Dissertation Research: Evolution of Female/Male Ratio in Gynodioecious Nemophila Menziesii

University Of California-Irvine, Irvine CA

Investigators

Abstract

0073550 Weller & Barr The appearance of females in hermaphroditic plant populations has been a puzzling evolutionary phenomenon because females would appear to suffer in gene transmission compared with hermaphrodites. Another puzzle is that female frequencies can vary considerably over short distances and time scales. In many species, sex is determined by an interaction between nuclear and cytoplasmic genes. One mechanism that has been proposed to explain female frequency variation is repeated gene flow of cytoplasmic male sterility (female-causing) and nuclear male fertility restoring (hermaphrodite-causing) genes and a conflict of interest between these two genomic subsets. This gene flow model will be tested with an annual plant, Nemophila menziesii, which shows considerable variation in female frequency. An alternative hypothesis to gene flow, the effect of females on hermaphrodite fitness and how that affects female frequency dynamics, will also be investigated. A third experiment is proposed to determine transmission genetics of nuclear restorer alleles. Finally, the role of hybridization leading to the appearance of females on a large geographic scale will be examined. Theoretical work has shown that genomic conflicts may be the cause of a large array of evolutionary phenomena. Cytoplasmic male sterility is one of the best studied genomic conflicts largely because of its use in agricultural hybrid seed production. However, outside of work on few model systems, the dynamics of genomic conflicts affecting sex ratios in natural systems has not been established. This study of Nemophila menziesii will test new models and tie in previous work with genomic conflict theory. The genetics of cytoplasmic male sterility will also be investigated. Finally, the regional sex ratio variation seen in N. menziesii is a unique feature that allows for an examination of large-scale sex ratio processes.