Aspectos da evolução e da quebra da distilia em espécies de Psychotria L. e Palicourea (Aubl) (Rubiaceae)

Abstract

Flowering plants have several mating strategies. Distyly is one these breeding strategies, in which, plants present two floral morphs that occurs separately in a balanced ratio in each plant population. Stamens and stigmas of these floral morphs have reciprocal heights among them, beyond that, that is also a heteromorphic system of incompatibility that interrupts the growth of pollen tubes coming from self-pollinations or intramorph pollinations. This breeding system strategy is considered as a specialized mechanism for cross-pollination in plants. But, there are evolutionary transitions in this breeding system, like the loss of one of the floral morphs and absence of spatial separation of the sexual organs in the flower, called homostyly. In many plant groups there were studies about the evolutionary pathways of these transitions and what the effects in reproduction after distyly breakdown. In this thesis, we studied distyly and its breakdown in the plant genera with the greatest number of species presenting distyly, Psychotria L. e Palicourea Aubl. The study used phylogenetic reconstruction of distyly and its variations in species of both genera and either investigated the phenotypic selection in floral traits, the pollination imprecision in species and populations with distyly and transitions to other breeding systems. We further test if floral integration present effect in pollination imprecision in populations with distyly and its breakdown towards other breeding strategies. The studied showed that distyly is ancestral to the diversification of Psychotria and Palicourea genera. There was independent evolution of the transitions derived from distyly as monomorphism, homostyly, monoecy and dioecy. Due distyly ancestrally in these species groups it was not possible to infer any of the models proposed for the evolution of distyly in plants. The evolutionary transitions were reported in species with occurrence in island or in populations in isolated habitats, indicating the importance of founder effects in the evolution and establishment of species and populations with distyly breakdown. The corolla morphology was a better predictor than herkogamy (spatial separation od sexual organs) for a high female fitness in either distylous Psychotria trichophoroides and in the monomorphic species, Psychotria prunifolia. At the interspecific level, our study showed that precision in pollination is similar in both the species. Furthermore, the phenotypic integration of the species with distyly was higher than the monomorphic one. But, at the intraspecific level, populations with distyly presented higher pollination precision than the monomorphic populations of Psychotria carthagenensis and similar proportion of short and long-tongued pollinators. The phenotypic integration also was higher in flowers of the distylous populations than in the populations with monomorphism and there was a strong effect of the integration of the floral phenotype in the pollination precision in P. carthagenensis. The evolutionary breeding system transitions in Psychotria and Palicourea species seems to be more linked to local ecological pressures rather to differences in morphology of pollinators, and, represent the flexibility of adaptation of species of these genera in habitats that favours selfing. However, at the population level, distyly is a strategy that promotes high pollination precision, but, species with monomorphism can be as efficient in cross-pollination as species presenting distyly.