I am happy to report that the “uninvaded” team has returned to PA, lizards in hand–or bag as it were. Our team, consisting of Braulio, Caty, and myself, traveled to Tennessee and Arkansas. Arkansas prides itself on being “The Natural State” for its “natural scenic beauty, clear lakes and streams, and abundant wildlife.” I can’t speak to most of that, but it does have lizards!
Fence lizard with a regenerating tail.
Rainy and overcast days slowed us down a bit. As ectotherms, lizards rely on external sources of heat, which means they like to bask in sunny spots in order to warm up. The thick clouds didn’t provide many good basking opportunities, but thankfully a few lizards made an appearance in the brief moments of sun.
Sometimes fence lizards like rocky habitat.
Many other lizards like to bask on trees.
We did see a few sunny days, which gave Braulio and Caty the opportunity to catch their first lizards.
Braulio with a Tennessee lizard.
One of Caty’s first catches!
Lizard selfies are the best selfies.
We even managed some “expert” catches, on more than one occasion slowly driving by a basking lizard and noosing it through the open car window.
Because we were looking for females, we of course became experts at catching males. One male lizard really hoped I was a tree. We tried to return him to his log, but on two separate occasions he ran up my leg. Sorry little guy!
Nope, not a tree.
Another male, pictured below, really surprised me. Lizards vary in coloration, but not usually by much. I’ve never seen a fence lizard so dark!
A very dark fence lizard. His chest badges were impressive as well!
After two weeks of catching, we headed back to the lab. Our females are now happily housed in their nesting boxes, and one has laid her first clutch of the season. We’re all excited to see the resulting hatchlings!
Check back soon for more stories and photos from the field as well as updates on the specific research projects happening this summer.
Hello, my name is Dustin Owen and I’m one of three new PhD students in Tracy Langkilde’s Lab. I’m originally from east-central Indiana where I got my B.S degree in Biology from Ball State University. While there I was able to work on a lot of different questions on a lot of different organisms. My first research project was on the allometry of shell morphology in a freshwater snail,Elimia livescens, in Dr. Mark Pyron‘s Lab. After that I worked on several other projects including looking at hydrology and freshwater drum (Aplodinotus grunniens) with Dr. Pyron, artificial scent and small mammal trapping and various bat projects with Dr. Timothy Carter, and even my own independent research project on how roads impact the stress physiology of copperheads (Agkistrodon contortrix).
Copperhead (Agkistrodon contortrix) on a gravel road.
After my undergrad, I went to Austin Peay State University and continued my interest in stress physiology and reptiles. While there, I studied stress physiology in several species of snakes.
Racer (Coluber constrictor) Selfie
Now that I’m here at Penn State I plan on continuing my interest in stress physiology, using the invasive Fire Ant (Solenopsis invicta) and Eastern Fence Lizard (Sceloporus undulatus). While I have never directly studied Fence Lizards in the past, I have assisted expert Fence Lizard catcher Kris Wild on his Master’s Thesis work on fire and Fence Lizards. Now, armed with my new Kris Wild custom lizard noose, “The Pub Maker”, I’m ready to lay siege to some fence lizards in the name of science!
In my spare time I enjoy being outside, football, basketball, and hanging out with my girlfriend Heather. I also enjoy exploring with my niece Lilly. Teaching her about biology (she’s especially interested in bats and snakes) has been one of the greatest joys in my life. One day, she’ll be a far greater biologist than I’ll ever be, but until then I’m happy just taking her outside and watching her learn about nature.
Me with a juvenile Common Water Snake (Nerodia sipedon) and Lilly with a Ring-necked Snake (Diadophis punctatus).
This semester, being my fourth semester working within the lab, I like to think I have heard about all the research that’s been going on in one way or another. I had previously finished working with Bradley Carson last Spring semester on tadpole analysis and was eager to delve into something new. Dr. Langkilde got me in touch with Gail and we quickly met to discuss more work for the next 14 or so weeks. Taking 19 credits this semester and getting ready to apply to medical school rendered me nearly unavailable during the week. Gail of course knew the feeling and set me up on something I could do on my own time, at my own pace. This something was a project I had not heard of within the lab, and this excited me. When I went to meet she immediately brought up about 7 or so videos of lizards. The set up looked something along the lines of this.
When I saw this I immediately asked myself a few questions. First, why are there so many lizards in this video? And second, what’s that huge log in the middle of their bins? Gail started to explain her research to me and answered these questions. She was observing the lizards’ behavior over a short period of time within these bins to see how they would react to different hormone treatments. This experiment allows us to see if treatment with stress hormones (corticosterone), sex steroids (testosterone), or both have lasting effects on behavior–like aggression. She also let me know that huge thing in the middle of the bins is just a small shelter. I have been spending my time watching these lizards show all different types of behaviors. I see some lizards spend 10 minutes running circles around their bins and other lizards so lazy I have to zoom in on their stomachs to check if they’re actually breathing! Some of the lizards aren’t very social.
While others seem to be good friends with one another.
Nonetheless, these videos have occupied much of my time and have continued to keep me interested. I look forward to see what Gail does with all the behavior charts I have filled out for her and am eager to help her with the next step in this experiment.
(Ed. note: Hopefully this helps us explain how hormones affect behavior. Maybe lizards dosed with testosterone are more aggressive? Maybe stressed out lizards are more solitary? Stay tuned for the results!)
While on a quick Spring Break trip, I needed to get a herp fix since I’ve been stranded in a land of ice and snow (errr, State College) for the past four months. Alabama to the rescue. While I mostly just hiked in the glorious (to me) 65-70 degree weather (and did manage to actually get a sunburn on my pasty white arms), I did see some herps along the way, whether by flipping a random rock and log or just stumbling across the odd lizard. Here are some quick pics to tide you over the next month or two until spring unleashes warm enough weather for the herps to come out in force a little farther north.
My first fence lizard of the year! This lady was quite cold but basking at the base of a tree trying to get a jump on her activity season.
After quickly catching the fence lizard (hands only…how a real lizard ninja does it!) I contemplate just how the heck I’ll set up my projects this summer.
Fire ants were still active as well, although they needed a little motivation (errr, an attacking stick) to get them to show themselves in the cooler weather.
A seal salamander (Desmognathus monticola) works on its tan streamside in the mountains of northern Georgia.
Another desmog takes a peek out of the stream to cast a wary eye at the bumbling human who just pulled a rock away from its burrow mouth (I put the rock safely back).
A marbled salamander (Ambystoma opacum) squints its eyes in the bright light after being found underneath a log in southern Alabama.
Welp, that’s all for now! Hopefully a panoply of critters will be out here in PA soon enough, and we’ll be rolling in fence lizards (and hopefully not fire ants!) in the near future.
To get away from fire ants of course! Fence lizards, like most organisms, generally prefer to avoid being messily devoured by predators, and, to elude predators, animals employ a variety of defensive strategies. Animals may hide, flee, avoid detection (by camouflage or other means), be poisonous, pretend to be poisonous, have armor, and even preemptively attack a predator. For example, the Eastern Hognose Snake (Heterodon platyrhinos) employs a truly astounding suite of defensive strategies, including: puffing itself up to look bigger and more like a venomous snake (hence their nickname, the “spreading adder”), striking with a closed mouth, vomiting, and defecating to make itself as gross/distasteful as possible, vibrating its tail to mimic a rattlesnake, and playing dead by turning over on its back and sticking out its tongue.
A hognose snake feigns death (thanatosis) as a defensive strategy. Photo credit: Douglas Mills.
Fence lizards have defensive strategies too. Research in our lab has shown that one of the main ways that fence lizards adapt to fire ants is by fleeing from ants more frequently. Fence lizards from areas without fire ants will only flee from fire ant attacks about 50% of the time; the other half of the time, they freeze and remain motionless, and the lizards would likely die if we did not remove the ants and allow them to recover. However, when we study fence lizards from areas with fire ants, we notice that up to 95% of lizards flee when attacked by fire ants, a much higher percentage. This strategy is very effective, since fire ants can only prey on adult fence lizards when they can recruit to attack in large numbers.
However, in our lab meetings we began to wonder: why do fence lizards from areas without fire ants freeze so much of the time? It seems most likely that lizards from areas without fire ants freeze when attacked because this is an effective, adapted defensive strategy against native predators. In other words, just as fire ants have put pressure on fence lizard populations to adapt (in this case, by running away more often), native predators have put pressure on fence lizards to freeze (about half the time, at least). While not running away from a predator when given the chance may seem like a bad strategy, this approach makes more sense when we consider what the native predators of fence lizards are. They include many types of predatory birds, such as hawks and falcons, as well as several snake species, including black racers (Coluber constrictor) and coachwhips (Masticophis flagellum) among others. These predators are primarily visual hunters and also very speedy. A fence lizard in danger from one of these predators would have little chance of outrunning it, unless a refuge were near at hand (or claw); however, as fence lizards have excellently camouflaged patterning, freezing could be a very effective strategy, as the bird or snake might, like the erroneousT-rex in Jurassic Park, have a difficult time seeing the fence lizard if it remained motionless.
After these discussions, I, along with two undergraduate researchers, Shannen McGinley and Elexa Baron, decided to test whether fence lizards from different areas (those with fire ants and those without), would react differently to a simulated predator attack. To conduct these tests, we first needed a predator; after some quick research, I discovered that a common avian predator of fence lizards is the American Kestrel, a smaller falcon that preys on many species of lizards. The Penn State University Bird Collection happened to have a preserved kestrel salvaged from a car strike that they were kind enough to lend us. After naming our kestrel “Cadfan”, I proceeded to get him ready for his close-up: I braced his wings into a half spread position, as if he were swooping in for a strike; built him a wire harness, to allow us to hang and swing him from the ceiling in a simulated attack; and gave him a pair of really intense eyes (as we know from personal experience that fence lizards will respond to large eyes and being stared at).
Cadfan and me chilling in the lab. Note his intense and intimidating gaze.
Next, we needed to design an arena in which to conduct behavioral trials. We set up a small arena in the middle of an animal room that contained a tub identical to those our lab lizards live in, and we lined it with sand and put in a half log, a type of lizard shelter. To allow us to simulate a kestrel attack, we hung Cadfan from the ceiling of the animal room using fishing line. We also built a blind for Cadfan and for ourselves, to prevent the lizard from seeing either the kestrel or the humans. As part of the construction, we built a webcam into our blind to allow us to observe and record all the trials for later analysis.
Left: Cadfan hanging over the arena showing how close he can swoop to the lizard perch. Right: The backside of our blind, with datasheets, laptop, and webcam set up to allow data collection.
After finally getting the room set up to our exacting specifications, we were ready to run trials with our lizards. Conducting a trial required two people. One person stayed behind the blind and held Cadfan up and out of view of the lizard. The other person fetched a random lizard from its housing and walked it quickly to the trial room, where we took it’s body temperature and set it on the log perch in the middle of the arena. That second person, the lizard-getter, then walked behind the blind, starting recording with the webcam, and gave a big thumbs-up signal to the bird-holder. The bird-holder simultaneously released Cadfan, and also turned on a small lightbulb that could be seen in the webcam but not by the lizard (this allowed accurate timing of the trial). We let Cadfan make four swoops over the head of the lizard and then returned the lizard to its housing, while recording if the lizard reacted to the simulated attack and how long it took to react. We also classified how strong any reaction was; some lizards just ducked their heads or shifted to the side, much as you or I might if a large insect flew at our heads. Other lizards reacted much more strongly and dove into the sand or underneath the log shelter. See below for a video showing our setup and a couple of trials!
We’re still analyzing the data from these trials now, but, to the naked eye, we haven’t seen a large difference in responses to the bird predator based on where the fence lizards come from as we’ve seen in response to fire ant attacks. This could mean that lizards might be able to distinguish between different types of predation threats or that something else is going on. We’ll post again when we publish a paper on our trials, so keep an eye out for those results here (and any attacking kestrels that might be nearby)!
The best way for scientists to share their research is to publish it in scientific journals. This can be a lengthy process, so it’s always very exciting when your work is finally published. We’re so excited that we wanted to share some of our recent publications with you. Click the links below for the abstract (or to download the paper if you’re a fancy pants scientist/academic with access!)
No evidence of selection by predators on tadpole boldness. Bradley E Carlson and Tracy Langkilde. Behaviour
Read more about this on our blog here.
Tadpoles!
Latitudinal and seasonal variation in reproductive effort of the eastern fence lizard (Sceloporus undulatus).
Wei-Guo Du, Travis R Robbins, Daniel A Warner, Tracy Langkilde, Richard Shine. Integrative Zoology
Rise and Fall of a Hybrid Zone: Implications for the Roles of Aggression, Mate Choice, and Secondary Succession. Travis R Robbins, Lorelei E Walker, Kelvin D Gorospe, Stephen A Karl, Aaron W Schrey, Earl D McCoy, Henry R Mushinsky. The Journal of Heredity
On the incidences of cannibalism in the lizard genus Sceloporus: updates, hypotheses, and the first case of siblicide Travis R. Robbins, Aaron Schrey, Shannen McGinley, Aaron Jacobs. Herpetology Notes
Read about this on our blog here.
A cannibalized Sceloporus undulatus lizard (right fecal pellet) and one of his siblings (left).
Bearded ladies: females suffer fitness consequences when bearing male traits.
Lindsey Swierk and Tracy Langkilde. Biology Letters.
More about this one on our recent blog post here.
A male (left) and female (right) fence lizard. The female is a “bearded lady” with pale blue badges.
We’ve also had a whole bunch geographic distribution notes published in the journal, Herpetological Review. That usually means we observed a species outside of its known range. We had four notes in September’s Issue and seven in December’s issue. Authors from our lab included Chris, Brad, Gail, Sean (lab alum), and undergrads Mark Herr, Mark Goldy-Brown, and former intern Jennie Williams. Pretty cool!
Over the past several years, I like to think I’ve been a sort-of successful spy on the secret lives of herps. As a behavioral ecologist with a focus on reproductive behavior, invading animal privacy comes as part of the job. Thankfully for my conscience, my subjects don’t seem to mind… or really even notice. One of the plus sides of working on reproductive behavior is that— at least when sex is in the offing—animal subjects seem to care a lot less that big, lumbering, non-predatory researchers are nearby. In this post, I’d like to share with you the delightfully graphic details of one of my spying expeditions on eastern fence lizard (Sceloporus undulatus) sexual competition.
Males of all species tend to fight. A lot. Not exactly a ground-breaking revelation. (Females fight too, but generalizing over all species… let’s face it: males on average tend to fight more.) What is immediately apparent across the animal kingdom is that fighting with males of your same species can be very, very costly. Think about some examples of “classic” male weaponry – antlers, teeth, tusks, horns – they’ve evolved to wound, maim, injure, and even kill.
Figure 1. Male on male combat occurs in many species including serious battles between male southern elephant seals (Mirounga leonina) which use their teeth to gash competitors (Top) and elk which spar with their antlers (Bottom). Images from Wikimedia
Fence lizard males—despite their modest size, lack of obvious weaponry, and generally sweet nature (a spy’s personal opinion)—also can be absurdly aggressive when it comes to sex. Quick natural history lesson: Male fence lizards defend home ranges that abut or overlap those of other males; females have smaller home ranges that are nestled inside one or more male home ranges. When males fight with each other, it’s often over access to females who, from the males’ perspective, wander too much. Females watch males fighting and may make their own mate choice decisions based on what they see. So, you might imagine that it would behoove males to give each fight their all, not only to win the right to the lady, but also to impress her. However, that’s not what we’ve observed. Instead, we see a wide variation in fighting strategies: some male lizards are downright timid, backing down pretty quickly, while others go right for the throat, so to speak.
Above: A bout of territorial competition between two Sceloporus (either graciosus or occidentalis) involving chases and whole-body shudders.
As part of our research, we staged encounters between males to figure out why so much variation exists in how and when males escalate fights. We placed males in a laboratory arena, separated from each other (and a tempting, lovely, lady lizard) by clear glass to prevent any real bloodshed between competing males. Instead of observing who the winners and losers of real, pitched lizard battles were, we used an excellent indicator of contest escalation—display behavior. Display behaviors are body postures and movements that convey messages to competitors, for instance, lizard “pushups” and whole-body shuddering that are signals of territory assertion. Using video recordings, we carefully documented every display behavior each male sent to his competitor—essentially transcribing a non-verbal dialogue between two increasingly angry males. We were able to “decode” this dialogue, assisted by information collected and previously published by other researchers around the world. And what we found after decoding these secret messages was pretty surprising.
Figure 2. A diagram of the arena used in trials of display behavior for Sceloporus. Males were placed in the two side areas and could view a centrally placed female and the other male through clear dividers.
Because fighting can be so costly (not only is fighting exhausting, but there’s a high risk of getting a serious bite), we initially guessed that differences in the tendency to escalate fights may exist because males that can afford to lose more (“big and strong” males) were more willing to take the chance of having a costly encounter than scrawnier males. What we observed, however, was almost the exact opposite. Of the two males in each trial, we found that the wimpier of the two consistently responded to his competitor’s display behavior with more aggressive behaviors. The really cool part about this is that the tendency to respond with aggression isn’t hardwired— it’s not that small males were always more aggressive, but instead that the males that were smaller than their competitors were more aggressive. A nuanced, but important, distinction. Put a medium sized male with a bigger competitor, and he’d act like a tough guy; put the same lizard with a tiny competitor, and he wouldn’t bother to give the challenger the time of day. So, it seems like fence lizard males are somehow assessing their own chances of success in a fight against every individual competitor that they face, and adjusting their strategies accordingly. Being willing to escalate a fight may be crazy risky, but also could literally be the only way to defeat a physically formidable opponent. Littler guys need to be willing to take the risk in order to reproduce. Bigger males are more chill: there may be no need to waste time and energy doing displays when they don’t need to, since they’ve really got the size advantage if the confrontation were to come to blows (or bites!).
Part 1 of 2 in the fence lizard fire ant saga: Rapid evolution of fence lizards (Sceloporus undulatus) in response to selective pressures imposed by red imported fire ants (Solenopsis invicta).
Dr. Travis R. Robbins is a postdoctoral research fellow in the Langkilde Lab who studies the ecological mechanisms that result in evolution. His interests range from the evolution of life histories in response to climate change to behavioral evolution in response to invasive species to the evolutionary significance of culture. Most of his research, however, is on Sceloporus lizards (AKA Spiny lizards or Swifts), focusing on their genetic and plastic responses to environmental change and the underlying interactions between physiological (e.g. hormonal), behavioral (e.g. resource use and niche construction), and epigenetic mechanisms. His research endeavors have brought him to Costa Rica, Panama, Mexico, the subtropics of Florida, and inside Biosphere 2 in the Arizona desert, but he is currently focusing on lizard evolution in the Southeastern US, which brings us to the current blog post.
Photo credit: T.R. Robbins
For the past three years I have been studying how fence lizards change their behavior and morphology after red imported fire ants invade the fence lizard habitat. This amazing study system that Dr. Tracy Langkilde fostered almost a decade ago reveals more exciting ecology with every research project! Tracy found an interesting trend across fence lizard populations that were invaded by fire ants at varying times in the past. The longer fence lizard populations coexist with fire ants, the more fence lizards in each population begin to respond to agonistic encounters with fire ants.
Change in use of (a, d) body twitch (solid symbols) and (b, e) flee (solid symbols) defensive behavior, and (c, f ) the relative hind limb length (shown as hind limb length/snout–vent length, SVL); of adult vs. juvenile fence lizards (Sceloporus undulatus) across sites with different histories of fire ant invasion. Open symbols represent behavior exhibited during control trials conducted in the absence of fire ants. Sexes are pooled for all panels. In all panels, values for adults represent mean 6 SE for 20 male and 20 female lizards from each site; values for juveniles represent mean 6 SE for 157 juveniles born to 16 females from Site 1, and 128 juveniles born to 18 females from Site 4. Figure – Langkilde 2009 Ecology 90(1): 208-217
Usually this lizard species uses crypsis to avoid predation, so it is not prone to moving when something, that is usually harmless (i.e. not a fire ant), crawls over it. The lizards respond to fire ants, however, by dancing (twitching) and running away! And they evolve longer hind limbs so they can be really efficient at it!
Most of our data collection has been about how fence lizards respond to fire ants when they find themselves being attacked on top of a fire ant mound. Fire ants are quite aggressive when they find someone knocking on their door. Unfortunately, especially for those of you that live with fire ants in your yard, fire ants spend a lot of time away from the mound ubiquitously foraging and roaming around the habitats they invade. Lizards surely encounter fire ants when they have the displeasure of accidentally knocking, but most of the time lizards are basking in the sun or foraging for food somewhere other than fire ant mounds. Thus, we wondered how often a fence lizard would encounter a fire ant away from a fire ant mound, so we conducted an experiment. We placed lizards 4 meters away from a fire ant mound (and fire ant mounds are approximately 10 meters apart where abundant, so this almost as far as you can get from one!) and observed them to measure how long it would take for a fire ant to find the lizard. We also measured the behavioral response of the lizard and its effectiveness in avoiding an attack.
We call the first fire ant to find a lizard a “scout”, and this single ant is not much of a threat to a fence lizard. However, that scout tells his buddies where to find the lizard, and a bunch of ants start heading toward the lizard to attack. We call this “recruitment”, and this higher number of ants attacking is potentially dangerous. It only takes 12 ants to immobilize an adult fence lizard in 60 seconds. But, don’t worry, we never let this happen during our trials. We hypothesized that fence lizards that grew up with fire ants would enact their dance and run technique (twitch and flee behavior) whereas naïve fence lizards would not. We also hypothesized that the dance and run would be effective at curtailing the recruitment. If fence lizards responded to the scout before the scout could bring back recruits, the recruits would come to an empty spot, and the lizard in its new spot would no longer be threatened by an attack.
Our results suggested that this was indeed the case! Experienced lizards (those caught in the field at the invaded site) danced and ran when they encountered the scout.
The proportion of field-caught (gray bars; n = 40 from each site) and laboratory-raised (white bars; n = 22 from each site) adult fence lizards from an invaded and uninvaded site that behaviorally responded to attack by red imported fire ants on a fire ant mound. Bars represent mean values ± 1 SE. Different letters above the bars denote significantly different groups. Figures – Freidenfelds et al 2012 Behav Ecol 23: 659-664
We found that experience with fire ants (lizards from the invaded site) affected only adults, however, because juvenile lizards from all populations were scaredy-cats, running away quickly. We also found that dancing and running in response to a scout was an effective strategy to escape the danger of an attack by recruits.
The proportion of fence lizards that had red imported fire antsrecruit to attack them after being located by a fire ant scout, comparing responder (lizards that behaviorally responded to fire ants, n = 13) and nonresponder (lizards that did not respond to fire ants, n = 7) adults. Bars represent mean values 6 1 SE. Different letters above the bars denote significantly different groups.
Our results suggest that when lizards grow up with fire ants they change their behavior in an adaptive way that likely increases their biological fitness by avoiding attacks by stinging fire ants (likely keeping them alive and in better moods). Overall, we have found that the longer a population has coexisted with fire ants, the more fence lizards in the population exhibit the changes, suggesting that these behaviors and morphologies are evolving to help fence lizards adapt to deal with the pesky, painful, and potentially portentous fire ants. We are currently examining whether or not these behaviors are inherited by comparing behaviors of mothers to their offspring once they become adults.
Many other lizards like to bask on trees.
A fence lizard on a fence. So satisfying.
The Lizard Log 