Estudos biossistematicos em especies de Hoffmannseggella H.G. Jones (Orchidaceae: Laeliinae) ocorrentes em complexos rupestres de altitude / Biosystematic studies in Hoffmannseggella H.G. Jones (Orchidaceae: Laeliinae) occuring in altitude rocky complexes of Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

A biosystematic study of the neotropical and Brazilian endemic genus Hoffmannseggella H. G. Jones was carried out. This genus is characterized by rupiculous habit, with varied-contrasting flowers colors. These species are distributed at high altitude rocky complexes, mainly in the Southeast (MG, RJ and ES) and Northeast (BA). The geographic distribution patterns of 34 Hoffmannseggella and three Dungsia species by GIS techniques were described. The results point to four sub-sets of species groups: Chapada Diamantina - BA, Northern and Southern part of Central area of the Espinhaço Range – MG and rocky complexes of RJ/ES. Parsimony analysis of endemicity and ecological modeling indicated 12 priority areas for conservation and more three complementary areas to guarantee the species survival for a long time. The results of molecular dating are presented, with emphasis on Hoffmannseggella, including related genera, in a historical-evolutive perspective. The most probable biogeographic and historical scenario in Laeliinae points to the origin and confinement of basal species in Central America in the Miocene, with posterior irradiation of derivated groups to South America, through a partial link by islands in “Proto Central America”. The main cladogenesis events in Hoffmannseggella are not associated with specific areas, but happen in multiple events associated to the expansion and retraction of open vegetation in the Plio-Pleistocene. Floral biology and pollination ecology studies were carried out in eight Hoffmannseggella species, with attention to the reproductive isolation mechanisms between sincronopatric species. Hoffmannseggella species are pollinated by small bees (Hymenoptera) of different families, with unspecific and deceit based pollination systems that discredit previous suppositions that characterized Hoffmannseggella as ornithophilous. Breeding system studies of 13 species and 36 different populations revealed that most species are self-compatible, but the same species can present different breeding systems depending on the population. The break up of self-incompatibility in some species is associated to polyploidy, and this phenomenon is relatively frequent in Angiosperms, but had been never described in orchids. Selfcompatibility in polyploid species can confer advantages in establishment of polyploid lineages. A review of chromosome numbers in Hoffmannseggella, show new counts for 12 species and two natural hybrids in 24 different populations, with emphasis in the importance of polyploidy for the evolution of this group. Some species presented different cytotypes, and this is discussed in a cytogeographic and evolutive perspective, with emphasis on the main factors related with establishment of polyploid complexes. Polyploidy is a recent phenomenon in Hoffmannseggella, but can appear independently many times in its evolutionary history. A new species, H. viridiflora, is described and morphologically related to species with short racemes, yellow and smaller flowers, occurring at the Diamantina Plateau - MG. Finally, we present a general biosystematic and conservationist view, which points the main problems associated with the maintenance of natural areas with high diversity of Hoffmannseggella species.

ASSUNTO(S)

pollination polinização datação molecular reprodução chromosome numbers molecular dating biogeography biogeografia

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