Volvocacean family secrets to ponder upon a midnight dreary
A.W. Coleman
BioMed, Brown University, Providence, RI 02912
Some problems seem to get swept under the rug. Example: Flagella: A. Exactly how do colonies (and unicells) swim. Both unicells and colonies swim with a counterclockwise spiral. So also do all other flagellated unicells. Is it easier to screw through water molecules counterclockwise? B. One flagellar basal body is older than the other. The younger basal body is the one associated with the reassembled stigma in Chlorophytes, but the older is associated with the stigma in Chrysophytes. Why? C. The orientation of the basal bodies is often assumed to be stable. Yet , while flagella of colony vegetative cells flip in parallel, the same cells released as gametes display a breaststroke. Example: Environment: what are the environmental factors, nutritional and biotic, that act on these forms? Zygotes are clearly a development for survival. Colony size and speed are not so obvious. The most common forms in nature are Gonium pectorale and the Pandorina's - why? The former is a genetically uniform species; the latter is a tree of considerable genetic diversity, yet a grouping separate from any other colonials. Has Pandorina found the optimal morphology? And Volvox as a genus encompasses more genetic diversity than any other genus in the family, at least 16-17 species, yet colonies are rarely encountered in nature or germinated from mud samples. The majority of Volvox species are found only in snow-free regions. Why? The family keeps its secrets well.
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