Nuclear and Nucleomorph SSU rDNA Phylogeny in the Cryptophyta and the Evolution of Cryptophyte Diversity |
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Authors: | Kerstin Hoef-Emden Birger Marin Michael Melkonian |
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Institution: | 1.Universit?t zu K?ln, Botanisches Institut, Lehrstuhl I, Gyrhofstr. 15, 50931 K?ln, Germany,DE |
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Abstract: | The plastid-bearing members of the Cryptophyta contain two functional eukaryotic genomes of different phylogenetic origin,
residing in the nucleus and in the nucleomorph, respectively. These widespread and diverse protists thus offer a unique opportunity
to study the coevolution of two different eukaryotic genomes within one group of organisms. In this study, the SSU rRNA genes
of both genomes were PCR-amplified with specific primers and phylogenetic analyses were performed on different data sets using
different evolutionary models. The results show that the composition of the principal clades obtained from the phylogenetic
analyses of both genes was largely congruent, but striking differences in evolutionary rates were observed. These affected
the topologies of the nuclear and nucleomorph phylogenies differently, resulting in long-branch attraction artifacts when
simple evolutionary models were applied. Deletion of long-branch taxa stabilized the internal branching order in both phylogenies
and resulted in a completely resolved topology in the nucleomorph phylogeny. A comparison of the tree topologies derived from
SSU rDNA sequences with characters previously used in cryptophyte systematics revealed that the biliprotein type was congruent,
but the type of inner periplast component incongruent, with the molecular trees. The latter is indicative of a hidden cellular
dimorphism (cells with two periplast types present in a single clonal strain) of presumably widespread occurrence throughout
cryptophyte diversity, which, in consequence, has far-reaching implications for cryptophyte systematics as it is practiced
today. |
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Keywords: | : Cryptophyta — Cryptomonads — Nucleomorph — Coevolution — SSU rRNA — Phylogeny — Dimorphism — Cryptomonas — Biliproteins — Periplast — Campylomonas |
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