Cell density-dependent swimming patterns of Alexandrium fundyense early stationary phase cells

摘要

Different life-history stages of Alexandrium fundyense have different swimming behaviors and show different responses to water movement. Early stationary phase cells assemble in bioconvection patterns along the water surface and as stripes in the water, while cells in exponential growth do not. We studied the swimming behavior of early stationary phase A. fundyense cells, both on the individual level and on the population level. Cells assembled in spots in shallow Petri dishes, and were studied using an inverted microscope. We analyzed 53 videos of cells at different distances from the center of accumulated spots of cells with the program CellTrak for swimming behavior of individual cells. The closer the cells were to the center of spots, the faster they swam (>600 mu m s(-1) in the center of spots compared to ca. 300 mu m s(-1) outside) and the more often they changed direction (>1400 degrees s(-1) in the center compared to <400 degrees s(-1) outside). On a population level, the behavior of spots of assembled cells was studied using time-lapse photo graphy. The spots entrained more and more cells as they grew and fused with each other; the closer the spots came to each other, the faster they moved until they fused. We suggest that chemical attraction between gametes causes the observed behavior.