The lead author of the recent Evolution paper has posted a commentary on kudos that includes some ideas not included in the paper:

The life cycle and ecology of volvocine algae may be key to understanding the long-term persistence of self-fertilization. First, selfing in homothallic volvocine algae is facultative; in a genetically diverse population, most matings will be between genetically distinct strains. Second, volvocine algae have a haploid-dominant life cycle with a metabolically active, multicellular haploid stage and a dormant, unicellular diploid stage. Inbreeding depression may thus be less important than in species with diploid-dominant life cycles. Finally, the dormant diploid stage allows volvocine algae to overwinter, meaning that the ability to self-fertilize is crucial for the survival of colonists to new ponds. Thus facultative selfing might provide volvocine algae with the benefits of outcrossing (when other genotypes are around) without the cost of potentially being unable to find a mate.

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Ancestral character states
Ancestral state reconstruction of selfing (left) and monoecy (right). Left, the evolution of outcrossing (black) and selfing (green). Right, the evolution of dioecy (black, for this analysis, outcrossing heterothallic species were treated as dioecious) and monoecy (blue).

Hanschen ER, Herron MD, Wiens JJ, Nozaki H, Michod RE. 2017. Repeated evolution and reversibility of self-fertilization in the volvocine green algae. Evolution (pdf)


The Herron Lab at Georgia Tech studies various aspects of the evolutionary origins of multicellularity through a combination of experimental, theoretical, and comparative approaches. Our main model systems are the volvocine algae (Volvox and kin) and their close unicellular relative, Chlamydomonas reinhardtii.