Dynamics of Somatic Cell-Lineage Competition in Chimeras of Hydractinia symbiolongicarpus (Cnidaria: Hydrozoa)

• Main Authors: Ryan S. Schwarz, Luis F. Cadavid
• Format: Article
• Language: English
• Published: Universidad Nacional de Colombia 2007-08-01
• Series: Acta Biológica Colombiana
• Subjects: Orreconocimiento; Hydractinia; Unidades de Selección; Competición; Quimeras
• Online Access: https://revistas.unal.edu.co/index.php/actabiol/article/view/27234
• ISSN: 0120-548X; 1900-1649

Sessile colonial invertebrates often fuse with conspecifics to form chimeras. Chimerism represents an unequivocal instance of withinindividual selection where genetically different celllineages compete for representation in the somatic and gametic pools. We analyzed temporal and spatial variations in somatic celllineage composition of laboratoryestablished chimeras of the hydroid Hydractinia symbiolongicarpus (Cnidaria: Hydrozoa). Using three clones with different allotypic specificities (i.e., two rejecting one another but fusing with a third one), we established two classes of twoway chimeras, a single threeway chimera class, and an incompatible interaction as control. Chimeras were sampled at five time intervals for a year. Celllineages in samples were identified by polyp fusibility assays against tester colonies of known fusibility. The cell lineages composing the chimeras showed a differential competitive ability, with one of them representing close to 80% by the end of the study. Rare celllineages stabilized at low frequencies but preserved their ability to gain somatic representation and to colonize distant parts of the chimera. This behavior characterizes cell parasites. As a consequence of the reproductive plasticity of most colonial invertebrates, celllineage variability may be transmitted to the offspring both sexually and asexually. Successful somatic competitors are expected to be preferentially transmitted asexually, whereas cell parasites would be preferentially transmitted sexually.