Investigation of Inbreeding Depression in <i>Boechera stricta</i> Fitness

Abstract

Maintaining high levels of self-fertilization within a population increases homozygosity, exposes deleterious alleles, and may cause inbreeding depression. Yet, many species of flowering plants have evolved to self-fertilize a majority of the time. Often, self-fertilization is favored over outcrossing when small populations experience harsh or stressful environments. Self-compatibility may evolve after a founder event or when natural selection favors high reproductive assurance, such as when there is limited pollinator activity. When this occurs, selfing syndrome, the reduction of petal size and pollen production, may follow. Conversely, natural selection may remove deleterious alleles from highly self-fertilizing plants, allowing for combinations of locally-adapted alleles to arise. As a result some species may show no evidence of inbreeding depression, and in fact may have decreased fitness due to loss of locally co-adapted allele combinations following outcrossing. In ​Boechera stricta ​(Brassicaceae), a highly selfing perennial wildflower, the relative fitness costs of inbreeding vs. outcrossing are not characterized. In order to test for inbreeding depression and signs of selfing syndrome in Boechera stricta, ​I performed​ ​controlled crosses and and measured trait variation among selfed and outcrossed genotypes in a common garden experiment. Our results suggest a trend that more inbred populations of ​Boechera stricta ​may have higher fitness, such as larger fruit size, than outbred populations. In addition, more inbred populations were observed to reach reproductive maturity and flower earlier than outbred populations.

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