Evolution of mating types in finite populations: The precarious advantage of being rare

• Published in: Journal of evolutionary biology Vol. 32; no. 11; pp. 1290 - 1299
• Main Authors: Czuppon, Peter, Rogers, David W.
• Format: Journal Article
• Language: English
• Published: Switzerland Blackwell Publishing Ltd 01.11.2019; Wiley
• Subjects: Advantages; balancing selection; Drift; finite population; genetic drift; Incompatibility; Life Sciences; Mating; Mating types; Mutants; Population; Populations; Reproduction (biology); Risk assessment; self‐incompatibility; Stochasticity; self-incompatibility; balancing selection; genetic drift; mating types; finite population
• ISSN: 1010-061X; 1420-9101
• DOI: 10.1111/jeb.13528

Sexually reproducing populations with self‐incompatibility bear the cost of limiting potential mates to individuals of a different type. Rare mating types escape this cost since they are unlikely to encounter incompatible partners, leading to the deterministic prediction of continuous invasion by new mutants and an ever‐increasing number of types. However, rare types are also at an increased risk of being lost by random drift. Calculating the number of mating types that a population can maintain requires consideration of both the deterministic advantages and the stochastic risks. By comparing the relative importance of selection and drift, we show that a population of size N can maintain a maximum of approximately N1/3 mating types for intermediate population sizes, whereas for large N, we derive a formal estimate. Although the number of mating types in a population is quite stable, the rare‐type advantage promotes turnover of types. We derive explicit formulas for both the invasion and turnover probabilities in finite populations. We investigate the number of self‐incompatible mating types in a finite population under a neutral model. This invasion‐extinction balance is, for low to intermediate population sizes N, well approximated by N1/3.