to disturbance. Female (but not male) lizard body condition differed across plots, with body condition higher in natural plots than disturbed plots. Together, these results suggest that land use is associated with lizard body condition, but not through a direct relationship with prey availability.