Fig. 6: Kin recognition constrains aggregation.
From: Clonal-aggregative multicellularity tuned by salinity in a choanoflagellate
a, The source location of C. flexa strains. b, The M44 and M60 splash pools (Exped-B). The dashed lines show the splash pool outlines. c, Phylogenomic tree of single-sheet-bottlenecked cultures (SSB) and single-cell bottlenecked clones of strains 1, 2 and 3. d–f, Fluorescently labelled cells of strain 1 readily aggregate with other cells of strain 1 (d) or with strain 3 (e) but less with strain 2 (f), indicating kin recognition. Scale bar, 20 μm. g, Quantification of kin recognition using a segregation index (s) based on the relative proportions of strains (P = 1.8 × 10−9, one-way ANOVA). s = 0 indicates no kin discrimination, and s = 1 indicates complete segregation (Methods and Supplementary Fig. 10c). n = 2 biological replicates, n = 2 technical replicates each (n = 530 sheets). h, The number of genes with high Ka/Ks regions (Ka/Ks > 2) for each pairwise strain comparison. i, The top 10 InterProScan domain annotations enriched in regions with Ka/Ks > 2 comparing strain 1 and strain 2. Statistical analysis was performed using the Fisher’s exact test. j, The number of non-synonymous substitutions in the candidate kin recognition locus FUN_000880, encoding a predicted cadherin, in all pairwise strain comparisons (top). Bottom, the Ka/Ks ratio along the FUN_000880 coding sequence (top row). The predicted domain architecture is shown (bottom row). non-syn., non-synonymous; TM, transmembrane domain; Cyt., cytoplasmic domain. k, The environmentally entrained life cycle of C. flexa. Multicellular sheets dominate at low salinity, under which clonal-aggregative multicellularity confers a feeding and growth advantage. Unicellular cysts dominate at high salinity, under which they have a survival advantage. Sheets undergo dissociation–encystation under evaporation. After refilling, cysts differentiate into solitary flagellates that engage in clonal-aggregative sheet reformation after refilling. The pink arrowheads show collar–collar contacts. The figure is related to Extended Data Fig. 9, Extended Data Table 1, Supplementary Figs. 9–11 and Supplementary Data 5 and 6.
