Breeding systems in a temperate mediterranean-type climate montane sclerophyllous forest in central Chile

Abstract

The frequency of dioecy in the predominantly biotically-pollinated native flora of a temperate montane sclerophyllous forest in central Chile, 33°S, is determined. Experimental crosses and other tests were performed on a taxonomically diverse set of annual herbs, perennial herbs and woody species to detect genetic self-incompatibility, spontaneous selfing capacity and obligate agamospermy. The overall frequency of dioecy in the community is 9%. Dioecy is unequally represented among life-forms, increasing in frequency with greater longevity: 0% in annual herbs; 20 in perennial herbs; 17% in shrubs; 57% in trees. Thirty-eight percent of 37 hermaphrodite species proved to be genetically self-incompatible. Self-incompatibility, like dioecy, increases in frequency with longevity: 0% in annual herbs; 50% in perennial herbs; 80% in shrubs. The self-compatible species showed a wide range of breeding habits from facultative outcrossing to strong autogamy. However, in most self-compatible species hand self-pollination increased fruit and seed set over spontaneous selfing. Obligate agamospermy was not detected among hermaphrodite species. Absolute and relative fecundity were strongly correlated with the degree of compatibility. However, reduced fecundity in obligate outbreeding species could not be unequivocally attributed to pollinator limitation. For equivalent life-forms, the montane sclerophyllous forest exhibits proportionately more obligate outbreeding species than some tropical forests and other temperate communities. The strong tendency for obligate outcrossing in the Chilean community is seen as a result of interplay between life-history constraints and the intense abiotic and biotic pressures that are characteristic of the mediterranean-type climate community.