I am interested in studying sex ratio evolution and have chosen a gynodioecious annual plant, Nemophila menziesii (Hydrophyllaceae) to do this.  N. menziesii is hermaphroditic throughout most of its range in California and Oregon, however around the San Francisco Bay Area, populations with female individuals occur.  Female frequencies range from 0 to 53% and can vary considerably over distances as short as 100m.  In addition, female frequencies vary through time.

 Sex is inherited in N. menziesii through a combination of nuclear and cytoplasmic genes.  Male sterility is coded for by genes located in the cytoplasm.   Cytoplasmic genes are inherited maternally, only through ovules thus the loss of pollen production does not decrease their fitness.  Nuclear genes, however, gain fitness through both pollen and ovules thus male sterility reduces their fitness.  One might expect to see selection for nuclear alleles that restore male fertility and these nuclear restorer alleles are in fact found in all plants with cytoplasmic male sterility.  This differential inheritance between mitochondrial and nuclear genomes sets up a conflict between them, the result of which is gynodioecy and variable sex ratios.

My research is examining the population genetics of both cytotypes and nuclear restorers in a set of populations just north of San Francisco.  These data will be used to examine the extent to which gene flow events may be maintaining the presence of female individuals once nuclear restorer alleles for that cytotype have been introduced.

 Finally, I am examining whether a hybridization event may be the cause of the regionally high female frequencies in the Bay Area.