Genetics and sex expression in Alaskan populations of Silene acaulis

Abstract

Gynodioecy, the coexistence of hermaphrodites and females within plant populations, is often caused by an interaction between maternally-inherited cytoplasmic male sterility (CMS) genes and nuclear male fertility restorer genes. Previous population studies have found cytoplasmic alleles associated with femaleness. We analyzed the spatial distributions of mitochondrial and chloroplast alleles and the sexual phenotype of individuals within five Alaskan populations of Silene acaulis. Sex ratios were variable between two mountain ranges in this study, possibly due to differences in the frequencies of CMS genes. Clustering of mitochondrial alleles, but not sex, was found within two populations at a scale <̲ 2 m. This result may be because maternally-inherited mitochondrial genes are locally spread through seed, but nuclear restorers are spread through pollen and seed. We also investigated sex ratios and CMS genes temporally and did not find patterns of changing sex ratios or mitotypes across size classes. This does not support the theory that females and the mitotypes they carry have been selected against over time, implying that female clusters were not broken-up due to pollen limitation. Patterns of mitochondrial and chloroplast alleles suggest either non-maternal inheritance of cytoplasmic markers or multiple reversals in the evolutionary history of cytoplasmic markers.