The Lizard Log

The Langkilde Lab in Action

Mark Measures Eggshells to See Who Has More

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As the summer field season winds down and school begins to pick back up, we’re going to start featuring guest posts by our undergraduate researchers to give you an idea of the breadth of the projects going on in the lab. First up is Mark Goldy-Brown, a rising senior at PSU who will be starting his second year in the lab this fall:

This past fall I started as an undergraduate researcher in the Langkilde Lab, and so far I have enjoyed every minute of my time here.  The lab is well known for studying the interactions between the Eastern Fence Lizard (Sceloporus undulatus) and the Red Imported Fire ant (Solenopsis invicta), an invasive ant species that had been causing many problems in the United States since it was accidentally brought here from South America over 80 years ago.  These fire ants cause a great deal of agricultural damage each year in addition to affecting native plants and animals, which are not adapted to handle this invasive species.  Some of the lab’s work focuses on how the fire ants affect the fence lizards in the southern U.S. and has shown that fence lizards seem to be adapting to deal with these nasty little ants.


Map showing where the females who laid the eggs used in my study were collected from. Invaded sites have fire ants, while uninvaded sites have no fire ants.

Most research so far has been to see how the fire ants affect the hatchling, juvenile, and adult lizards, but my research over the last year examined how the fire ants could be affecting the fence lizard eggs.  Fire ants are extremely aggressive predators, capable of attacking and eating nearly anything that they come across when they are searching for food, including reptile eggs.  They have been shown to eat the eggs of sea turtles, painted turtles, chicken turtles and even yellow rat snakes.  Last summer and this past summer, our lab showed that the ants will also eat fence lizard eggs.  Wow!  So I wanted to see whether there were any differences between eggs from populations of fence lizards that had been living with fire ants for many years and eggs from populations of fence lizards that had never been exposed to fire ants.  You would think that if fire ants can eat through the eggs, then perhaps eggs that are laid where fire ants are also found should have some added protection so that they have a greater chance of surviving.  My two hypotheses for this experiment were that eggs from sites invaded by fire ants would 1) have thicker shells and 2) more Calcium Carbonate (a crystal compound that could make it harder for fire ants to penetrate the eggs) than those from sites where no fire ants were present.

Testing these hypotheses involved working with a ton of fence lizard eggs (collected after the baby lizards hatched, of course).  To test my first hypothesis, I cut each eggshell in half, cleaned out the inside and then used a biopsy punch to remove equally sized bits along the length of the eggshell that I called eggdiscs.  These eggdiscs were placed in between two glass microscope slides and left to dry out in a container filled with silica beads (the silica removes water and dries them out).  Once they had all dried, I measured each of the eggdiscs (there were quite a few) using a thickness gauge that could measure very thin things with high accuracy.  After analyzing the data collected, I found that eggshells from uninvaded sites (no fire ants) were actually thicker than those from invaded sites (fire ants), the complete opposite of what I was expecting.  I wasn’t really sure why this would be the case, but I thought that perhaps mother lizards who aren’t stressed by fire ants can put more energy into their eggs and therefore make thicker ones.  Interestingly, I also found that thickness also varies within the eggshell, meaning that the tips of the egg are not the same thickness as the middle of the egg.

Diagram showing the eggdiscs on a slide, and how I sampled them along the whole length of an eggshell.

Diagram showing the eggdiscs on a slide, and how I sampled them along the whole length of an eggshell.

So my second hypothesis was that fence lizard eggs from invaded sites would have more calcium carbonate than eggs from uninvaded sites.  To test this theory, I used whole eggshells that came from the same mothers as the eggs used for the thickness experiment.  Each eggshell was cut in half, placed into a test tube and then stuck in a dehydrator (the same kind of one you would use to make dried fruit) for 2 days.  After they dried out, I weighed each of them and then added hydrochloric acid (the acid dissolves all of the calcium carbonate) and then let the eggs “soak” for 24 hours.  After they had sat in the acid for a day, I poured out the remaining liquid, dehydrated the eggshells again and then weighed them once more.  The difference in weight from before and after the eggshells were dissolved in acid is equal to how much Calcium Carbonate was present in the eggshell.  When I analyzed my data for this part of my project, I didn’t find any significant results but it did show a trend that there was more calcium carbonate in eggs from uninvaded sites than invaded sites, which again was contrary to my hypothesis.

I was very excited to complete my first full research project this past spring and to be able to present my research at the annual undergraduate research symposium.  Performing all of the data collection took me several months and it required a lot of repetitive work, but it definitely paid off.  After completing this project, I began to create a project to work on over the summer and this project will be the subject of a future post.  Hope you enjoyed hearing about my research project and pose any questions in the comments section!


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