The Whole World in a Drop of Water
—Taro Ietaka, Director of Conservation and Land Stewardship
A rotifer. Photo by rkitko on commons.wikimedia.org
Have you ever woken in the middle of the night with the terrible thought that the solar system might be contained in an enormous snow globe owned by a giant child? If not, you are lucky. But for some creatures living on this planet, this is a good analogy for their existence. Take bdelloid rotifers, for example.
These animalcules (very small animals) can be found in a wide variety of freshwater habitats, such as lakes and ponds. However, some of them have a much smaller view and spend their entire lives in the water held within a pitcher plant's leaves. Even that is roomy though, when compared with those that live sandwiched in a drop of water between the leaves of our locally common Frullania liverworts.
Frullania grows on the bark of trees and is almost universally overlooked. It has a dark, veiny growing habit and is often mistaken for cracks in bark. However, these liverworts are living plants closely related to mosses. Their leaves are arranged in overlapping scales, similar to roof shingles. They are able to withstand prolonged droughts, but when it rains they cling to water by cupping it between their millimeter-long leaves. This is the world of some bdelloid rotifers.
They feed by moving hair-like structures in a propellor-like fashion, thus creating a current that carries bacteria, algae, and other particles into their throats. They can also move in an inchworm-like manner, but as soon as the water in their world evaporates, they hunker down in a cyst-like ball until they are rehydrated. Perhaps the strangest path in the evolutionary history of bdelloid rotifers though, is that there are no males. Maybe it was just too hard to meet an attractive mate in a world so small, so the females just gave up and began reproducing parthenogenically (embryos develop from unfertilized eggs). Males then became superfluous and later non-existent. A nightmare come true!
Frullania liverwort. Photo by Bernd Haynold on commons.wikimedia.org
