A high frequency of allopolyploid speciation in the gymnospermous genus Ephedra and its possible association with some biological and ecological features

Abstract

The origin and evolution of polyploids have been studied extensively in angiosperms and ferns but very rarely in gymnosperms. With the exception of three species of conifers, all natural polyploid species of gymnosperms belong to Ephedra, in which more than half of the species show polyploid cytotypes. Here, we investigated the origin and evolution of polyploids of Ephedra distributed in the Qinghai-Tibetan Plateau (QTP) and neighbouring areas. Flow cytometry (FCM) was used to measure the ploidy levels of the sampled species that are represented by multiple individuals from different populations, and then, two single-copy nuclear genes (LFY and DDB2) and two chloroplast DNA fragments were used to unravel the possible origins and maternal donors of the polyploids. The results indicate that the studied polyploid species are allopolyploids, and suggest that allotetraploidy is a dominant mode of speciation in Ephedra. The high percentage of polyploids in the genus could be related to some of its biological attributes such as vegetative propagation, a relatively high rate of unreduced gamete formation, and a small genome size relative to most other gymnosperms. Significant ecological divergences between allotetraploids and their putative progenitors were detected by PCAs and anova and Tukey's tests, with the exception of E. saxatilis. The overlap of geographical distributions and ecological niches of some diploid species could have provided opportunities for interspecific hybridization and allopolyploid speciation.

Geographical or ecological divergence between the parapatric species Ephedra sinica and E. intermedia?

“…Previous reports suggested that the two Old World tetraploid Ephedra species, E. intermedia and E. sinica, were positioned in a monophyletic clade (Huang et al 2005;Qin et al 2013;Wu et al 2016), partially due to the lack of significant phenotypes and weak phylogenetic signals. In this work, based on the sequence variations of four cpDNA fragments, we detected 14 haplotypes, which suggested that these two species formed a monophyletic clade and that E. intermedia is paraphyletic due to the populations WQ and BYBL (Fig.…”

Divergence in Eco-Physiological Responses to Drought Mirrors the Distinct Distribution of Chamerion angustifolium Cytotypes in the Himalaya–Hengduan Mountains Region

“…In the Himalaya–Hengduan Mountains region, limited biogeographic studies manifested that diploid and derivative polyploids colonizing different distribution areas (Liang et al, 2015; Wu et al, 2016), with some polyploids tending to occur at high altitudes, such as Aconitum (Yuan and Yang, 2006), Allium przewalskianum (Cui et al, 2008), and Anaphalis nepalensis (Meng et al, 2014). Although geographical segregation of cytotypes has long been recognized, the underlying mechanisms creating these patterns remain poorly understood (McIntyre, 2012).…”

A genome for gnetophytes and early evolution of seed plants

“…In gymnosperms, WGDs have been reported for conifers, G. biloba and cycads (a likely shared WGD) 14,29,30 . Although recent polyploidy seems common in extant Ephedra 31 , evidence for ancient WGDs in gnetophytes is missing (Supplementary Information and Supplementary Fig. 7), except for a WGD in Welwitchia which is likely to have occurred after the divergence of its lineage from that leading to Ephedra (Supplementary Fig.…”