Alessandra Jimenez, Whitworth University
As this internship has recently come to an end, I now begin to reflect on the wonderful yet challenging experience I had conducting observational research on Atlantic brown shrimp (Farfantepenaeus aztecus). In the last few weeks of this 10-week summer program, there was a fascinating yet unexpected turn of events. In particular, results of the experiment pointed to conclusions that I initially found myself unprepared for!
In summary, the focus of this experiment was to test effects of immune response on the ability to escape predators in shrimp. The escape mechanism, called tail-flipping (see video below) is actually powered anaerobically. However, recovery from this energetic behavior absolutely requires oxygen (is aerobic). As further explained in previous blog posts (click here and here), a recently discovered consequence of mounting an immune response against bacterial infection involves depression of aerobic metabolism. So, my mentor and I decided to focus on the recovery aspect (aerobic) of the escape response and predicted that this aerobic process would be impaired in shrimp injected with bacteria. At the same time, we predicted that the anaerobic part of this mechanism would be significantly impacted.
A slow-motion video of an Atlantic brown shrimp juvenile tail-flipping in an experimental tank (c) Alessandra Jimenez
The last few weeks of the internship mainly consisted of analysis, arriving at conclusions, and publicly reporting results. After testing tail-flipping ability (click here for an explanation of how this was tested) in a total of 42 shrimp juveniles, 30 of these were chosen for final analysis. Using a statistics software called Sigmaplot (version 12.5), I conducted tests that basically compared experimental groups based on the two variables I investigated: treatment type (bacteria or saline) and time given after injection (4 or 24 hours). Afterwards, results were deemed important based on significance values assigned by these Sigmaplot tests.
Significant results were very surprising! Overall, results suggested that metabolic depression (indirectly caused by the immune response) did not have an impact on recovery (aerobic). At the same time, the most unexpected finding of all suggested that bacterial exposure actually increased anaerobic tail-flipping activity in Atlantic brown shrimp juveniles! Thus, this result called for a complete change in focus from the aerobic part to the anaerobic part of this particular escape response.
So, how could I possibly explain the increase in anaerobic processes found through this experiment? After much pondering and going through scientific literature, I formulated a new hypothesis. An important enzyme in crustaceans called arginine kinase is involved in the storage and creation of anaerobic energy that can be used for tail-flipping. Recent studies involved injecting bacteria into live crustacean tissue and comparing arginine kinase expression levels with controls. Results indicated a significant increase in expression in bacteria-injected tissue, especially in abdominal muscle (important for tail-flipping!). Based on these investigations, I now think that there may be a link between immune response and levels of anaerobic metabolism. Further research is required to explore this.
The final stages of the internship included creating and presenting a Powerpoint presentation of our work, and submitting a manuscript of my summer investigation. Overall, this REU internship experience has been challenging yet exciting, and has confirmed my love for marine biological research. As I mentioned at the end of my presentation, “expect the unexpected in science”.
Picture of me right before giving my Powerpoint presentation (c) Alessandra Jimenez
Burnett, L. E., Holman, J. D., Jorgensen, D. D., Ikerd, J. L., & Burnett, K. G. (2006). Immune defense reduces respiratory fitness in Callinectes sapidus, the Atlantic blue crab. Biological Bulletin, 211(1), 50-57.
Gruschczyk, B., Kamp, G., 1990. The shift from glycogenolysis to glycogen resynthesis after escape swimming: studies on the abdominal muscle of the shrimp, Crangon crangon. J Comp Physiol B, 753-760.
Scholnick, D. A., Burnett, K. G., & Burnett, L. E. (2006). Impact of exposure to bacteria on metabolism in the penaeid shrimp Litopenaeus vannamei. Biological Bulletin, 211(1), 44-49.
Yao, C., Ji, P., Kong, P., Wang, Z., Xiang, J., 2009. Arginine kinase from Litopenaeus vannemai: Cloning, expression, and catalytic properties. Fish Shellfish Immunol 26, 553-558.
Many thanks to College of Charleston for hosting my project, Dr. Karen Burnett and Hollings Marine Laboratory for guidance and work space, and NSF for funding the REU program.