The loss of self‐incompatibility in a range expansion

• Published in: Journal of evolutionary biology 2020-09, Vol.33 (9), p.1235-1244
• Main Authors: Encinas‐Viso, Francisco, Young, Andrew G., Pannell, John R.
• Format: Article
• Language: English
• Subjects: Animal behavior; Baker's law; colonization; dispersal; Evolution; Expansion; Genetic load; Inbreeding; Inbreeding depression; Incompatibility; Loci; metapopulation; Metapopulations; migration; Pollinators; Range extension; Recombination; reproductive assurance; selfing; self‐compatibility
• ISSN: 1010-061X; 1420-9101
• DOI: 10.1111/jeb.13665

It is commonly observed that plant species' range margins are enriched for increased selfing rates and, in otherwise self‐incompatible species, for self‐compatibility (SC). This has often been attributed to a response to selection under mate and/or pollinator limitation. However, range expansion can also cause reduced inbreeding depression, and this could facilitate the evolution of selfing in the absence of mate or pollinator limitation. Here, we explore this idea using spatially explicit individual‐based simulations of a range expansion, in which inbreeding depression, variation in self‐incompatibility (SI), and mate availability evolve. Under a wide range of conditions, the simulated range expansion brought about the evolution of selfing after the loss of SI in range‐marginal populations. Under conditions of high recombination between the self‐incompatibility locus (S‐locus) and viability loci, SC remained marginal in the expanded metapopulation and could not invade the range core, which remained self‐incompatible. In contrast, under low recombination and migration rates, SC was frequently able to displace SI in the range core by maintaining its association with a genomic background with purged genetic load. We conclude that the evolution of inbreeding depression during a range expansion promotes the evolution of SC at range margins, especially under high rates of recombination.‬ Range expansions create conditions (low inbreeding depression and mate availability) for the breakdown of self‐incompatibility (SI). More specifically, we show that low recombination and migration rates facilitate the transition to selfing in range edge populations, while the opposite (high recombination and migration) favours the maintenance of SI and under certain conditions the coexistence of SI and selfing.