Cytotype distribution and chloroplast phylogeography of the Actinidia chinensis complex

Zhi Wang,Chunlin Yan,Zuozhou Li,Xiaohong Yao,Dawei Li,Caihong Zhong

doi:10.1186/s12870-021-03099-y

Abstract

BackgroundPlant phylogeographic studies of species in subtropical China have mainly focused on rare and endangered species, whereas few studies have been conducted on taxa with relatively wide distribution, especially polyploid species. We investigated the cytotype and haplotype distribution pattern of the Actinidia chinensis complex, a widespread geographically woody liana with variable ploidy in subtropical China comprising two varieties, with three chloroplast fragments DNA (ndhF-rpl132, rps16-trnQ and trnE-trnT). Macroevolutionary, microevolutionary and niche modeling tools were also combined to disentangle the origin and the demographic history of the species or cytotypes.ResultsThe ploidy levels of 3338 individuals from 128 populations sampled throughout the species distribution range were estimated with flow cytometry. The widespread cytotypes were diploids followed by tetraploids and hexaploids, whereas triploids and octoploids occurred in a few populations. Thirty-one chloroplast haplotypes were detected. The genetic diversity and genetic structure were found to be high between varieties (or ploidy races) chinensis and deliciosa. Our results revealed that these two varieties inhabit significantly different climatic niche spaces. Ecological niche models (ENMs) indicate that all varieties’ ranges contracted during the Last Inter Glacial (LIG), and expanded eastward or northward during the Last Glacial Maximum (LGM).ConclusionsPliocene and Plio-Pleistocene climatic fluctuations and vicariance appear to have played key roles in shaping current population structure and historical demography in the A. chinensis complex. The polyploidization process also appears to have played an important role in the historical demography of the complex through improving their adaptability to environmental changes.

Highlights

Plant phylogeographic studies of species in subtropical China have mainly focused on rare and endangered species, whereas few studies have been conducted on taxa with relatively wide distribution, especially polyploid species
Sixteen triploids having similar morphological characteristics with var. chinensis were observed in the diploid, tetraploid, and mixed populations (2x, 4x), whereas rare octoploids were found in two hexaploid var. deliciosa populations and one mixed population (2x, 4x, and 6x), respectively
The subsequent phylogenetic analysis showed that two parts of the tetraploids belonged to two different lineages (Fig. 3a) which have differentiated at 2.22 million years ago (Ma)

Summary

Introduction

Plant phylogeographic studies of species in subtropical China have mainly focused on rare and endangered species, whereas few studies have been conducted on taxa with relatively wide distribution, especially polyploid species. As an area harboring many ancient endemic genera and families, the subtropical region in China has recently attracted much attention due to its complex topography and fluctuated paleoclimate [5,6,7] Most of these phylogeographic studies in these two hotspots of China have mainly focused on rare and endangered species [8,9,10,11], with few cases examined in the species with a relatively widespread range [12, 13], especially for polyploid species. The Actinidia chinensis complex is a geographically widespread woody liana with variable ploidy in subtropical China It is widely planted around the world as an important horticultural fruit tree crop. The genetic diversity and population divergence history of the A. chinensis complex and correlations based on ploidy level are still unclear

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