The mating system and genetic variability in natural populations of Collinsia heterophylla
Weil, J.; Allard, R.W.
Evolution 18(4): 515-525
ISSN/ISBN: 0014-3820 DOI: 10.2307/2406206
Genetic variability and mating system were investigated quantitatively in Collinsia heterophylla from 3 different localities in central California. Seed parents were chosen from 2 sites within each locality, and the progenies of these plants were grown in a replicated field planting at Davis, California. Individual plants were scored for 2 monogenic color characters and measured for 8 quantitative characters related to plant size and rate of development. Estimates of percentage of outcrossing based on the monogenic characters and occurrence of moderate inbreeding depression for the quantitative characters indicate that the species is predominantly outcrossing. Three sources of genetic variability for the quantitative characters could be distinguished and measured: differences between localities, differences between sites within localities, and plant-to-plant differences within sites. The means of localities were found to differ for all characters measured. The most striking differences were those involving mature plant size. For 7 of the quantitative characters, statistically significant differences were found between the means of progenies within sites. Estimates of the genetic variability within sites were made from the between progenies components of variance. The results confirm previous observations that substantial quantitative genetic variability exists in outbred plant populations. Distinct genetic differentiation between sites occurred in one of the localities. Ecological differences and genetic isolation between the sites suggested that this locality had the most favorable structure for such differentiation. For most characters the magnitude of the difference between the 2 sites of this locality was significant in comparison with both the differences between the means of the 3 localities and the magnitude of the genetic variation within sites. It thus appears that genetic differentiation over very short distances can contribute appreciably to both the genetic variability within one locality and the genetic variation observed over large geographical areas.