Abstract
Simple polyembryony – where a single gametophyte produces multiple embryos with different sires but the same maternal haplotype – is common in conifers, ferns, horsetails and other vascular plants. Polyembryony could be favored as a mechanism of reproductive compensation, providing a backup for inviable embryos, or as a mechanism of embryo competition and eliminating plants with low fitness, perhaps acting as a mechanism of Self-Incompatibility (SI). However as the evolution of polyembryony from monoembryony has not been modeled these long standing verbal models have not been evaluated. We develop an infinite-site, forward population genetics model to test how these factors can favor the evolution of polyembryony, and how these underlying benefits of polyembryony shape the genetic load under a range of selfing rates, dominance, and selection coefficients. We find that the benefit of reproductive compensation strongly favors the evolution of polyembryony, while the benefits of embryo competition are much weaker. Importantly, when embryo competition favors the evolution of polyembryony it increases embryo competitiveness, but does not act as an SI mechanism, as it does not effectively trade low-fitness selfed offspring for high fitness outcrossed offspring. We find that the impact of polyembryony on the genetic load depends on its function – increasing the embryo load when acting as a mechanism of embryo compensation and decreasing the embryo load when acting as a mechanism of competition.
Competing Interest Statement
The authors have declared no competing interest.