Phylogeny, species delimitation, and interspecific hybridization in Sphagnum section Acutifolia

Nucleotide sequences for six nuclear and one chloroplast loci were used to reconstruct phylogenetic relationships in the section Acutifolia.

The combined data matrix, which includes 136 accessions (129 ingroup taxa and 7 outgroups) and 5126 nucleotide sites, was analyzed using Bayesian inference. Most of the individual morphospecies generally recognized in the section were represented by multiple populations, in some cases by up to 16 accessions from throughout the Northern Hemisphere.

Results of the combined seven-locus analysis resolved many of the species as monophyletic, but the deeper nodes were generally without support. Separate analyses of single-locus data sets revealed significant conflicts, indicating interspecific gene flow within the section. Sequence data allowed likely parentage to be identified for several species of hybrid origin, and identified individual accessions that appear to be genetic admixtures.

Taxonomic conclusions that can be made from the analyses include: 1. Sphagnum wulfianum and S. aongstroemii should both be included in section Acutifolia, 2. S. subtile cannot be separated from S. capillifolium, and the two should be synonymized, 3. S. capillifolium and S. rubellum each contain a monophyletic core of populations and should be retained as separate species, but 4. S. rubellum cannot be separated from S. andersonianum and S. bartlettianum and they should be merged, 5. S. tenerum is highly differentiated from S. capillifolium and should be treated as a separate species, 6. inter-specific mixed ancestry is demonstrated for S. russowii (a likely allopolyploid), S. skyense, S. arcticum, and S. olafii.

Interspecific recombination appears to be rather common in the Acutifolia, yet species, for the most part, maintain cohesiveness.

Fig. 1. Phylogenetic reconstruction for Sphagnum sect. Acutifolia, based on heterogeneous Bayesian analyses of seven genomic regions. Thick branches are supported at ³ 95% Bayesian joint posterior probability. The accession of S. subtile (no. 1281, identified by J. Shaw and L. E. Anderson) indicated by a solid black circle does not group with other accessions of the morphospecies.

Reference:

Shaw, A. J., C. J. Cox, & S. B. Boles. 2005. Phylogeny, species delimitation, and interspecific hybridization in Sphagnum section Acutifolia. Systematic Botany 30: 16-33. reprint

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