THE EVOLUTION OF AUTOGAMY IN SPECIES OF THE MUSTARD GENUS LEAVENWORTHIA.

摘要: In about 80% of all species hermaphroditic flowering plants the pollen is incapable germinating on styles flowers that produce it, a condition known as selfincompatibility (Fryxell, 1960). The genetic control usually simple, one-locus, and multiallelic (Lewis, 1954) although more complex two-locus systems are (Lundquist, 1975). number incompatibility mechanism has been shut off by dominant mutation. These capable self-fertilization. However, self-compatibility does not lead inevitably to self-pollination, various degrees selfing outcrossing can take place (Stebbins, 1957). general consensus 1954; Fryxell, 1960; Stebbins, 1957) self-incompatibility primitive in Angiosperms secondary derived. Since autogamy evolved repeatedly, evolutionary consequences interest. Autogamy tends increase inbreeding, most normally cross-fertilized plants, inbreeding decrease vigor seed production (Darwin, 1877; Consequently it valid ask why some do become autogamous spite apparently deleterious effects resulting from inbreeding. It suspected losses due must be compensated for other way. To test existence such tradeoffs, group closely related taxa, growing similar environments required. One small genus Leavenworthia (Rollins, 1963). A single polyploid; remaining six diploid divided into two groups basis chromosome number. with 11 pairs chromosomes formed L. alabamica crassa, which have both self-incompatible selfcompatible populations 1963; Lloyd, 1965) derived self-compatible, largely selfed species, exigua. 15 composed one stylosa, torulosa uniflora. seventh polyploid aurea (n = 24), restricted its distribution local eastern Texas southeastern Oklahoma (Fig. 1). All grow calcareous outcrops, locally cedar glades. crassa glades northern Alabama; stylosa found Central Tennessee, while highly wider distribution. exigua north central Alabama, northwestern Georgia, Kentucky; uniflora grows Alabama southern Ohio Indiana, Missouri Arkansas. Species limestone outcrops occasionally adjacent agricultural fields. kinds tradeoffs expected occur result changes breeding system involve structure population, pollination mechanism, set efficiency, growth pattern, size populations. Consequently, present study focused these biological aspects each aspect we contrasted behavior an in-depth very