The Lizard Log

The Langkilde Lab in Action

Does This Predator Make Me Look Fat?: Morphological Responses of Tadpoles to the Presence of a Predator

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Andrew Watts is a junior who is majoring in Biology with a Vertebrate Physiology Option and also minoring in Kinesiology. Outside of his studies, he is involved with THON, Camp Kesem, a summer camp for children affected by cancer, and works for Penn State EMS as an EMT. After graduation, Andrew is looking to attend medical school and pursue a career as a surgeon. Andrew’s post about his ongoing research in the Langkilde Lab is below.

I have been working in the Langkilde Lab with Brad Carlson, a graduate student, since Fall 2012 investigating the effects of predator cues on wood frog tadpoles. I am investigating morphological effects, which pertain to how the tadpoles change their size and shape in response to predators. We are attempting to look into whether or not the presence of a predator cue has a significant effect on a tadpole’s morphology, and how these changes make it adapted to living in an environment with or without predators. Also, another factor that we looked into was whether or not the previous adaptations of the first generation tadpoles collected had an effect on how the second-generation tadpoles changed in the presence of a predator cue. These same tadpoles were also part of other work looking into tadpole personality and traits, but I was only involved with the morphology aspect of the project.

The experiment actually started in the spring of 2012 when the original tadpoles were collected from many different ponds. They were all set up into large bins where some were exposed to a predator cue, and others were controls (no predator cue). The tadpoles exposed to a predator cue had a dragonfly larvae (a natural predator of tadpoles) in a small cage placed in the middle of the tube, while the control groups had nothing placed in their tubes. The dragonfly larvae released chemical cues into the tubs which tadpoles can detect as an indicator that a predator is present. If the tadpoles detected a predator, their morphology might change in response. During the time in which the tadpoles were alive they were videotaped for the purposes of the personality and traits experiment. When the trials were finished, the tadpoles were humanely euthanized, preserved in ethanol, and placed into the jars according to which experimental group they were in. Each group had approximately 60 tadpoles and 10 of these tadpoles were randomly picked to be weighed and have pictures taken in two different positions. This same routine was repeated for all of the groups (control and experimental). There were 38 total groups, so, in all, 360 tadpoles were weighed and photographed for a total of 720 pictures. This was an extremely long and time-consuming process!

Figure 1: These are examples of the two types of pictures that were taken. Each is of the same tadpole just taken at different angles so that the multiple morphological measurements could be taken.

Figure 1: These are examples of the two types of pictures that were taken. Each is of the same tadpole just taken at different angles so that the multiple morphological measurements could be taken.

Once all of the pictures were finally taken, I was able to analyze them using computer software called ImageJ. For each tadpole several different measurements were taken in order to get a complete representation of its overall morphology.

AwattsFig 3Comb copy

Figures 3 and 4: These are the reference guides that I used from previous tadpole morphology research done to measure the tadpoles.(Figure 3, Left: Rick A. Relyea (2001), Figure 4, Right: Ronald Altig (2007))

With all of the data collected I then analyzed it with Brad’s help. First, we found that tadpoles that were exposed to the predator cue were actually shorter and wider than the tadpoles in the control groups, which were longer and slimmer. The shorter, wider body types may allow these tadpoles to grow faster or survive better in the presence of predators. These findings were expected since previous research by Dr. Rick A. Relyea found that when tadpoles are exposed to predator cues they adapt by changing their morphology to a shorter and wider shape. However, we also tested if there was any significant link between what kind of pond the tadpole came from and the effect of the predator cue. As previously discussed the tadpoles were taken from many different locations, and some ponds were known to have predators present. This could have possibly primed or prepared the tadpoles to be able to better adapt to the predator cue. However, the results from our data did not show a significant relationship (p>0.05) between what kind of pond the tadpoles originally came from and how their morphology changed when placed in the presence of a predator cue. Even though our data supported the null hypothesis for this experiment, further research is still being conducted. There are many other groups of tadpoles from various experiments, and each has the possibility of revealing something else about tadpole morphology and evolution. This research can allow us to better understand how exposure of previous generations and their adaptations and personality traits can affect how future generations will adapt to different stimuli and changing environments.

My work and contributions in the Langkilde lab have given me a whole new perspective and appreciation for scientific research. I never fully understood the amount of time and effort that goes into the research. I also never fully understood how much evidence you need to have in order to produce significant findings and support a claim. I have also learned a great deal about ecology and especially predator prey interactions, which has even helped me in biology courses involving these concepts.

References:

Relyea, R.A. 2001. Morphological and behavioral plasticity of larval anurans in response to different predators. Ecology 82:523-540.

Altig, R. 2007. A primer for the morphology of anuran tadpoles. Herp Con Bio 2:71-74.

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