Powers of Two, a talk by Dr Kirsty Wan (University of Cambridge)
Abstract
Aqueous environments, with which we are familiar, such as puddles, rivers, ponds, and oceans, are teeming with microorganisms. Research into the myriad swimming or motility strategies adopted by these creatures has undergone a major revival in recent decades. Often propulsion is generated by the vigorous beating dynamics of organelles known as cilia and flagella — the eukaryotic version (with which this talk shall be concerned) comprises active elements along its length in the form of dynein motors, which modulate flagellar waveforms in response to mechanical and/or biochemical cues.
Like microscopic analogues of limbs, flagella often come in pairs… The twin anterior flagella of the tiny alga Chlamydomonas reinhardtii executes a bilateral breaststroke when actuated synchronously, but when this bilateral symmetry is broken, they are also capable of turning the cell. The latter phenomenon underlies tactic reorientation, which brings cells closer to sources of light or nutrients. The phylogenetic lineage to which Chlamydomonas belongs has at the other extreme the large spherical algaVolvox carteri: adult colonies possess dense coverings of biflagellate somatic cells whose flagellar beating exhibits remarkable spatiotemporal coherence, much like the cilia in our lungs or metachronal waves in a football stadium. From the few to the many, how do these cilia and flagella coordinate their beating in the absence of a brain or semblance of a nervous system? More fundamentally, we wish to understand the nature of pairwise interactions between flagella, through a combination of theory and experiment. We shall conclude by exploring the evolution of yet more sophisticated flagellar coordination mechanisms found occurring in Nature.
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