Behavior of cellular slime molds in the soil.

Cellular slime molds are soil organisms, yet since they were discovered in 1869 they have been studied on agar surfaces. Here the behavior of a number of species is examined and it is evident that they have different responses to directional light and they all thrive in the presence of soil. While phototaxis clearly plays a significant role in their ability to come to the soil surface for dispersal, even more important are gradients in the soil: both temperature gradients known from earlier studies, and as we show here gas gradients, presumably ammonia as a repellent and oxygen as an attractant. There are numerous differences in both morphology and behavior among slime mold species, some of which are likely to be the result of natural selection to particular habitats, while others could be explained more easily by neutral phenotypic variation.