Molecular genetic variation in the chloroplast and mitochondria is commonly used to discern patterns of population structure, gene flow, and phylogeography is plant species. However, few studies have questioned whether associations between the markers and components of fitness through seed may differentially influence cytoplasmic haplotypes. We studied associations between mitochondrial DNA haplotype (mtDNA), chloroplast DNA haplotype (cpDNA), gender, and some components of fitness through seed in one population of the gynodioecious plant Silene vulgaris. All individuals in the population were sampled for mtDNA and cpDNA RFLP haplotypes, gender (female or hermaprhodite), fruit number, fruit set, seeds/fruit and seed germination. All individuals fell into one of two cytoplasmic haplotype categories: 31 individuals carried haplotype f and 43 individuals carried haplotype g. Gender was not randomly associated with haplotype: individuals with haplotype f included a significantly lower proportion of females than individuals with haplotype g. Haplotypes did not differ significantly with regard to average fruit number. However, individuals with haplotype g had higher fruit set and produced more seeds per fruit than individuals with haplotype f and seeds from individuals with haplotype f had significantly higher germination rates than those from individuals with haplotype g. Other studies have shown that females generally have higher fitness through seed than hermaphrodites, but in this study fitness differences between haplotypes could not be predicted from differences in haplotype-specific sex ratio alone. These results indicate the possibility that there are different categorical types of females and hermaphrodites within gynodioecious populations that differ in how they gain fitness. Such patterns may result from fitness difference associated with different gender determination genes. This study suggests how hitchhiking selection between cytoplasmic genes affecting gender and other co-transmitted genomes may compromise the assumptions of selective neutrality of genetic markers in the chloroplast or mitochondrial genomes.

Key words: cpDNA, cytoplasmic male sterility, fitness, gynodioecy, mtDNA, selection