Crayfishes compete for optimal water temperatures

The survival of many animals depends on their ability to compete for resources—food, water, shelter, or territory. But could optimal temperatures be an equally valuable resource for cold-blooded species—and a reason for territorial disputes? Canadian scientists led by Glenn J. Tattersall have observed this type of competition in the Louisiana Crayfish, Procambarus clarkii. When it comes to securing a territory with the right temperature, this crayfish shows behaviors similar to those seen in traditional intraspecific rivalries.

The behavior of the Louisiana Crayfish was recorded with video cameras and analyzed later. The experimental containers (so-called shuttle boxes) were divided in two. Using two computer-controlled coffee makers, each half was set to and maintained at a different temperature. First, the scientists identified the temperature at which the animals felt particularly comfortable and did not migrate into the other half of the box. The preferred temperature was 75°F (23.9°C).

In the next experiment, two specimens of the crayfish were placed in the test tank at the same time. One half was at the preferred water temperature, while the other side was either colder (71.2°F/21.8°C) or warmer (78.6°F/25.9°C). If the animals were familiar with each other and had already established a hierarchy, there was very little aggressive behavior. The dominant crayfish then occupied the part of the tank with the optimal temperature, while the weaker individual retreated to the other half. Occasionally, both crayfishes shared the preferred chamber.

However, if the two animals were unfamiliar with each other, they competed for the side with the preferred temperature. A hierarchy was usually established after half an hour, but the lower-ranking animal tried again and again to take over the side with the optimal water temperature.

The higher temperature of 78.6°F/25.9°C appears to stimulate those territorial disputes more than the cooler temperature (71.2°F/21.8°C). The biologists believe it is possible that environmental factors, such as the flow rate or the oxygen content of the water, could be the underlying resources the crayfish competed for!

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