title: Coalescing red algae exhibit noninvasive, reversible chimerism.
abstract: Chimerism is produced by the somatic fusion of two or more genetically distinct conspecific individuals. In animals, the main cost of fusion is competition between genetically different cell lineages and the probability of original cell line replacement by more competitive invasive lines, which limits its natural frequency (3%-5%). In red and brown seaweeds, chimerism is widespread (27%-53%), seemingly without the negative outcomes described for animals. The rigidity of cell walls in macroalgae prevents cell motility and invasions. In addition, in moving waters, most somatic fusions involve the holdfast. Histological observations in laboratory-built bicolor macroalgal chimeras indicated that upright axes emerge from the base of plants by proliferation and vertical growth of discrete cell groups that include one or just a few of the cell lineages occurring in the holdfasts. Laboratory experiments showed growth competition between cell lineages, thus explaining lineage segregation during growth along originally chimeric erect axes. Genotyping of the axes showed more heterogeneous tissues basally, but apically more homogeneous ones, generating a vertical gradient of allele abundance and diversity. The few chimeric primary branches produced, eventually became homogenous after repeated branching. Therefore, coalescing macroagae exhibit a unique pattern of post-fusion growth, with the capacity to reverse chimerism. This pattern is significantly different from those in animals and land plants, suggesting chimerism is a biologically heterogeneous concept.
authors.affiliation: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Alameda 340, Santiago, Santiago, 8331150, Chile.
authors.forename: Bernabé
authors.initials: B
authors.lastname: Santelices
authors.affiliation: Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Casilla 653, Las Palmeras 3425, Ñuñoa, Santiago, 7800024, Chile.
authors.forename: Alejandra V
authors.initials: AV
authors.lastname: González
authors.affiliation: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Alameda 340, Santiago, Santiago, 8331150, Chile.
authors.forename: Jessica
authors.initials: J
authors.lastname: Beltrán
authors.affiliation: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Alameda 340, Santiago, Santiago, 8331150, Chile.
authors.forename: Verónica
authors.initials: V
authors.lastname: Flores
mesh_terms: D019070:Cell Lineage; D046528:Chimerism; D005787:Gene Frequency; D000461:Rhodophyta / Q000235:genetics* / Q000254:growth & development*; D012624:Seaweed / Q000235:genetics / Q000254:growth & development
keywords: cell competition; cell lineage segregation; chimerism; coalescence; upright axes formation