The Lizard Log

The Langkilde Lab in Action


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Sex-dependent effects of maternal stress in lizards

Check out the second chapter of Dustin’s thesis on the “Sex‐dependent effects of maternal stress: Stressed moms invest less in sons than daughters”!

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Multigenerational effects can have important and sex‐dependent effects on offspring. Sex allocation theory predicts that females should differentially invest in sons and daughters depending on sex‐specific fitness returns and costs of investment. Maternal stress‐relevant (glucocorticoid) hormones may be one mechanism driving this effect. We investigated how maternal stress hormones differentially affected sons and daughters by manipulating levels of the glucocorticoid, corticosterone (CORT), in gravid female eastern fence lizards (Sceloporus undulatus) and quantifying reproductive investment and sex ratio of resulting clutches, and the mass, snout‐vent length, and body condition of sons versus daughters at hatching. We found no effect of maternal CORT‐treatment on the number or size of eggs laid or on the sex ratio of resulting offspring, but sons of CORT‐treated mothers were shorter, lighter, and of poorer body condition at hatching than were sons of control mothers. We found no difference in size or condition of daughters with maternal treatment. Our results suggest that maternal stress, mediated by elevations in maternal CORT concentrations, can have sex‐specific effects on offspring manifesting as lower investment in sons.

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Word Clouds and Receptions

The end is near! I am happy to report that both Chris and I have submitted our final dissertations to the graduate school. What a relief!  Now that my dissertation is off to the printers, I decided to do some stats…

Unsurprisingly, the most used word in my dissertation (excluding common words), is “stress,” clocking in at a word count of 392 (out of 35K total words). Close behind were CORT (296), lizards (225), immune (201), and ants (144). Sounds about right! (The most used word was “of,” with a word count of 681. Fascinating!)

I couldn’t help but display this graphically, because who doesn’t love a word cloud?

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A word cloud featuring the most commonly used words in my dissertation. Note that “killing” applies to bacteria only! (Make your own at wordle.net)

For those of you keeping track, this is the “cleaned up” version–the original was quite overwhelming! I removed the citations and statistics as well as a number of prepositions,  less exciting words (“may” was a big one), and anything that occurred fewer than 20 times throughout my dissertation.

In other news, Tracy and I recently attended the 2016 Penn State Alumni Association Recognition Dinner, where I was presented with the Alumni Association Dissertation Award.

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Receiving the award. Thanks Penn State Alumni Association!

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Dave Eissenstat, head of the Ecology program, and Tracy helped celebrate at the recognition dinner.

The 13 graduate student winners were invited to talk about their research. I chose to highlight the last two chapters of my dissertation, which have been submitted to various journals. Here’s a sneak peak of the findings, as described in my short talk/acceptance speech:

My dissertation research addresses the circumstances under which stress produces negative consequences. Animals, including humans, have a way of dealing with stress, called the physiological stress response. This response involves a suite of changes in the body to help an animal deal with and recover from the stressor—these changes can mobilize energy and induce certain helpful behaviors to help deal with the stressor. Because of this stress response, experiencing a stressor isn’t always a “bad thing”.

That said, in order for these changes to occur, an animal temporarily pulls energy away from other systems that aren’t immediately important—like growth and reproduction. That means when stress is frequent, when it doesn’t go away, there can be negative consequences on these traits—on growth, reproduction, and immune function.

The immediate consequences of stress are fairly well studied, but we know less about how stress experienced during development or in previous generations can affect adult traits.

To investigate this, I took advantage of populations of eastern fence lizards that co-evolved with different levels of stress in the environment. Some populations co-occur with invasive fire ants, which bite and sting lizards. These encounters are stressful for the lizards, and if you’ve been stung by a fire ant, I’m sure you can relate. So this study system gives us a unique opportunity to look at populations that have long history—many generations—of high–stress and compare to populations that do not have history with this kind of stress.

My research reveals that ancestral history with stress is actually really important. If a lizard’s ancestors experienced high-stress, that affects how it responds to stress as an adult—regardless of its personal experience with stress within its lifetime. So it’s not what it went through, but what its ancestors went through, that determines how robustly it responds to stress.

But it turns out the combination of a lizard’s personal experience and its ancestors’ experience that determines the immune consequences of stress. Researchers don’t usually consider how stress in previous generations can affect physiology, but my research indicates this should not be overlooked

Understanding when stress will become beneficial and when it becomes harmful will allows us to better predict how animals will be affected by the increasing amounts of stress due to global change, and to better allocate resources to manage these effects.

I would like to thank the Penn State Ecology Program and my advisor, Tracy Langkilde, without whom I could not have completed my degree. I would also like to thank my boyfriend, Rich, for his support and the Alumni Association for the recognition. It is a privilege to have your support, and I am excited to join the thriving community of Penn State alumni. Thank you.

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Major thanks to my boyfriend, Rich, who supported me not only at the dinner, but throughout my graduate studies. You’re the best!

 


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Starting the year with a bang!

2015 ended in style for the Langkilde Lab, and we are proud to report that thus far 2016 has been just as exciting! In the last few months, we have celebrated a number of lab accomplishments and enjoyed some attention from the media. Here’s a taste of what we have been celebrating:

 

Press:

LangkildeLizard 2Penn State News featured the lab’s work on adaptation to invasive species and anthropogenic noise in this great article by Matt Swayne, complete with disco references. It’s definitely worth the read!

 

Tracy1Penn State Science recently covered the lab’s research on the effects of stress, our collaborations, and Tracy’s mentoring style. The story quotes many lab members and also includes a “person-to-person” feature on graduate student Gail McCormick.

 

 

Other achievements:

  • PI Tracy Langkilde recently accepted the position as the Head of the Department of Biology.
  • Gail McCormick successfully defended her PhD dissertation and won the Alumni Association Dissertation Award. This award is among the most prestigious available to Penn State graduate students and recognizes outstanding achievement in scholarship and professional accomplishment.
  • Chris Thawley won the Intercollege Graduate Student Outreach Award, a university-level award that recognizes outstanding achievements related to bringing scholarship to the community. Chris will be defending in February and will be starting a post-doc with the Kolbe Lab in May, where he will be investigating the effects of urban light on anoles.
  • Kirsty MacLeod will be joining the Langkilde and Sheriff Labs as a post doc this spring. We are excited to have her!
  • Michaleia Mead will be staying on as a Masters student with Chris Howey. They will be investigating the effects of prescribed burns on amphibians and vernal pools.
Hooray!

Hooray!

Stay tuned throughout 2016 for more exciting research and updates from the Langkilde Lab!


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Gearing up for SICB!

Happy New Year!

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New year, new beginnings. And hats. Lots of hats.

As we start to wrap up our holiday break, Chris T. and I are preparing for a trip to Portland, Oregon for the 2016 annual meeting of the Society for Integrative and Comparative Biology (SICB). We will both be presenting talks on Monday.

I will be expanding on results I presented at ESA in August, which address how stress (fire ants) experienced in early life or in previous generations affect adult physiology and immune function in lizards. My talk is Monday, January 4th at 11:15 in room B110/111.

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Chris will be sharing his results from SSAR with a new audience. He will discuss how invasive fire ants have reversed geographical patterns in fence lizard ecology, including their behavior, stress responses, and morphology, across their range in less than 75 years. Chris’s talk is also on Monday, January 4th at 11:30 in room B114. A determined Langkilde Lab follower could attend both talks back to back in nearby rooms! 🙂

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Come say hello if you will be there!


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What Makes Stress Stressful?

Stress is a familiar concept to most people. Paying the bills on time, entering a week of exams, caring for a sick loved one, or even sitting in heavy traffic on the way to work. When you get stressed out, your body goes through a series of changes to help you deal with that stress. This stress response includes both physiological and behavioral changes and is generally a good thing! For animals, the physiological stress response can mobilize energy and trigger important behavior, perhaps to get away from a predator. It can also enhance immune function in the short term to prepare for wounding or infection that might occur as a result of that stressful encounter.  Short term stress is typically called “acute,” and the resulting stress response is very similar across vertebrates—because it works!

Stressors come in a variety of forms.

Stressors come in a variety of forms.

If stress lasts for a long time, however, there can be costs to using so much energy on the stress response. If you have ever become sick after a week of exams or a particularly challenging week at work, you know what I’m talking about. Long term stress—typically called “chronic” stress—can suppress immune function as well as growth and reproduction.

Sometimes, however, these generalizations don’t hold up—short term acute stress may produce negative consequences or long term chronic stress may produce positive outcomes. This got us wondering—just what is it about stress that might lead to negative consequences? We discuss just that in our latest paper published in General & Comparative Endocrinology, which is now available online.

Now published in GCE!

Results published in GCE.

Stress is typically defined by duration—as acute or chronic— in the scientific literature as well as in veterinary and medical practices. I wanted to investigate not only stressor duration, but also other characteristics of the stressor, like frequency and intensity. There is some evidence that frequency and intensity affect the outcomes of stress, but few studies have attempted to look at how they might interact with each other or duration.

To test these ideas, I exposed fence lizards to different stress regimes. I did not want to use a physical stressor, so we instead manipulated a stress relevant hormone. When the stress response is activated, the glucocorticoid hormone cortisol (in humans) or corticosterone (in lizards) is secreted by the adrenal glands. We often measure CORT as a proxy for stress, and we can give a lizard CORT to replicate the increase in CORT that occurs in response to a stressor. After dissolving CORT in oil, one simply drops the solution onto the back of a lizard and it is quickly absorbed. One can also put the CORT-oil solution into a hormone patch for a slower release. These work a lot like a nicotine patch in humans, just with CORT and on a lizard.

A fence lizard with a slow release CORT patch.

A fence lizard with a slow release CORT patch. Stylish!

We used different regimes of CORT application to help determine how duration, frequency, and intensity affect immune outcomes in lizards. After the 9 days, we measured the innate immune system in two ways [similiar to  this post], both of which roughly measure the ability of lizard blood to deal with foreign particles. One of these assess hemagglutination, which is the ability of plasma to hold sheep red blood cells in suspension. Higher scores indicate greater ability, or better immune function.

The completed hemagglutination assay.

A completed hemagglutination assay.

Some of our results were particularly interesting:

Two of our treatments would be considered “acute.”  Both were short in duration and differed only in the intensity of the dosage. Exposure to short duration low-doses of CORT  enhanced immune function (hemagglutination), while exposure to short duration high-doses suppressed immune function. This indicates that intensity is an an important factor when considering immune outcomes of stress.  This matches up with what we know about PTSD—short but intense stressors can have lasting effects in that context as well.

Additionally, while both of these treatments mimic “acute” stress, they produced opposite results. This demonstrates that the terms “acute” and “chronic” may not be enough to sufficiently characterize stress. These terms are also inconsistently used in the scientific literature, which only adds to the confusion.

Three of our treatments received the same average amount and total amount of CORT over each three day period and over the duration of the experiment but differed in how they were distributed–they varied in duration, intensity, and frequency. All three of these treatments, however, produced different outcomes—one enhanced immune function (frequent low doses), one suppressed immune function (infrequent high doses), and one was somewhere in the middle (slow release of the high dose). This suggests that average or total amount of stress (CORT) may not be comprehensive enough to characterize how the stress is experienced or accurately reflect its outcomes.

Although frequency and duration had lesser roles in this experiment, intensity was a major factor in altering the immune consequences of stress. We recommend that researchers consider and report aspects of stress other than duration, such as intensity and frequency, to aid our understanding of the consequences of stress. We should also move away from the terms “acute” and “chronic,” as they are inconsistency used and incompletely describe stress.

Because the environment is changing due to climate and human activities, wild animals will be exposed to new stressors or familiar ones more often. Determining what about stress leads to negative consequences is important to understand how species will respond to environmental change.

How will wild organisms respond to the stress of environmental change?

How will wild organisms respond to the stress of environmental change?

These results are published in General and Comparative Endocrinology. This research is also featured on the Penn State CIDD website, here.


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New Kid on the Block

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).

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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.

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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.

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Me with a juvenile Common Water Snake (Nerodia sipedon) and Lilly with a Ring-necked Snake (Diadophis punctatus).


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From Brazil to Happy Valley

Hi everyone, my name is Braulio, and I’m one of the three new members of the Langkilde lab in 2015. I come from Brazil, where I got my bachelor’s degree in Biological Sciences from Universidade Vila Velha. My first research experiences as an undergrad were related to the effects of toxic compounds, natural or synthetic, on the activity of enzymes related to oxidative stress in plants and vertebrates.

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Me as an undergrad in Brazil

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After graduating, I joined the M.S. in Biology program at Adelphi University in Long Island, NY. Since then, my research interests have shifted towards the study of evolution, particularly sexual selection. Some of the questions I would like to answer in the future are why do some animals exhibit such unusual mating behaviors and under what circumstances can certain sexual traits become advantageous.

During my years at Adelphi I worked with a fascinating species of orb-weaving spider that has some unusual mating behaviors, including, but not limited to, sexual cannibalism and spontaneous male death.

Now that I am part of the Langkilde lab, I want to follow up on the research being done here and further investigate the adaptive significance of male ornaments on female fence lizards (a.k.a. “bearded ladies”). Since previous lab members have demonstrated that they are unattractive to males (as you would expect), we still don’t understand how they are so frequent in certain populations. We suspect that male ornaments might come as a side-effect of high testosterone, which could be advantageous to females in certain situations. For instance, they could be faster runners or exhibit more aggressive behaviors (stay tuned…).

In my free time, I like doing sports (especially swimming), playing Nintendo video games and playing the electric bass.

My first impressions of the lab, the people and the town of State College are that people are indeed happy here in Happy Valley. I like the friendly atmosphere and the variety of outdoors activities that can be done around here. I’ve been slowly getting into the some of American sports, mostly baseball and hockey. I still don’t get what’s the big deal with American football, but maybe being at Penn State will change that in the future.