Laboratory Notes for BIO 1003
© 20 April 2004, John H. Wahlert, Mary Jean Holland & Joan Japha
DRAFTJ. Japha (Tuesday, 12/16/08) & J. Wahlert
Anatomy of Daphnia
Daphnia are small crustaceans that inhabit lakes, ponds and streams. They eat algae, and in turn, serve as an energy source for larger predators such as fish or other zooplankton (i.e., small animals and protists of aquatic environments, like Hydra!). They capture algae (e.g., Volvox and Chlamydomonas) with their legs, which also serve as gills, helping them breathe oxygen from the water. Daphnia swim in a jerky fashion by thrusting downward with of a pair of powerful, double branched antennae, which is the reason for their common name water flea (Buchsbaum et al., 1987).
Daphnia have a single compound eye and an ocellus (a simple eye). They have two pairs of antennae (4 total), one pair for locomotion and one for sensing their environment. Their thoracic appendages produce a current of water to carry food particles to the mouth and oxygen to the gills. Because Daphnia exoskeletons are transparent, internal organs such as the beating heart are visible without dissection. Also, note that if one has eaten green algae, its gut may look green. (See Micscape Magazine photos.) A post-abdominal pair of claws is used to remove unwanted material that may have accumulated in the carapace. Males are smaller than females, but have hooks on their first pair of thoracic appendages to grasp females. The males have larger first antennae than females. (Clare, J. and Micscape Magazine)
Examine Daphnia in water. Place a single Daphnia in a drop of water on a depression slide and observe at low magnification. Sketch what you see and label the structures highlighted in boldface, above.
Ecology: Daphnia are sensitive to poor water conditions and therefore serve as bio-indicators (i.e., organisms which when present or absent reflect on water quality; See Clare, J.) By studying the effect of common pollutants such as alcohol, caffeine, and nicotine on Daphnia's heart rate, we can learn more about how chemicals affect aquatic organisms, and thereby the ecosystems of which they are a critical part. We can also compare the effect of chemicals on Daphnia to their effects on human physiology.
We will observe the effects of certain chemical compounds (see TABLE 1, below) on the heart rate of Daphnia.
Daphnia reproduce asexually and sexually. When food is abundant, Daphnia reproduces parthenogenetically. Parthenogenesis is a form of asexual reproduction where unfertilized eggs develop into zygotes. Under ideal environmental conditions, eggs produced this way all develop into females. If conditions are less favorable, some unfertilized eggs develop into males, and the subsequent generation will reproduce sexually. Fertilized eggs produced by sexual reproduction develop within the carapace. Like other crustaceans, a carapace covers the body, but in the female Daphnia, it also serves as a brood chamber for developing embryos. The egg-housing part of the carapace is called the ephippium because it is shaped like a saddle. When sexually-produced eggs leave the female, they enter a suspended state where they are able to resist drying and freezing, and they can survive the winter and hatch in the spring. (See Clare, J.)
Return to index.jj filename: daphnia lab JJTH draftl4Dec08
Last updated 7 Augustl 2010 (JHW)