REPRODUCTIVE EFFORT IN DESERT VERSUS MEDITERRANEAN CRUCIFERS - THE ALLOGAMOUS ERUCARIA-ROSTRATA AND E-HISPANICA AND THE AUTOGAMOUS EROPHILA-MINIMA

Components of the total sexual investment of plants growing under medi terranean climatic and edaphic conditions were compared with those of plants growing in the desert, in the closely related allogamous specie s pair Erucaria hispanica and E. rostrata and in populations of the au togamous species Erophila minima. In all cases lower total investment was evident in the desert plants. Al the prezygotic phase it was expre ssed by (1) reduced production of flowers, (2) lower allocation to the production of male gametophytes and some floral organs; and (3) packa ging of more ovules per ovary. The ratio of reproductive:vegetative bi omass which was found to be greater in the desert plants and their low er pollen:ovule ratio are perhaps indicative of greater efficiency. Th eir smaller investment at the postzygotic phase was expressed in: (1) reduction in total numbers of fruits and seeds; (2) decrease in seed s ize and weight. Yet in the desert plants the number of seeds per total biomass was found to be significantly larger and fertility rates (see d-set per ovule, fruit-set per flower per plant) were equal to or grea ter than those in the mediterranean plants. The trends observed in thi s study in desert plants, which may result in more efficient exploitat ion of resources, are similar in the species involved, regardless of t heir breeding system - autogamous or allogamous.