Cricket Respiration Rates Under Differing Environmental Stresses
Aaron Richman, Jess Monical, Clark Miller, Will Seith
CU Boulder, Fall 2003
We wanted to evaluate the effects of different environments on crickets. More specifically we wanted to determine which environmental conditions produce the greatest change in a crickets respiration rate. As the crickets react to their environments their tissues will require either more or less oxygen to conduct cellular respiration. The more stress an environment puts on the cricket, the more oxygen they will need to deal with it. The increased respiration rate will also show up as an increase of CO2 production as the crickets. Though crickets do not posses lungs, their bodies do absorb oxygen and release CO2 as a function of their activity. We hypothesized that all of our different environments would cause an increase in the respiration rate. Furthermore since activity generally causes the greatest increase in respiration rates, we decided that a moving environment would produce the greatest increase, followed by temperature. After temperature would be light intensity. Since crickets are nocturnal darkness should make them become more active, intense light should slow them down.
To test our hypotheses we examined four different types of stresses; temperature, motion, visual and auditory. We placed approximately 1 gram of crickets in a sealed chamber and attached a probe measuring CO2 concentration. We then subjected the crickets to the different environmental variables. For the intense light we surrounded the chamber with lights, we used water bottles as heat sinks in front of the lights. We created a dark environment by wrapping the chamber in foil. Motion was created by shaking the jar. For auditory stimulation we tapped the side of the container in an irregular way to prevent them from acclimatizing to the noise. To vary temperature we used a steam bath and an ice bath. Each trial lasted 10 minutes. To avoid overstressing the crickets we also tried to use different individuals for each trial and let the crickets rest in between. We predicted that light intensities would produce the smallest increase, that temperature would cause a moderate increase and that shaking/tapping would elicit the greatest response.
Under normal temperature and light conditions the change in CO2 was 22.23 ppm/min/g. Under intense light, Darkness, tapping, shaking, heat and cold were, 34.07, 48.60, 60.29, 90.65, 277.8 and 10.87 respectively. Unfortunately since we did not conduct multiple trials for each stress we were unable to conduct a statistical analysis on all of our results. Under regression temperature data produced a line with an R squared value of .9127 and a Significance F of .191.
Though our data did not show a significant link between the environment and the respiration rates of crickets, trends in our results hinted that our predictions were correct. The rate was higher for every different environment except for cold. We now think that the data for temperature demonstrates the crickets sensitivity to heat as they are cold blooded. The increase under heat and a decrease while cold shows how their metabolic reaction kinetics can change. Shaking and tapping did produce large jumps in respiration, consistent with our predictions.
In retrospect this experiment was a bit over ambitious and unfocused. Had we decided to evaluate the effects of just one of our stressors we would have been more able to obtain significant results. One of the ways we could have improved on our experiment would be to conduct multiple trials for each stressor to establish a good statistical analysis of our results. Another problem was leakage during the tapping experiment; the cap may not have been completely sealed since our CO2 concentration showed huge dips and spikes, something we did not see in the other trials. Also we inadvertently killed the crickets in the heat trial, so we need to retest that variable under less extreme conditions. Results from the 2002 CABLE website showed that other experimenters showed trends in data similar to ours. According to Dimand et al. 2002 exercising crickets had a higher rate of respiration. Martin and Knapp. 2002, predicted light would have the same effect we did, however their data contradicted ours. They showed that respiration was significantly higher in a lighted environment than in a darkened one. In the future it would probably be more useful to evaluate the effects of each of these stressors independently; a more focused experiment would produce more telling results.