Universität zu Köln

Reder, Tanja (2019). A case study of species delimitation with molecular methods: the algal genus Microthamnion (Microthamniales,Trebouxiophyceae). PhD thesis, Universität zu Köln.

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Abstract

The green algal genus Microthamnion (Microthamniales, Trebouxiophyceae) has been extensively studied, but the question of species delimitation remained a matter of controversy. The morphological traits used to discriminate species in Microthamnion have shown to be quite polymorphic, and the restriction enzyme analysis performed in a first molecular attempt does no longer meet modern standards. The present study used a detailed molecular approach and combined several methods to clarify the matter of species delimitation on a molecular level. A multi-gene alignment comprising the nuclear-encoded 18S, and 28S rRNA genes, and the ITS2 molecule, as well as the plastid-encoded rbcL gene was assembled and used for concatenated phylogenetic analyses. The 74 Microthamnion strains investigated in this study fell into four monophyletic clades (one with a distinct subdivision) and nine longbranched lineages, which are assumed to correspond to species level. An apomorphy analysis was performed in order to find non-homoplasious synapomorphies (NHSs), and thus unique molecular signatures, for the clades and lineages inferred from the phylogeny. In a novel approach that interpreted molecular data in an alternative way, these NHSs and other ‘phenotypic molecular characters’ were compiled in a data matrix and used for a parsimony tree reconstruction. The clade boundaries and lineages inferred from the Microthamnion phylogeny were confirmed by both, unique molecular signatures and the tree based on all phenotypic molecular characters, resulting in 14 putative species delineated by molecular methods.