Generic delimitations and molecular phylogeny in Tillandsioideae

Research project P 13690 Generic delimitations and molecular phylogeny in Tillandsioideae Walter TILL 28.06.1999 Subfamily Tillandsioideae of the pineapple family (Bromeliaceae) is the largest of the three recognized subfamilies and is likely to be basal. 1100 species are currently assigned to genere which are quite homogenoeus in Alcantarea, Catopsis, Glomeropitcairnia, Racinaea, and Werauhia but which are doubtlessly paraphyletic in Guzmania, Tillandsia, and Vriesea, the three largest genera. Flower, fruit, and seed morphology indicate at least three lineages in Guzmania, twelve in Tillandsia, and five in Vriesea. These lineages must berealigned in a new and more natural way. Recent transfers of species have demonstrated how unreliable the classifications of the latest monograph are and have altered the definitions of the involved genera. However, natural groups have only in part been recognized, their interrelations are still unclear, the use of DNA sequence data is mandatory to reconstruct phylogenies. The only available data based on ndhF gene sequences do not give good resolution of the phylogemetic tree and the authors have pointed out "That information from more highly variable sequences or the combining of data sets will be required for a clearer understanding of phylogenetic relationships". Correct phylogenetic relationships and generic definitions are indispensible for phytogeographic, evolutionary, ecological, and conservational evaluations as well as for reliable estimations of biodiversity. This study is the very first to combine different molecular markers and morphological data. Molecular studies are nowadays commonly accepted as a powerful tool in reconstructions of phylogenies of plant groups. The goal of the proposed studies is to generate data with the use of both chloroplast and nuclear DNA markers. In combination with a wide set of morphological characters redefinitions of present genera and he recognition of additional ones to establish monophyletic groups are focussed. This may serve as a model for subsequent analyses of the remaining two subfamilies and will be informative not only for the pineapple family but also for the dynamics of neotropical vegetation which is among the richest and most complex in the world.

Tillandsioideae is the largest of the three subfamilies comprising Alcantarea, Catopsis, Glomeropitcairnia, Guzmania, Mezobromelia, Racinaea, Tillandsia, Vriesea, and Werauhia, totalling about 1300 species. The existing morphological characterisation of these genera seems not to be very substantial for a natural grouping of the taxa, especially for species within the big genus Tillandsia (about 550 spp.). For our studies we have selected 110 samples (= 104 taxa) representing all nine currently accepted genera and their subgroups plus 10 taxa from the two remaining subfamilies and two samples of Stegolepis from the nearest related family Rapateaceae. In order to solve the existing problems in the circumscriptions of genera we have used two coding (rbcL and matK gene) and four non coding (atpB-rbcL intergenic spacer, trnL intron and trnL-trnF spacer, rps16 intron) plastid markers (total of more than 5000 base pairs). Up to now the present project is by far the most comprehensive molecular study in Bromeliaceae. Individual analyses of each marker show that matK has the best resolution, followed by rps16 intron, atpB-rbcL intergenic spacer and trnL intron and trnL-trnF spacer. On the whole rbcL gene shows poor resolution. For the final conclusions of this investigation we discuss the position of some strange species and the obvious paraphyletic and polyphyletic groups. The combined analysis resolves the major grouping at generic level and also indicates some geographic correlations: the basal branches of the cladogram coicide with geologically old areas while the taxa of the terminal branches are found in the geologically young Andes. The relatively higher phylogenetical age of the basal taxa is mirrored by the lengths of the branches in the phylogram. However, further study is necessary for a proper taxonomic grouping of Tillandsioideae, especially within polymorphic Tillandsia and with the use of nuclear markers. Comparison of the extensive morphological data with the combined molecular data will show the agreements and conflicts of both. Our project clearly demonstrates the power as well as the difficulties of the molecular methods in reconstructing phylogenies in plants. On the one hand they offer a more unbiassed approach but on the other hand our knowledge of variability and conclusiveness of the selected genomic fractions is still insufficient. Some arbitrariness can be excluded by combined analysis of different markers. However, due to low variability of numerous genetic markers statistical support of the results decreases and the probability of misinterpretations by the program increases or no resolution is achieved at all. Further study is needed to improve our understanding of the values of molecular markers and of the reliability of the pylogenies of our study groups.