All posts by Chris Thawley

JMIH 2017: Anole Morphology Round-up: Comparing Gecko and Anole Toepads and Patterns of Embryonic Limb Development in Diverse Lizards

Travis in the Dominican Republic with Anolis fowleri. Photo by Luke Mahler.

Travis in the Dominican Republic with Anolis fowleri. Photo by Luke Mahler.

Two recent talks at JMIH 2017 shed light on key morphological characters in anoles: toe pad shape and limb length. Travis Hagey presented his work which looks to shed light on why lizard toe pads are shaped the way that they are and addresses whether gecko and anole toe pads are convergent structures. Working with a team of undergraduates, Travis used geometric morphometrics to analyze the structure of toepads in a diverse group of geckos and anoles. Travis found that anole and gecko toe pads have a similar range of values for traits such as the placement of pads on the toes and the shape of the toes (skinny or fat) in relation to claws. However, anole toe pads formed a distinct cluster indicating that they occupy a unique area of trait space not used by geckos. This finding suggests that the divergent evolutionary history of anoles and geckos has resulted in independent evolutionary explorations of toe pad shape.

Immediately following Travis’ talk, Robin Andrews presented work investigating the embryological development of morphological characters in diverse lizard species. In anoles, consistent differences in the morphology of divergent species support the existence of different anole ecomorphs.  Previous research by Sanger and colleagues has shown that the differences in limb-length between anoles of different ecomorphs have their origins early in embryonic development. These early differences in limb length continue throughout the development of anoles into hatchlings and adult forms, a pattern known as transpositional allometry.

Robin compared patterns of limb, tail, and head growth in early stage embryos of four different lizard species, including a chameleon, two geckos, and the brown anole (Anolis sagrei). She found that species-specific differences in limb and tail lengths were exhibited as soon as limb and tail buds emerged from the body and were both best characterized by the same pattern, transpositional allometry. Embryonic head growth, however, showed no specific pattern. Robin’s findings suggest that the adaptive evolution of adult morphology in anole ecomorphs as well as other diverse lizard species is underpinned by developmental reprogramming.

Travis Hagey, Jordan Garcia, Oacia Fair, Nikki Cavalieri, and Barb Lundrigan: Variation in Lizard Adhesive Toe Pad Shape
Robin Andrews: Developmental Origin of Limb Size Variation in Lizards

JMIH 2017: Removal of Curly-tailed Lizards Increases Survival of Urban Brown Anoles

CRodriguez_JMIH2017

Interspecific Interactions Between Two Species of Invasive Lizards in an Urban Environment; Camila Rodriguez-Barbosa and Steve Johnson

An extensive body of work has addressed the eco-evolutionary impacts of the Northern Curly-tailed Lizard (Leiocephalus carinatus) on Brown Anoles (Anolis sagrei) (much of it receiving coverage right here, here, and here on Anole Annals!). These species co-occur not only on many Caribbean islands where much of this research has taken place, but also within the urban matrix of southern Florida, where both species are introduced.

Camila Rodriguez-Barbosa and Steve Johnson investigated the impacts of curlies on brown anoles in shopping centers in southern Florida where both species were plentiful. Camila first collected baseline data on anole and curly populations at eight sites before embarking on a quest to eliminate curlies from four of her sites. Over the next four months, she removed over 300 (!) curlies from these sites, many of which had brown anole remains in their stomachs.

She found that this removal had serious consequences for brown anoles. Compared to anoles from shopping centers where curlies were unchanged, A. sagrei at removal sites experienced higher survival and consequently greater abundances. These anoles also shifted to lower perches once curlies were removed, mirroring results from previous work which show that the introduction of curlies leads to brown anoles occupying higher perches to escape this dangerous predator. Camila’s work suggests that brown anole/curly-tailed lizard interactions may be similar even in very different habitats and provides a fascinating look at lizard life (and death) in the urban sprawl of southern Florida.

JMIH 2017: Brown Anole Reproductive Output Varies Seasonally

TMitchell_JMIH2017

Tim Mitchell, Josh Hall, and Daniel Warner: Seasonal Shifts in Anolis sagrei Reproduction Invoke Challenges for Scientific Reproducibility

Sometimes a scientist just needs hundreds of hatchling anoles for an experiment. Tim Mitchell found himself in this position recently, and, like a good lizard ecologist, he started breeding colonies of anoles in the lab to produce eggs to incubate until hatching. As he created three different breeding colonies from brown anoles (Anolis sagrei) in central Florida, one each in February, June, and September, Tim found that he had also created an ideal situation in which to examine how the reproductive condition and output of brown anoles varies across the breeding season.

Tim, along with his coauthors Josh Hall and Dan Warner, found that females produced eggs with significantly greater mass later in the breeding season. These eggs took longer to produce than those earlier in the year (a greater interclutch interval), and the eggs resulted in hatchlings that had higher mass in relation to the weight of their eggs. These reproductive differences remained even after accounting for the fact that female anoles were also larger and heavier later in the year.

These findings suggest that female A. sagrei may shift their reproductive effort from producing a higher quantity of eggs (i.e., more, smaller eggs resulting in smaller hatchlings) in the beginning of the breeding season, to producing higher quality eggs (i.e., fewer, larger eggs resulting in larger offspring) later in the breeding season. Tim’s findings also stress the importance of investigating and accounting for seasonal differences when examining reproductive output in lizards.

 

SICB 2017: Homeward Bound: An Incredible Anole Journey

(c) OwenMartin12, some rights reserved (CC BY-NC)

(c) OwenMartin12, some rights reserved (CC BY-NC)

The abilities of certain animals to navigate and home on a specific location over long distances are some of the most fascinating behaviors that scientists study. However, studying homing behavior, especially experimentally, can be a major challenge, as many animals home over long distances (thousands of miles), in difficult-to-study environments (underwater, high in the sky), on in ways that are technically difficult or very expensive to monitor. As we know, anoles can be relatively simple (and cheap!) to study. So what if anoles could be developed as a model system for studying homing behavior?

On the surface, the presence of homing behavior in anoles might seem unlikely, as many species are highly territorial and may not travel long distances during their lifetimes. David Steinberg and Manuel Leal showed that, while seeming unlikely at first glance, at least one species of anole, Anolis gundlachi, does indeed show strong homing behavior.

Anolis gundlachi, the yellow-chinned anole, is a denizen of cool, closed forests in Puerto Rico. Because these lizards stick close to their small territories, they likely have little specific knowledge of their surrounding habitats, potentially making navigation through unfamiliar areas difficult. Steinberg displaced anoles 40 and 80 meters from their home territories and then monitored their territories to see how many anoles returned. Surprisingly, 40-60% of females returned and 80% of males returned, even when taken 80 meters from their homes. Simulations of these movements show that it is highly unlikely anoles would be able to return to their territories in this way via random searching. Steinberg then tested whether two common mechanisms that support homing, use of magnet fields and visual detection of polarized light, were responsible for homing, but found that the homing abilities of these anoles do not depend on either of these two senses.

Finally, Steinberg tracked anoles through the Puerto Rican forest using radio transmitters, and found that anoles returned to their home territories with a high degree of accuracy, in some cases making a beeline home within 24 hours! These results suggest that homing ability may be more common in anoles than has previously been considered, and that strong selection for territory ownership in anoles may support spatial memory and navigation in these animals.

SICB 2017: Measuring the Immune System of Anoles

Caty Tylan measuring anole footpad thickness as a indicator of immune function.

Caty Tylan measuring anole footpad thickness as a indicator of immune function.

A major challenge for organisms is to protect themselves from pathogens, things in the environment, including other organisms or toxins, that can cause disease and harm them. Animals, including anoles, have several different types of immune responses by which they can respond to pathogens. Ecologists are particularly interested in how these immune responses work in natural settings, how effective they are at protecting organisms, and how other aspects of an organism’s environment, including diet, stress, and reproduction, may positively or negatively impact immunity. However, immune systems are very complex, and measuring immune function, especially in the field, can be quite challenging!

Ecoimmunologists have developed various procedures to test different aspects of immune function, but ideally these procedures should be validated, or proved to be meaningful, in each organism they are used in. The phytohemagglutinin (PHA) skin test is one such assessment of immune function that is commonly used. This procedure involves injecting a small amount of phytohemagglutinin, a plant protein that provokes an immune response in animals, into the tissue of an organism of interest, waiting a given amount of time, and measuring the resulting swelling which is then used as an index of immune response. Researchers like this test because it is minimally invasive, works in almost any species, and is simple and easy to do in the field. Though this test has been used in multiple reptile species, it has never been validated in a reptile.

Enter Caty Tylan, a Ph.D. student and diploma-carry veterinarian from Penn State University, who addressed this issue in her talk “Local and systemic immune response to phytohemagglutinin: Validation of the PHA skin test in the green anole, Anolis carolinensis.” Caty chose to validate this test in green anoles (Anolis carolinensis), a model anole species, using two different types of PHA, PHA-L and PHA-P, which are available to researchers. She injected PHA into anole footpads and compared swelling in those feet over 48 hours post-injection. By comparing swelling in these feet to those which were only injected with sterile saline, Caty showed that PHA does induce a swelling response over 48 hrs, and that this response is the same for both types of PHA. She also examined the white blood cell counts in these anoles and found that PHA-L, a more purified and specific PHA, induced the stronger lymphocyte response, an immune measure that many ecoimmunologists look to quantify. In the future, Caty will examine histological sections of injected anole feet to examine the local immune response to PHA injections and fully validate this assay. This work should allow effective use of the PHA assay in future anole research and support investigations into how various environmental variables affect cell-mediated immune function in reptiles.

JMIH 2016: Evolution Isn’t Slow–Experimental Studies of Eco-Evolutionary Dynamics

For many years, biologists believed that evolution was a process that played out over vast stretches of geological time and would not be observable during field studies. More recent research, however, has begun to show that evolution can occur very quickly and that experiments in the field can address evolution in action. Tom Schoener, eminent professor at the University of California, Davis, shed light on our evolving view of how evolution occurs in his talk, “Eco-evolutionary Aspects of the Lizard Anolis sagrei in an Island Metapopulation” at JMIH 2016.

By introducing a novel predator, the curly-tailed lizard (Leiocephalus carinatus), which devours anoles, to a series of small islands in the Bahamas, Schoener and colleagues were able to observe evolutionary responses in A. sagrei in fewer than 10 years. By preying on A. sagrei, curly-tailed lizards induced behavioral changes in perch height, and created selection for relatively longer limbs that increase anoles’ ability to escape this predator. Curly-tailed lizards also caused a variety of ecological effects, including reducing anole populations and changing arthropod abundance, which may affect the future evolution of anoles on these islands. Ongoing monitoring shows that these anole populations seem to be rebounding and that different types of selection may be acting on hindlimb length.

A curly-tailed lizard (Leiocephalus carinatus) displays its namesake in Florida. Photo: Ianaré Sévi.

A curly-tailed lizard (Leiocephalus carinatus) displays its namesake in Florida. Photo by Ianaré Sévi.

Perhaps not surprisingly, many of the experimental islands were occasionally devastated by hurricanes which are becoming more frequent and more powerful in the Caribbean. While these extreme weather events interrupted some of Schoener’s planned research, they also provided a unique opportunity to study how hurricanes may cause natural selection. Schoener found that anoles which survived hurricanes had longer hindlimbs, and these lizards were better able to hold onto trees and other perches at high wind speeds, likely increasing survival of hurricanes by preventing lizards being blown out to sea! Taken together this body of research suggests that novel environmental changes, such as invasive species or increasingly extreme weather, exert selection on organisms and that we can observe these organisms evolving rapidly on ecological timescales.