Evolution

Copepods (tiny crustaceans) change their stroke style in different water temperatures. Copepods have three pairs of appendages. In warm water, copepods use a wave-like stroke, where the first pair take a stroke and the second pair start their stroke before the first pair have finished, and so on to the third pair. In cold water, copepods use a "power stroke," where the second pair don't begin their stroke until the first pair finish their stroke, and so on to the third pair.

Why do they change their stroke? It turns out that temperature affects the muscles in the copepod's appendages. This is beneficial for the copepod, because it turns out that in colder temperatures the water is more viscous and the wave-like stroke makes the copepod more vulnerable to predation. The power-stroke is less efficient, but predators have a harder time catching the copepod with this stroke in cold water.

In viscous, warm water, the copepod still uses the wave-like stroke, and is more vulnerable to predators. This situation occurs in algal blooms.

Photo courtesy of:

http://www.microscopy-uk.org.uk/mag/indexmag.html?http%3A%2F%2Fwww.microscopy-uk.org.uk%2Fmag%2Fwimsmall%2Fcrust.html

Sources:

http://www.sciencedaily.com/releases/2013/04/130402124819.htm

http://www.pnas.org/content/110/12/4661