The evolution of non-self recognition self incompatability

The evolution of biological recognition systems has long fascinated biologists. To avoid inbreeding, many plants have evolved recognition systems that prevent self-fertilization and mating among relatives. This raises the question of how plants recognize their own and foreign pollen? For snapdragons (Antirrhinum), when pollen arrives on a flower there is a molecular mechanism where fertilization by pollen from a genetically different individual is possible only because it can recognize all other genetic types in the population, but not its own (non-self recognition). Self-incompatibility systems are unique in that this part of the genome (locus) has amongst the highest genetic diversity recorded. Diversity of mating types is maintained by balancing selection, where a rare type has a mating advantage. Yet, an added complication in recognition system evolution is that both components here, male and female-determining genes need to change to create a new functional type. This raises the question: how, and under what conditions, do new mating types evolve? The goal of this study is to combine population genetics theory with molecular genomics to investigate the diversity of genes that control the male component of non-self recognition self- incompatibility, and to examine how new mating types may evolve. To do this, I will first use the well-characterized snapdragon (Antirrhinum) system to study the diversity and structure of SLF (male-component) genes, both within and between species. Here, using knowledge of the location of the self-incompatibility locus (from the reference genome) and sequences of the 40 known SLF genes I will answer the questions: (i) are SLF haplotypes (the set of SLF genes) more similar within, compared to between species? And (ii) is the structure of the SLF genomic region, and the SLF genes themselves, more different when comparing haplotypes from species that are more distantly related. For this I will analyze whole genome data from 18 Antirrhinum species. For the second part of this project I will extend current theoretical models to examine if population structure (restricted migration among populations) and genetic exchange (mixing of SLF genes during mating) facilitate the evolution of new mating types. This is a key question, because previous models have not been able to explain the high number of mating types observed in nature. I predict that greater population structure and the exchange of SLF genes will increase the number of mating types that can evolve. By combining genomics and theoretical modeling, this project will provide new insights into the evolution of non-self recognition self-incompatibility systems. More broadly, this will illustrate how genomic variation and population structure can interact to influence the evolution of a complex adaptation that is widespread in flowering plants.