Female frequencies and fitness components between sex phenotypes among gynodioecious populations of the colonizing species Trifolium hirtum All. in California

Abstract

Male sterility has been recently discovered in Californian populations of rose clover (Trifolium hirtum). This study describes the frequency distribution of male sterility in Turkish and Californian populations, and compares fitness components of hermaphrodites and females. As male-steriles were found in Turkey, it is likely that they were introduced to California during the 1940's with the original material derived from Turkey. The spread of male-sterile genotypes in California has given rise to an asymmetrical frequency distribution of male sterility with positive skewness. The frequency of females has not exceeded fifty percent and it appears to be temporally stable in most of the Californian populations. The hypothesis that female frequencies and fitness differences between phenotypes are correlated was tested by comparing sex phenotypes in seven populations with contrasting levels of male sterility. The analysis of those populations showed no evidence for such a correlation as no significant differences were found between sex phenotypes for fecundity and seed germination. The hypothesis that females are maintained due to fitness differences in the progeny of hermaphrodites and females was experimentally tested in the population with maximum frequency of male-steriles. The results showed no significant differences in the demographic performance of the progenies of hermaphrodites and females. The present results are discussed in terms of the possible mechanism of maintenance of gynodioecy in rose clover.

Keywords: Colonizing species; Ecological genetics; Gynodioccy; Sex ratio; Trifolium hirtum.