Adaptation

The Daphnia pulex has acquired many characteristics in order to adapt to its environment. Many of these characteristics are structural and have to do with the organism’s morphology, while others have to do more with the behavior of the organism.

The first important adaptation D. pulex and all other Daphnia have acquired is their carapace. This is a hard shell surrounding their soft body for protection. Without this, they would be extremely vulnerable to the environment surround them.

This picture demonstrates the presence of a carapace. This photo is actually one of D. magna; however, D. pulex has the same carapace structure.

 

Because the Daphnia pulex is denser than the water it lives in, it has developed a unique way in which it moves in order to avoid sinking to the bottom of its freshwater environment. The organism uses its muscles to beat the second set of antennae, which actually pushes them through the water. This “hopping” motion is actually where they obtained the common name of the water flea due to similar movement to that of the terrestrial flea. When Daphnia are in more of a sedentary mood or are in need of a good meal, they can then put those appendages at rest and roam around the muddy bottom in search for food particles.

The Daphnia pulex has also acquired many sensory adaptations to be able to respond to its aquatic environment. The nervous system consists of a primitive layout of nerves to the ganglion. This water flea also has developed a compound eye to help it sense its surroundings of the aquatic habitat. In addition, they also have a light-sensing organ                              similar to that of a tiny eye called an ocellus. Lastly, D. pulex can actually detect and respond to chemical cues from predators, mates, and even food!

This above photo clearly indicates one of D. pulex's
 sensory structures, the compound eye.

Another incredible adaptation among D. pulex includes their ability to actually change form in presence of a predator in order to be a less suitable food source. This is called cyclomorphosis. A decrease in size is often common when the adult fish populations are high. This adaptation makes it difficult for the larger organisms to spot the little creatures hopping along in the water. In addition, Daphnia will often increase in size when the young population of fish is more abundant, making it more difficult for the smaller fish to eat. Check out this cool news article about cyclomorphosis to learn more!

Lastly, one of the main adaptations to its environment Daphnia have developed is its ability to alternate between sexual and asexual reproduction, as mentioned earlier when discussing the life cycle. Remember, asexual reproduction includes the female reproduction process of parthenogenesis. This is when the female simply makes clones of itself without any fertilization of eggs. However, when conditions are unfavorable to Daphnia, the organism actually chooses to undergo sexual reproduction. In this case, male Daphnia and female Daphnia are both produced. When the male matures, he can then fertilize the female’s eggs which are encased in tough shells that can resist many severe weather conditions. This is an incredible adaptation the water flea has made to its tough environment!

 

Find out about what the organism eats. 

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