ESTIMATING LONG-TERM MATING SYSTEMS USING DNA-SEQUENCES

Plant mating systems often involve a mixture of self fertilizations an d outcross fertilizations. The degree of selfing has a large impact on the genetic composition of natural populations and on the evolution o f the mating system itself in response to such factors as inbreeding d epression. This paper describes a means of estimating the long-term ra te of self-fertilization from samples of alleles taken from individual s in a population. Use is made of the genealogy of pairs of alleles at a locus within individuals and pairs between individuals. The degree of selfing is closely related to the extent to which the number of nuc leotide sites differing within an individual is reduced relative to th e number differing between individuals. Importantly, the estimate of l ong-term selfing is largely independent of population size and is not affected by historical fluctuations in population size; instead it res ponds directly to the mating system itself. The approach outlined here is most appropriate to evolutionary problems in which the long-term n ature of the mating system is of interest, such as to determine the re lationship between prior inbreeding and inbreeding depression.