Molecular phylogeny of the genus Hypochaeris using internal transcribed spacers of nuclear rDNA: inference for chromosomal evolution

Abstract

Sequences of the internal transcribed spacers (ITSs) of 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships and chromosomal evolution among 14 species of the genus Hypochaeris (Asteraceae). Parsimony analysis was performed for phylogenetic reconstruction, and sequence divergence between species was estimated. Pairwise sequence divergence within Hypochaeris genus ranged from 0% to 25.68% in ITS1 and from 0% to 17.08% in ITS2. A highly resolved strict-consensus tree was obtained that showed the phylogenetically useful information of ITS sequences within the genus Hypochaeris. Four clades could be well distinguished, one of them formed by the single species H. robertia, which appeared to be the most related to the ancestral species of the genus. The results agree with taxonomic classification based on morphological data, and the tree obtained, when indels are coded as missing data, aggregates the species having the same chromosome number, except in one clade. According to the ITS phylogenetic tree, the chromosomal evolution within the genus Hypochaeris conflicts with the previous hypothesis and suggests that karyotype evolution in Hypochaeris was accompanied with both decreasing and increasing dysploidy, probably with several chromosomal rearrangements, and from an ancestral basic chromosome number of 4 or 5.

Phylogenetic relationships in the North African genus Hedysarum as inferred from ITS sequences of nuclear ribosomal DNA

“…Thus, we assume that both ITS1 and ITS2 sequences are characterised by a considerable degree of genetic homology in this species. Similar results are obtained in other genera such as Hypochaeris (Asteraceae) (Cerbah et al 1998) and Calycadenia (Asteraceae) (Baldwin 1993). Hence it can be inferred that a consensus ITS sequence characterises each Hedysarum species and therefore analysis of any ITS derived from any individual of each species would be sufficient to investigate inter-specific polymorphism.…”

“…Therefore, a consensus ITS sequence that characterises each Hedysarum species could be strongly suggested since a lack of variation either in the length or in the sequences has been scored. Note that similar data describing the establishment of a consensus ITS sequence have been reported in other species (Baldwin 1993;Cerbah et al 1998 In addition, phylogeny within the genus Hedysarum based on the ITS sequence analysis provided sufficient and useful information for reconstructing a general structure of the species analysed. Thus, we assume that trees' topology derived from analysis of the ITS1 and ITS2 sequences taken together or separately are nearly similar except for the H. pallidum species characterised by different clustering within the other ones according to the analysed sequence due to the presence of specific variation in the surveyed regions.…”

Trends in site-number change of rDNA loci during polyploid evolution in Sanguisorba (Rosaceae)

“…Dysploid reduction is a common phenomenon in flowering plants and is well known in the Campanulaceae (Stace and James 1996), Compositae (Baldwin 1993;Cerbah et al 1998;Watanabe et al 1999), Gentianaceae (Yuan and Kupfer 1997), Iridaceae (Goldblatt and Takei 1997), and Rutaceae (Stace et al 1993). In Rosaceae, dysploid reduction from n=17 to n=15 is known in Vauquelinia (Morgan et al 1994), although this is the only known example in the family.…”

Ribosomal DNA Evidence and Disjunctions of Western American Portulacaceae

“…The importance of LDD in the historical development of island and particular continental floras has been widely recognized (Raven, 1972;Raven and Axelrod, 1974), but the relative contribution of LDD to continental floras in general has been difficult to determine. In some cases, phylogenetic analysis has provided additional evidence for relatively recent divergence among taxa occupying disjunct habitats that were directly connected in the more remote past (e.g., Luckow and Hopkins, 1995;Bruneau, 1996;Fritsch, 1996;Hershkovitz and Zimmer, 1997;Erikkson and Donoghue, 1997;Morton et al, 1997;Olmstead and Palmer, 1997;Swenson and Bremer, 1997;Baum et al, 1998;Cerbah et al, 1998;Fay et al, 1998;Jobst et al, 1998;Roeland et al, 1998;Wagstaff and Garnock-Jones, 1998). In a more sublime example, phylogenetic analysis has demonstrated how LDD followed by hybridization with indigenous species may factor into the origin and evolution of genomes, even if the colonizing species is no longer present or extant (Wendel et al, 1995).…”