CONICET | Buscador de Institutos y Recursos Humanos

The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to bethe closest living relatives of the animals, their sister group. The changes in gene content that preceded theorigin of animals can be reconstructed by comparison with them. Choanoflagellates Salpingoeca rosetta,under suitable environmental cues can differentiate into two types of solitary cells. Each group is recognized byits own swimming strategy and its body size: fast and small or slow and large. Under nutrient limited conditions,S. rosetta experience a haploid-to-diploid transition, evidenced by the presence of gametes. It is challenging todetermine if there is a connection between the two types of cells and the male and female gametes. Here is wheremicrofluidics can play an important role in evolutionary biology, if it helps to isolate and concentrate the fastcells because under laboratory conditions always they are mixed populations. Motivated with this currentinterest, we have measured their sizes and characterized their motilities, developing a new soft for automatictracking analysis of big amount of data [Sánchez et al, 2016, ReyesThesis2017, ReyesPreprint2018]. We findthat fast cells swim remarkably different from slow cells, being their trajectories quasi-straight and interruptedby changes of direction while the latter are strongly tortuous. We propose a phenomenological model toreproduce the observed choanoflagellate dynamics. Further, cells are confined into a flat device divided by awall of asymmetric obstacles separated by micro-gaps. A systematic study of the directed transport is performedin order to optimize the device geometry. We solve the Langevin dynamical equations of motion using theexperimental parameters. Simulations show that fast choanoflagellates are remarkably easier to be directedefficiently for a wide range of wall geometries, while slow cells are hardly directed independently of thegeometry due to their tortuous swimming behavior. As a consequence, a rigorous characterization of eachmicro-swimmer motility is crucial for a proper micro-device optimization, using the largest amount of dataavailable, and automatically. Even more, due to the clear differences between fast and slow choanoflagellatesrectification results, an efficient micro-sorter device was fabricated, obtaining a good agreement between theoryand experiments [Miño et al, preprint].