|MadSci Network: Zoology|
Daphnia is a curious little freshwater crustacean that is commonly used in classroom studies to observe things like heart rate. One of the most interesting things about them (in my opinion) is the fact that almost all of them are female! Most of the time they reproduce via parthenogenesis, a process where unfertilized eggs develop into genetically identical daughters. Thus no sperm, and therefore no males, are needed during the summer growing season. During these months the females are almost always gravid (carrying developing babies in their bodies). It is only at the end of the season when fall approaches and life will generally become more difficult, that males are produced and the Daphnia reproduce sexually.
For that reason, it is very difficult to find information on heart rate in male Daphnia. Most of the Daphnia in a population are females and gravid (i.e., "pregnant"). Generally speaking, the biological processes in Daphnia are temperature-dependent. This means that the heart rate speeds up at higher temperatures and slows at lower temperatures. If you are thinking about an experiment looking at heart rate in Daphnia, you might want to consider measuring heart rate at various temperatures to see this effect for yourself. You can then decide on which temperature would be the best for carrying out any other experiments you want to do.
Allison J. Gong
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