This week has been one of the most interesting weeks of my project so far because I got to dig through my data to see what was hiding therein. I finished up my dataset at the beginning of the week, save for one experiment to account for the effect of gravity. This left me a lot of time to analyze the data, make plots, and draw conclusions. I’m happy to report that my data ended up looking great! The relationships that I was interested in all ended up being linear, which was consistent with my hypotheses. Based on the above graphs, beat frequency has a large effect on the swimming speed of the organism. As the beat frequency increases, swimming speed significantly increases regardless of whether body size was accounted for. However, the size of the organism does influence their swimming speed, as beat frequency is more strongly correlated to normalized swimming speed, meaning swimming speed divided by body length, than absolute swimming speed, which did not account for body size. This is consistent with previous results from Matsumoto 1991, but also shows that beat frequency is one of the primary drivers of swimming speed in these organisms. In addition to swimming speed, I was also interested in how different morphological features of these organisms change across their size range. I hoped that investigating these relationships would provide insight into the swimming speed trends shown above. As can been seen in the above graphs, as the body length of these organisms increases, a variety of metrics relating to ctene morphology significantly increase. These results may give some insight into why bigger organisms swim faster. Bigger organisms have longer ctenes, longer ctene rows, more space between the ctenes, more ctenes per row, and inflection points closer to the tips of the ctenes. These morphological features likely allow larger organisms to swim faster by allowing for increased power output of their metachronal waves compared to smaller organisms. It has been shown previously that increasing beat frequency leads to increases in power output of metachronal waves in Pleurobrachia (Barlow and Sleigh 1993, Dauptain 2008). My results, in combination with previous research, suggest that the above morphological features may play a role in the observed increase in power output, and subsequently the observed increase in swimming speed, as beat frequency increases. It would be interesting to quantify the relationship between swimming speed and these various morphological features.
I ran statistical analyses on all the above relationships and the slope of each regression line is significantly different from zero, which means that the increases in the independent variables, beat frequency and body length, do have a significant impact on the relevant dependent variables. These results are exciting for many reasons. For one, my experiment worked and I got good data! The results also support my hypotheses and there are a lot of implications that can be drawn from that support. Knowing how ctenophores like Pleurobrachia swim gives us more insight into how these organisms function as members of the planktonic ecosystem. I’m currently working through some papers that talk about the role of Pleurobrachia as a predator in planktonic ecosystems with respect to their influence on trophic structure. I think that my results will help give more insight into how Pleurobrachia have managed to have such a large impact on their ecosystem. I also think this provides evidence for a general trend in the plankton in which organisms modulate their swimming speed primarily through the beat frequency of their swimming structures. This is based on results from Murphy et al. 2011, which showed that increased beat frequency of krill pleopods led to increased swimming speed. It would be interesting to compare my results to the swimming performance of other ctenophores and other planktonic organisms that use metachronal swimming to build support for this general trend. My challenge now is to assemble all the plots and other figures I need to effectively convey my results. I will soon be making a poster in an attempt to summarize my project, which I know will be quite difficult. However, I am quite content at the moment as my project seems to have gone swimmingly. References: Barlow, D., & Sleigh, M. A. (1993). Water Propulsion Speeds and Power Output by Comb Plates of the Ctenophore Pleurobrachia Pileus Under Different Conditions. Journal of Experimental Biology, 183(1), 149–164. Dauptain, A., Favier, J., & Bottaro, A. (2008). Hydrodynamics of ciliary propulsion. Journal of Fluids and Structures, 24(8), 1156–1165. https://doi.org/10.1016/j.jfluidstructs.2008.06.007 Matsumoto, G. I. (1991). Swimming movements of ctenophores, and the mechanics of propulsion by ctene rows. In Coelenterate Biology: Recent Research on Cnidaria and Ctenophora (pp. 319–325). Springer, Dordrecht. https://doi.org/10.1007/978-94-011-3240-4_46 Murphy, D. W., Webster, D. R., Kawaguchi, S., King, R., & Yen, J. (2011). Metachronal swimming in Antarctic krill: gait kinematics and system design. Marine Biology; Heidelberg,158(11),2541–2554. http://dx.doi.org.ezproxy.library.wwu.edu/10.1007/s00227-011-1755-y
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AuthorMy name is Wyatt Heimbichner Goebel and I am a marine biology major at Western Washington University. I love biology, specifically marine mammal ecology and biomechanics. I’m always up for conversations about music, poetry, and weird biology facts. Archives
August 2018
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