The Lizard Log

The Langkilde Lab in Action


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Maternal glucocorticoid effects across life stages in fence lizards – new paper!

“Anthropogenic disturbance is a growing threat, and the physiological consequences of exposure to such stressors is gaining increasing attention. A recent paper published in the Journal of Animal Ecology explores the consequences of stress-relevant hormones for mothers and their offspring…”

Read more in David’s new paper, and featured blogpost on the Journal of Animal Ecology blog!

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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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Undergraduate research in the spotlight!

The Langkilde lab was well-represented at this year’s Undergraduate Research Symposium by three of our lab researchers! It’s been an excellent year for undergraduate research. Congratulations to Richard Novak, Kristen Sprayberry, and Andrea Racic on their poster presentations! Not pictured is Jennifer Heppner, who also completed a brilliant thesis in the Langkilde lab this year. It’s been a pleasure having you all in the lab, and we will be sorry to see you go – but look forward to hearing about your future endeavours!

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A New Blood Sampling Method for Smaller Anurans that Preserves Critical Features of Specimens

Another new paper from Dustin In Herpetological Review! Summary below.

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Obtaining adequate blood samples is vital for most studies involving immunology or physiology. Anurans (frogs and toads) present a particular challenge for obtaining adequate samples, largely because of their relatively small size compared to other vertebrates.

Here, we propose a new method for obtaining large amounts of blood from the ventral abdominal vein of euthanized frogs, which we call the lethal abdominal vein of anurans (LAVA) technique.

We tested this method on the locally common Wood Frog (Lithobates sylvaticus –  pictured above). Using the LAVA technique, we were able to collect blood from 100% of frogs. Each frog yielded an average of 0.09 mL (range: 0.03 to 0.17 mL) of blood, which contained an average of 40 µL (range: 15 to 100 µL) of plasma.

We also found that neither size, ambient temperature, nor site affected our blood yields. We show that the LAVA technique is an easy-to-use method that yields high amounts of blood from anurans, and could be potentially viable in other small vertebrates.


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Offspring influenced by their evolutionary history more than their own experience in fence lizards

Check out the first chapter of Dustin’s thesis on the “Trans-generational but not early life exposure to stressors influences offspring morphology and survival”, recently published in Oecologia!
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Environmental changes, such as the introduction of non-native species, can impose novel selective pressures. This can result in changes in fitness-relevant traits within an individual’s lifetime or across multiple generations. We investigated the effects of early life versus trans-generational exposure to a predatory invasive insect stressor, the red imported fire ant (Solenopsis invicta), on the morphology and survival of the eastern fence lizard (Sceloporus undulatus). We captured gravid lizards from high-stress populations with long histories of invasion by fire ants and from uninvaded sites. Resulting hatchlings were exposed weekly to one of the three treatments until they reached maturity (42 weeks): (1) sub-lethal attack by fire ants; (2) topical application of the stress-relevant hormone, corticosterone (CORT), to mimic the stress of fire ant attack; or (3) control handling. Exposure to post-natal early life stress (fire ants or CORT) did not interact with a population’s evolutionary history of stress to affect morphology or survival and early life stress did not affect these fitness-relevant traits. However, morphology and survival were associated with the lizards’ evolutionary history of exposure to fire ants. Offspring of lizards from fire ant invaded sites had longer and faster growing hind-limbs, gained body length and lost condition more slowly in the first 16 weeks, and had lower in-lab survival to 42 weeks, compared to lizards from uninvaded sites. These results suggest that a population’s history of stress/invasion caused by fire ants during ca. 38 generations may be more important in driving survival-relevant traits than are the early life experiences of an organism.

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You can read more about Dustin’s research here and here! 


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Testing the environmental matching hypothesis – return to Alabama!

Another summer field season has now come and gone! This summer I returned to Solon Dixon Forestry Education Center in Alabama (one of my favourite spots on earth!) to continue my research on how stress during gestation influences the offspring of eastern fence lizards (Sceloporus undulatus).

Last year, we investigated how physiological stress during gestation (at the level of a non-lethal predator encounter – for example, when a lizard encounters a couple of toxic fire ants, but isn’t killed by the ants) affects survival of mothers, and how many of their eggs successfully hatch. You can read more about this experiment, and the fieldwork that went into it, here (and stay posted for the published results soon!).

This year I wanted to build on these results and ideas to test how maternal stress influences the offspring that do hatch and make it out into the world. Do they themselves then cope better with a stressful environment, having been “primed” for it by their mothers (the “environmental matching” hypothesis)? Or are offspring born to stressed mothers poorer in quality, and less likely to survive in the wild, regardless of how stressful their environment is? In order to test these ideas, we first made the long trip south to collect gravid females from south Alabama early in the summer, and to build experimental enclosures in which to eventually release their offspring. I then repeated the maternal stress treatment from last year and once again became a lizard mama as I followed the females from laying their eggs, to incubating the eggs, and eventually seeing these bite-sized babies hatch out!

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Freshly hatched fence lizards – <1g!

Once they hatched, the offspring went into the enclosures that we’d built. These enclosures were designed to test whether maternal stress programs offspring to be able to better deal with a stressful environment. The enclosures either contained a key stressor (invasive fire ants), or were fire ant-free. Each day I conducted a mini-census, walking through enclosures to look for each lizard – as you can see in the video below, babies were marked so I could tell exactly who was present each day (and so, which lizards survived, and which didn’t). I also observed their behaviour, and how they used the habitat available to them (for example, did offspring from stressed/non-stressed mothers differ in whether they liked to be out in the open, like the lizards you see in the video – or did they hide more?).

After a great summer (if measuring 200+ baby lizards isn’t a metric of a great summer, I don’t know what is), I’m now back at Penn State with a box of data to work through. I’m excited to report back on what I found in the coming months – so stay tuned!

 

 

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Hanging out with an adult female Sceloporus at Solon Dixon

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Beautiful Solon Dixon


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It’s fieldwork season!

The lab is currently busy with a variety of field and lab-based projects. In April/May, Cam, David, Tom, and I were in Alabama collecting lizards. Here’s a glimpse of what the long trip to the South, and our work there, looks like! Check back later in the summer for more on the continuation of this project.