| dc.description.abstract | Paramecium tetraurelia cells with cortical inversions are characterized by a 180° rotation of all the components of the ciliary rows (basal bodies and their ancillary structures) in a portion of the cortex. The power stroke of inverted cilia is “wrong-way” (towards the anterior) and produces a distinctive twisty or rotary swimming pattern. Although cortical inversions are heritable, some degree of artificial selection has been necessary to maintain the twisty swimming phenotype. The purpose of this project was to determine whether changes in the composition of the cortex are directly responsible for the “better” swimmers, as opposed to the cells adapting their swimming behavior by some other means. Another goal was to develop a quantitative relationship between swimming pattern (velocity, helical width and pitch) and number of inverted ciliary rows. We have found that cell populations can in fact spontaneously lose (or gain) inverted rows, and that, intuitively, inverts with fewer inverted rows are faster, swim straighter, and travel greater distances per helical turn. This suggests variants with fewer rows inverted have a functional and energetic advantage in competing for food resources in mass culture, resulting in an observed decline of mean inversion size over time. Overall, it is apparent that the cortex can undergo dynamic changes with measurable effects on swimming phenotype. These changes, divorced from any sort of genomic changes, nonetheless have profound effects on both cortical and behavioral phenotype, and can be stabilized or destroyed depending on the prevailing selective forces. This suggests structural inheritance may be highly significant to cortical stability and evolution in Paramecium. | en |
