Does self-fertilization rescue populations or increase the risk of extinction?

Pierre-Oliver Cheptou examines two seemingly contradictory findings. Over the last 10 years, well-established patterns of evolution have emerged. First, experimental studies have shown that self-fertilization is likely to evolve in a few generations (microevolution). This is as a response to rapid environmental change. (e.g. pollinator decline), eventually rescuing a population. Yet, phylogenetic studies have demonstrated that repeated evolution towards self-fertilization (macroevolution) leads to a higher risk of lineage extinction. In the long-term evolving self-fertilization is likely to be disadvantageous.

Phylogenetic relationships in the Solanaceae species
Phylogenetic relationships in the Solanaceae species (356 species). See Cheptou 2019 for details.

In either case – the short-term or long-term evolution of self-fertilization (selfing) – these findings show that a mating system is not neutral with respect to population or lineage persistence. They also suggest that selfing can have contrasting effects depending on time scale. This raises the question of whether mating system evolution can rescue populations facing environmental change. In his review, Cheptou analyzes empirical and theoretical evidence of the direct and indirect effects of mating systems on population demography and lineage persistence . He also developed a simple theoretical evolutionary rescue model to investigate the potential for evolutionary rescue through selfing.

Demographic studies show a short-term advantage of selfing provided by reproductive assurance, but a long-term disadvantage for selfing lineages, suggesting indirect genomic consequences of selfing (e.g. mutation load and lower adaptability). But, his theoretical evolutionary rescue model found that even in the short term, while mating system evolution can lead to evolutionary rescue, it can also lead to evolutionary suicide, due to the inherent frequency-dependent selection of mating system traits. These findings point to the importance of analysing the demographic consequences of self-fertilization in order to predict the effect of selfing on population persistence as well as take into account the indirect genomic consequences of selfing.

Further reading

Cheptou, P.-O. (2018). Does the evolution of self-fertilization rescue populations or increase the risk of extinction? Annals of Botany, 123(2), 337–345. https://doi.org/10.1093/aob/mcy144