Studies On Phylogeny And Molecular Evolution Of Batrachospermales (Rhodophyta)

Batrachospermum Roth is a genus belonging to Florideophceae,Rhodophyta, Batrachospermales, Batrachospermaceae. All species ofBatrachospermum live in freshwater. Batrachospermum is the type genus ofBatrachospermaceae, the species of which is abundant and adsperse. As therelict species retentional in freshwater since halarch succession, the speciesof Batrachospermum distribute in relatively exiguous regions, and thedistribution is affecting by special environmental factors, which result in theabundance of endemic species.The present paper describes the morphological features and life cycle ofBatrachospermum, and their regional distribution in China, including 2subgenera, 7 sections and 26 species (including varieties) that has beenreported in China.This paper reviews the foundation of Batrachospermum and the groupincluded, then summarizes the molecular markers commonly applied for thestudy of the phylogeny and evolution of Batrachospermum. The algae show18SrDNA, 26SrDNA and internal transcribed spacer (ITS) region in thenuclear genome, an rbcL sequence in chloroplast DNA, and a cox2-3 spacerin mitochondrial DNA. Also discussed is the new technique of inter simplesequence repeat (ISSR) and the expansion of the applicable range of eachmolecular marker. The ITS region is mainly used for populationdifferentiation and genetic analysis among closely related species, and ISSRis applicable for studying genetic diversity of interpopulations and individualvariation. As well, the cox2-3 spacer is sometimes used for investigatinggenetic diversity of individual variation, whereas the rbcL sequence and 18SrDNA could be used for molecular studies at interspecific and highertaxonomic levels. These markers have been shown in phylogeography,dispersal mechanisms and the origin of species.The four kinds of phylogenetic trees based on rbcL sequences are reconstructed, which contain 9 populations of 6 species in Batrachospermumcollected from China and 20 populations of 10 species abroad obtained fromGenBank. As combined with their morphological features, the phylogeneticrelationships within Batrachospermum Roth are analized.The results indicate that the speciments we get are located on the cladesof section Batrachospermum and section Contorta, according with theconclusion inferred from morphological analysis. The different populationsof each widespread species at home and abroad have high sequence identity.Molecular investigation data also testify the paraphyletic systematicrelationships in genus Batrachospermum.In all trees, the taxa of section Batrachospermum clearly do not form amonophyletic clade. The results show the close affinity of B. arcuatum and B.longipedicellatum, and the both are strongly positioned as the sister toanother two species of this section, B. involutum and B. boryanum. But thedifferent populations of B. anatinum do not form a monophyletic clade. B.gelatinosum appear to be distinct lineage from the clade including any othertaxa of section Batrachospermum, the similar association of two clades hasweak bootstrap support in the phylogenetic trees. These ideas are inaccordance with analysis of section Batrachospermum based on a variety ofwell-defined morphologic characteristics. It is assumed that sectionBatrachospermum is a paraphyletic group with long cladogenesis.In addition, section Virescentia and section Contorta are on an identicalbranch of molecular trees, which have weak boorstrap support in MP tree, NJtree and ML tree. Both above are at the base of the Batrachospermum clade.While based on Bayesian analysis section Virescentia and section Contortaappear to be distinct lineages, so the evolution positions of these two sectionsshould be further discussed.There are different genetic relationships between section Setacea andsection Turfosa in different phylogenetic trees, but the association of sectionTurfosa and section Batrachospermum is strongly supported by highbootstrap values. There are 366 parsimony-informative sites in the 1282bp region of rbcLsequence, rbcL gene has been proved to be a valid molecular marker formolecular studies of Batrachospermum. The history of phylogenesis ofBatrachospermum would have been acknowledged more truthfully whenmore molecular data were combined.