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Browsing by Author "Harkness, Alexander"

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    Theoretical evolutionary genetics of plant mating system and self-incompatibility
    (2020-12) Harkness, Alexander
    The mating system of a diploid eukaryote is an outcome of intragenomic coevolution. Close relatives are more likely to share recessive deleterious mutations at many locations, so an allele at another locus that reduces the probability of inbreeding will increase offspring’s expected fitness. Self-incompatibility in flowering plants, which acts through a polymorphic locus (an S-locus) that rejects pollen when pollen and pistil haplotypes match, is a particularly old and widespread inbreeding avoidance adaptation that has persisted through long-term balancing selection among different S-locus haplotypes (S-haplotypes). Intragenomic coevolution occurs between the individual elements of the S-locus: those expressed in pollen and those expressed in pistils. When intragenomic coevolution is disturbed, selection on mating system or on particular mating system adaptations is shifted and the population may adapt in new ways. In this thesis, the theoretical consequences of three disturbances to the intragenomic coevolution of mating system in flowering plants are determined. First, it is shown that isolation of the genetic load in separate inbreeding populations produces a transitory benefit upon secondary contact to a mutation promoting outcrossing, but that this benefit evaporates too rapidly as the populations reassimilate to favor the evolution of greater outcrossing consistently. Second, it is shown that, under the taxonomically widespread ribonuclease-based self-incompatibility system, the evolution of a novel S-haplotype greatly disturbs inter-haplotype coevolution, and may either lead to coexistence of all haplotypes (diversification) or extinction of multiple haplotypes (collapse) in a rescue-like process. Third, it is shown that biased patterns of pollen rejection form between non-coevolved S-haplotypes from isolated populations, which may favor the introgression of some haplotypes, prevent introgression of others, and cause some to be lost by swamping introgression.