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Open Access Research article

Indehiscent sporangia enable the accumulation of local fern diversity at the Qinghai-Tibetan Plateau

Li Wang123, Harald Schneider12, Zhiqiang Wu13, Lijuan He13, Xianchun Zhang1 and Qiaoping Xiang1*

Author Affiliations

1 State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, The Chinese Academy of Sciences, Beijing, 100093, China

2 Department of Botany, Natural History Museum, London, United Kingdom

3 Graduate University of Chinese Academy of Sciences, Beijing, China

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BMC Evolutionary Biology 2012, 12:158  doi:10.1186/1471-2148-12-158

Published: 28 August 2012

Abstract

Background

Indehiscent sporangia are reported for only a few of derived leptosporangiate ferns. Their evolution has been likely caused by conditions in which promotion of self-fertilization is an evolutionary advantageous strategy such as the colonization of isolated regions and responds to stressful habitat conditions. The Lepisorus clathratus complex provides the opportunity to test this hypothesis because these derived ferns include specimens with regular dehiscent and irregular indehiscent sporangia. The latter occurs preferably in well-defined regions in the Himalaya. Previous studies have shown evidence for multiple origins of indehiscent sporangia and the persistence of populations with indehiscent sporangia at extreme altitudinal ranges of the Qinghai-Tibetan Plateau (QTP).

Results

Independent phylogenetic relationships reconstructed using DNA sequences of the uniparentally inherited chloroplast genome and two low-copy nuclear genes confirmed the hypothesis of multiple origins of indehiscent sporangia and the restriction of particular haplotypes to indehiscent sporangia populations in the Lhasa and Nyingchi regions of the QTP. In contrast, the Hengduan Mountains were characterized by high haplotype diversity and the occurrence of accessions with and without indehiscent sporangia. Evidence was found for polyploidy and reticulate evolution in this complex. The putative case of chloroplast capture in the Nyingchi populations provided further evidence for the promotion of isolated but persistent populations by indehiscent sporangia.

Conclusions

The presented results confirmed the hypothesis that indehiscent sporangia promote the establishment of persistent population in different regions of the QTP. These results are consistent with the expectations of reproductive reassurance by promotion of self-fertilization that played a critical role in the assembly of populations in isolated locations and/or extreme habitats.

Keywords:
Chloroplast capture; Chloroplast DNA; Himalaya; Incongruent phylogenetic hypotheses; Lepisorus clathratus; Phylogenetic analyses; Reticulate evolution; Self-fertilization; Low-copy nuclear genes; PgiC; LFY