Population dynamics of the gynodioecious Boutelouachondrosioides (Poaceae)

Abstract

This dissertation investigated the evolution and ecology of male sterility in the gynodioecious Bouteloua chondrosioides (Poaceae) by studying the distribution, inheritance, phenotypes of male sterility, mitochondrial DNA polymorphisms, and the distribution and effect polyploidy has on sex type expression in B. chondrosioides. B. chondrosioides has two male sterile types, one of which is described for the first time in this dissertation. Field studies determined that the proportion of male sterility was highly variable among populations and non-randomly distributed within populations. Investigations of the progeny of individuals of known sex type rejected models of simple nuclear recessive and dominant inheritance of male sterility. Examination of characters that may affect reproduction demonstrated that there were few significant reproductive differences explaining the maintenance of the two male sterile forms. In order to investigate if male sterility is due to cytoplasmic factors, mitochondrial DNA restriction fragment length polymorphisms were examined to determine if there were correlations between unique restriction fragment patterns and male sterile forms. These studies demonstrated that some, but not all, male sterile individuals do have unique mitochondrial restriction fragments. In addition to these investigations, the distribution of polyploidy was characterized and investigations performed to determine if there are correlations between sex type and ploidy level and if polyploidy has evolved once or multiple times in B. chondrosioides. Flow cytometry resulted in data that demonstrated no correlation between male sterility and ploidy level, and that while most populations are either only diploid or tetraploid, some populations had both diploid and polyploid individuals. The examination of the relationships of cpDNA sequences from individuals of known ploidy level demonstrated that polyploidy appears to have originated and established more than once in the history of B. chondrosioides. The results from these three studies exhibit patterns that are in accord with the hypothesis that male sterility in B. chondrosioides is due to cytoplasmic male sterility.