Extreme Multiple Reticulate Origins of the Pteris cadieri Complex (Pteridaceae)

Yi-Shan Chao,Wen-Liang Chiou,Ho-Yih Liu,Yu-Chung Chiang,Shi-Yong Dong

doi:10.3390/ijms13044523

Abstract

The Pteris cadieri complex displays extensive morphological variation and seems to have originated through hybridization. However, the members of this complex reproduce by apogamy, which usually limits genetic variation. To evaluate the hypotheses of hybrid origins, the pattern of evolution in this species complex is reconstructed. Multiple methodologies were used. Diploids, triploids, and tetraploids were identified by chromosome counts and flow cytometry. Nuclear DNA markers (cytosolic phosphoglucose isomerase gene, PgiC) were used, together with chloroplast DNA markers (atpB-rbcL spacer and rbcL gene) to infer the biparental and maternal lineages of the Pteris cadieri complex. The three cpDNA haplotype groups and five PgiC alleles found in this study indicate that the evolution of the Pteris cadieri complex has been extremely reticulate. Up to 11 taxa belonging to eight morphs were identified. By comparing genetic variation in the Pteris cadieri in two independent areas, Hainan and Taiwan, we inferred that hybridization has occurred independently in different areas. Furthermore, we found evidence for phenological divergence (evergreen and deciduous) within Taiwan. We propose that the Pteris cadieri complex originated from different genetic lineages through multiple hybridizations in different geographical areas, leading to its present morphological diversity.

Highlights

Plants arising from hybridization usually have varied morphologies, which usually exhibit a gradual cline [1,2]
Samples were collected of each morphological variant in the Pteris cadieri complex from six populations in Hainan and 21 populations in Taiwan
The Pteris cadieri complex is apogamous, which is usually thought to be with low genetic variation

Summary

Introduction

Plants arising from hybridization usually have varied morphologies, which usually exhibit a gradual cline [1,2]. The hybrids can cross with their parents and result in offspring with diverse genetic characters [3,4,5]. The delimitation of hybrid offsprings and the parental species becomes gradually indistinguishable. Most hybrid fern species seem to have high levels of genetic variation, apogamous ferns, usually the result of hybridization, have limited genetic variation [12]. Apogamy is a special form of asexual reproduction in ferns and provides a means for overcoming the inability of non-homologous chromosomes to pair in hybrid ferns [13,14,15]. The parents and offspring of apogamous ferns have almost identical genetic characters and express the same morphologies. The mechanism of apogamy creates reproductive barriers that prevent gene flow among closely-related taxa, facilitating sympatric speciation

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Results

Discussion

Conclusion