SOLVING PUZZLES

The tardigrade lives a paradox. How does it maintain life while passing through the freezing or boiling points where the water molecule needed for metabolism expands as it changes states? How does it prevent the cells from rupturing? Answers to these puzzles are beginning to emerge with research. For example, in the anhydrobiosis type of cryptobiosis a tun is formed as the tissue dries out and the water is replaced by the disaccharide sugar trehalose. Metabolism is stopped and the trehalose forms membranes that inhibit the expansion of the remaining fluids (Roser and Colaco 1993).

Many puzzles about tardigrades and life await to be solved. For example, only ten years ago Kristensen (1987) stated that the 130 plus species of the genus Echiniscus were completely parthenogenic, that is composed of only females. He proposed that over time males became smaller and less frequent as a percentage of the population. Thus the presence of large and abundant males is thought to be a statement of an evolutionarily older and more primitive condition. Pilato (1979) speculated that parthenogenesis was an adaption for successful passive distribution of cryptobiotic tardigrades because a single animal reaching an isolated location has better chance of surviving and procreating than if two individuals of different sexes are required.

About the same time, Dastych (1987) identified males in the genus Echiniscus by describing differences in the gonopores of specimens collected in the Himalayas and Antarctica. A few years later Claxton (1991) reported Echiniscus with large and numerous males in the mountains of Southern Australia. Then Miller and Heatwole (1994, 1996) found males on the Mawson Coast and in the Prince Charles Mountains of East Antarctica. Most recently, Claxton (1996) has described several new species of Echiniscus from Australia that exhibit sexually dimorphic characteristics in additional to the gonopore. Because of this recent evidence, we must rethink the basic assumptions of the role of parthenogenesis and cryptobiosis as adaptations for survival in harsh, isolated situations.

Like a puzzle or a mystery, the pieces of evidence unfold, one report at a time. You work with your data, you read what others find, and you look for patterns of sameness or contradiction. You challenge how each fact fits into the puzzle. This is the adventure of science. There are many biological puzzles waiting to be answered by the observant student. Most tardigrade work does not require expensive equipment, only the tools found in a biology classroom. It just takes a little interest and patience.