Evolution and biogeography of Balsaminaceae: insights from molecular phylogeny
Balsaminaceae has two genera: Hydrocera with only one species and Impatiens, with over 1000 species. Hydrocera is found in the Indo-Malaysia areas, and Impatiens is highly clustered in tropical Africa, Madagascar, southern India, the eastern Himalayas, Southeast Asia. Only a few Impatiens species are found in the temperate areas of the northern hemisphere. In order to have a better understanding of the morphological and karyological evolution, an seedcoat micromorphology investigation with 38 species of Impatiens and a karyological investigation with 45 species of Impatiens was carried out. A high diversity were found in seedcoat micromorphology of Impatiens. Four morphological types were distinguished. Taxonomic and phylogenetic implications of the seedcoat micromorphology are also discussed. Karyological investigations revealed the somatic chromosome numbers vary greatly from 2n=6 to 2n=66 in Impatiens. Considering all the available chromosomal data, x=7, 8, 9, 10 are the most frequent basic numbers of the family. Geographic distributions of the most frequent basic numbers show interesting patters in hotspots of Impatiens. The DNA molecular phylogenetics of this family were then explored. One nuclear DNA region, internal transcribed spacers (ITS) and two non-coding chloroplast DNA regions, trnL-trnF and aptB-rbcL have been chosen as DNA mark. 182 species of this family coming from different distribution center and three species of Marcgraviaceae and two species of Tetrameristaceae were amplified by PCR, sequenced and phylogenetically analyzed applying distance estimates and Bayesian method. Five phylogenetic topologies were received. They are congruent with each other, but not identical. Only combined Bayesian tree is well supported in most of the lineages. Molecular phylogeny results confirmed the monophyly of Balsaminaceae and Impatiens and it showed that the phylogenetic relationships in Impatiens are associated with geographic distribution, less defined by gross morphology. The parsimonious optimization of the centers of endemism onto the molecular phylogenies revealed that extant Impatiens species are of mainland Southeast Asian origin, from where dispersal to boreal Eurasia and North America, to central Asia and Eastern Europe via the Himalayas, and to India and Africa have occurred. The Madagascan Impatiens show an African origin. The character-state optimization suggested that spurred flower, narrowly-fusiform capsule, 4 lateral sepals, 3-colpate pollen and reticulate seedcoat represent the plesiomorphic states within Impatiens. Both x=8 and 10 might be the ancestral basic chromosome number in Balsaminaceae. The diverse and complicate specialization of floral structures of Balsaminaceae is pollinator-mediated, and therefore highly homoplasious.
Thèse de doctorat : Université de Neuchâtel, 2006 ; 1894
Type de publication
Resource Types::text::thesis::doctoral thesis
Dossier(s) à télécharger