Genetic Divergence between Two Sympatric Ecotypes of Phalaenopsis pulcherrima on Hainan Island

Xiangyu Hu,Xiqiang Song,Fusun Yang,Siren Lan,Zhe Zhang,Donghui Peng,Mingxun Ren

doi:10.3390/d13090446

Xiangyu Hu, Xiqiang Song + Show 5 more

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https://doi.org/10.3390/d13090446

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Abstract

Ecotypes are the result of ecological differentiation at the early stages of speciation. Adaptation to soil conditions offers arguably the best examples of local adaptation in plants. Two sympatric ecotypes, with either a red or green abaxial leaf surface, were found without clear geographical isolation in Phalaenopsis pulcherrima, a Southeast Asia endemic and endangered orchid. The soil of the red leaf ecotype has a higher water content and nutrient content than the green ecotype. What is the genetic structure of the two ecotypes? Is there complete or partial reproductive isolation between the two ecotypes? In this work, leaf reflection of the two ecotypes in P. pulcherrima were compared, to illustrate their difference in leaf color. The genetic differentiation between two ecotypes was examined, using ISSR and SRAP markers to determine the genetic structure of the populations. Our results showed that the green ecotype had reflectance spectrum peaks at 530 nm and 620 nm, while in the red ecotype, the peak at 530 nm was absent. A total of 165 ISSR and SRAP loci showed a high level of genetic diversity within the green ecotype, and analyses of the population structure revealed two genetic clusters that corresponded to the red and green ecotypes. The percentage of variation between the two ecotypes (24.55%) was greater than the percentage of variation among the populations (16.54%)—indicating partial reproductive isolation, high genetic differentiation, and that ecological differentiation has been more important than geographical barriers among populations within ecotypes. Most pairwise FST values between the populations within either ecotype on Hainan Island were less than 0.15; however, the FST between both the Thai and Malaysian populations and the Hainan Island population was greater than 0.25, due to South China sea isolation. Ecotypic differentiation is an important part of speciation; therefore, we must take into account the axes along which lineages sort, when formulating protection strategies.

Highlights

Ecotypes refer to groups of individuals within a species, with distinct phenotypic and genetic variations [1,2]
As an adaptation to soil conditions, serpentine populations completed flowering by midsummer, versus nonserpentine populations in late summer, which resulted in the reproductive isolation [27]
All of our clustering analyses show that the individuals of P. pulcherrima can be divided into two genetic clusters that correspond to the red and the green ecotype, with the exception of nine green individuals that cluster with the red ecotype

Summary

Introduction

Ecotypes refer to groups of individuals within a species, with distinct phenotypic and genetic variations [1,2]. It is widely recognized that ecotypes are the result of ecological differentiation at the early stages of speciation [5,6] This early stage is often characterized by the formation of partial reproductive isolation [7,8,9,10,11]. The inland ecotype has an earlier-flowering, annual life history to escape summer drought conditions, while the coastal ecotype—which receives coastal summer fog and cool temperatures—has maintained a perennial life history that is adapted to year-round soil water availability [16,17,18,19,20,21,22,23,24]. As an adaptation to soil conditions, serpentine populations completed flowering by midsummer, versus nonserpentine populations in late summer, which resulted in the reproductive isolation [27]

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