Fig 1.
Experimental set-up and slug versus cell size.
(A) Experimental set-up: on the left, cells were placed at 1 cm from the periphery of the Petri dish (gray ring) at the opposite side from the light source. On the right, cells in dark condition were inoculated into the center of the Petri dish. Dashed lines represent region of interest where slugs migrated. (B) Comparison between slug and cell size: fluorescence imaging of a slug composed of 1% fluorescent GFP cells (left) and vegetative cells (right).
Fig 2.
Phototaxis is an emergent property of multicellularity.
Trajectories (centered from Eq (1)) and polar representations of start-end directions (from Eq (2)) of slugs (A) and cells (B and C) when exposed to light (orange) or in the dark (violet). Slug migration showed no preferential direction in the dark but was oriented towards the light source under lateral illumination (A). Vegetative cells (B) and cells from dis-aggregated slugs (C) showed no preferential direction whether in the dark or exposed to lateral light. Directional statistical analysis were computed from Eq (13) for r values and Rayleigh test for uniform angles distribution from Eq (14).
Fig 3.
Phototaxis efficiency as a function of slug size:
(A) Schematic representation of parameters: start-end direction estimated from Eq (2) (a) and instantaneous direction from Eq (3) (b). Distribution of start-end directions (B-a) and distribution of instantaneous directions relative to the light source direction (B-b) for 6 intervals of slug sizes (cell number) under lateral illumination (orange) or in the dark (violet). Corresponding phototaxis efficiency (C) estimated from Eq (5). Points in C were fitted with a polynomial function of degree 4. Phototaxis efficiency increases gradually with slug size.