POPULATION STUDIES IN PREDOMINANTLY SELF-POLLINATED SPECIES. VIII. GENETIC VARIABILITY IN THE FESTUCA MICROSTACHYS COMPLEX.

Abstract

Recent quantitative studies of autogamous plants have provided increasing evidence that a low level of outcrossing can have effects on the genetic organization of populations that is out of all proportion to its frequency (reviews in Allard and Hansche, 1964; Allard, 1965). Quantitative data indicate that very low rates of outcrossing in populations can lead to a sharing of the common gene pool to an extent that such populations have integrated genetic structures with many features similar to those of freely intermating Mendelian populations. Quantitative data on rates of outcrossing and other relevant parameters of populational variability are, however, limited to a few species in which the rate of outcrossing is one percent or more and information about species in which outcrossing is an infrequent event is largely observational and subjective. It is consequently not clear just how low intrapopulational gene flow can fall before a species loses all semblance of genetic organization and its population structure becomes largely a matter of ecological interactions among reproductively independent arrays of familial isolates. A search for plant materials which would be suitable for study of population structure in heavily inbreeding species led to the selection for this purpose of a characteristic and prevalent element of the vegetation of California, a group of eight species of slender annual grasses which can