The Effects of Temperature on the Heart Rate of Daphnia Magna

Daphna Magna is a widespread zooplankton commonly found on fresh water. Their body temperature fluctuates with the environmental temperatures because it is an ectothermic animal. Therefore, there is an optimum temperature range, beyond which they are unable to perform most of their physiological processes properly. It is hypothesized that most physiological processes occur faster at higher temperatures than at lower temperatures, the heart rate of Daphna Magna will be faster as the temperature of the water in which it resides is increased up to a certain level (Betini, Roszell, Heyland, and Fryxell, 2016, p.20). The test conducted on Daphna Magna was geared towards understanding the effects of temperature changes in the water in which the animal resided and examining the effect of these shifts on the overall heart rate of the organism.

Methods

1. Take a Daphnia specimen and grease mount it into a cooled beaker

2. Add pond water to a petri dish that is taken from the same beaker as the Daphnia

3. The petri dish containing the Daphnia should be placed in a larger dish that contains a mixture of ice and water

4. Check if the heartbeats of the Daphnia with the lamp being approximately 10cm away from the dish

5. Turn the lamp off and wait for about 10 minutes for acclimatization and check the temperatures of the small petri dish. The temperature should be below 10 degrees Celsius (About 2- 3 degrees Celsius below 10 degrees Celsius)

6. Turn the lamp on and when temperatures approach the 10 Degrees Celsius mark, count the heart beats for the Daphnia and record it.

7. Repeat the measurements under the same temperatures while recording them to get an average

8. Convert the number of beats per 10 seconds to beats per minute and obtain an average of the two readings obtained above

9. For every increase in 2 Degrees Celsius, record the heart rate over 10 seconds of the Daphnia until the temperature is about 22 degrees Celsius

10. Repeat step 7 and 8 to get an average mark in each record made

Results

At the 2-3 degree Celsius intervals, Q10 was found to be about 1.32 but this was not the highest value for Q10, thereby not the most sensitive temperature interval. The decrease in heart rate, however, was noted in the lower temperatures as compared to the higher temperatures (See Figure 1 below). The heart rate at 2-3 degrees Celsius was found to be about 106.70 beats per every minute, which was lower than the heart rate 10-13 degree Celsius temperatures of about 140 beats per minute. The low heart rate at the 3 degree Celsius mark compared to the ambient room temperatures (about 22-24 degrees Celsius) is an indication of increased physiological activities as temperatures increase. Consistently increased sensitivity of the organism was observed between the increases in temperatures from 10 – 22 degrees Celsius (See Figure 1 below) with the beats per minute rising as temperatures increased.

Discussion

            It is evident that all organism operate at various temperatures and can achieve optimum physiological processes at a given range of temperatures. According to Kundu, and Singh, (2018, p.12), for Daphnia Magana, the temperature range from 10 – 30 degree Celsius provides the optimum physiological processes based on the increased heartbeats per minute. Therefore, temperature affects the overall performance of the organism. Since Daphnia is endothermic, the body temperature varies with that of the environment and thus the organism cannot thermoregulation (Adam, and Zofia, 2015, p.1). As a result, an increase in the temperature of the water resulted in an increase in the heart rate of the organism because less oxygen is present in warmer water, thus requiring faster pumping by the heart.

Figure 1: Heartbeat rate over the increase in temp

            Although the value of Q10 is predicted to be higher in lower temperatures and lower at higher temperatures, the findings of the study did not support this prediction. Q10 was higher in the high temperatures and lower in the lower temperatures. According to Barbosa, Pestana, and Soares, (2014, p5), this is possible because Daphnia is more sensitive to the environment at higher temperatures. However, Hoefnagel, de Vries, Jongejans, and Verberk, (2018, p.40) argue that the value of Q10 would also appear in such a manner due to errors in the experiment. Therefore, various factors may contribute to the Q10 value being different than the predicted value.

Conclusion

            The heart rate of Daphnia is directly affected by the temperatures of its surrounding. From the experiment conducted, as the temperature of the environment for the organism increases, the heart rate also increases due to higher physiological processes. Consequently, a decrease in the temperatures around Daphnia will result in reduced heart rates.

Bibliography

Adam, B. and Zofia, S., 2015. Subchronic Effects of Ectoine on Survival, Growth and Physiological Parameters of Daphnia Magna. Journal of Aquaculture Research & Development, 6(8), p.1. Retrieved from https://www.researchgate.net/profile/Zofia_Stepniewska/publication/282401741_Subchronic_Effects_of_Ectoine_on_Survival_Growth_and_Physiological_Parameters_of_Daphnia_Magna/links/564d822708aeafc2aaafe9ee.pdf

Barbosa, M., Pestana, J., and Soares, A.M., 2014. Predation life history responses to increased temperature variability. PloS one, 9(9), p.2-15. Obtained from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4176018/

Betini, G.S., Roszell, J., Heyland, A. and Fryxell, J.M., 2016. Calcium interacts with temperature to influence Daphnia movement rates. Royal Society open science, 3(12), p.16-24. Obtained from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5210679/

Hoefnagel, K.N., de Vries, E.H.J., Jongejans, E. and Verberk, W.C., 2018. The temperature‐size rule in Daphnia Magna across different genetic lines and ontogenetic stages: Multiple patterns and mechanisms. Ecology and evolution, 8(8), pp.38-49. Obtained from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5916275/

Kundu, A. and Singh, G., 2018. Dopamine synergizes with caffeine to increase the heart rate of Daphnia. F1000Research, 7. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6024234/