The Strategy of the Red Algal Life History

The unusual triphasic life history of the red algae is explained as an evolutionary compensation related to the lack of motility of gametes in the division and the presumed relatively infrequent occurrence of syngamy among their ancestors. The essential element of this life history is the retention, nurture, and replication of the zygote by the gametophyte to form the carposporophyte. Multiple diploid spores are then subsequently released into the environment to produce multicellular diploid plants, many cells of which divide meiotically when forming spores to yield a potentially great diversity of genotypes from a single original zygote. In other algal divisions syngamy is facilitated by the presence of flagellated gametes and a higher percentage of zygotes can be expected per gamete produced. Parallels to the red algal life history are seen in the rust fungi, which lack flagellated gametes, and in the Embryophyta, in which the terrestrial environment places limitations on successful zygote formation.