Deciphering the Taxonomic Delimitation of Ottelia acuminata (Hydrocharitaceae) Using Complete Plastomes as Super-Barcodes

Yunheng Ji,Yonghong Zhang,Jin Yang,Zhenyan Yang,Jacob B. Landis,Shuying Wang

doi:10.3389/fpls.2021.681270

Abstract

Accurate species delimitation and identification, which is a challenging task in traditional morphology-based taxonomy, is crucial to species conservation. Ottelia acuminata (Hydrocharitaceae) is a severely threatened submerged macrophyte endemic to southwestern China. The taxonomy of O. acuminata, which has long been in dispute, remains unresolved, impeding effective conservation and management practices. Here, we aim to address the long-standing issues concerning species boundary and intraspecific subdivision of O. acuminata using complete plastome sequences as super-barcodes. The taxonomic delimitation of O. acuminata was explored using phylogenetic inference and two independent sequence-based species delimitation schemes: automatic barcode gap discovery (ABGD) and multi-rate Poisson tree processes (mPTP). The reciprocally reinforcing results support the reduction of the closely related congeneric species, O. balansae and O. guanyangensis, as two conspecific varieties of O. acuminata. Within the newly defined O. acuminata, accurate varietal identification can be achieved using plastome super-barcodes. These findings will help inform future decisions regarding conservation, management and restoration of O. acuminata. This case study suggests that the use of plastome super-barcodes can provide a solution for species delimitation and identification in taxonomically difficult plant taxa, thus providing great potential to lessen the challenges of inventorying biodiversity, as well as biologically monitoring and assessing threatened species.

Highlights

Species are a fundamental unit of biodiversity (Claridge et al, 1997)
The multi-rate Poisson tree processes (mPTP) analyses yielded the same delimitation scheme as automatic barcode gap discovery (ABGD) did: all individuals were grouped into two species-like units that coincide with the two putative species proposed by ABGD analyses (Figure 3), with both of them receiving high posterior support (PP = 1.00)
Two independent delimitation methods were used to explore species delimitation, which allows the methods to compensate for weaknesses of the other method to develop a robust taxonomic delimitation framework (e.g., Hebert et al, 2003; Kekkonen and Hebert, 2014; Mutanen et al, 2015)

Summary

Introduction

Species are a fundamental unit of biodiversity (Claridge et al, 1997). Estimating how many species are under threat is an essential step in setting conservation priorities (May, 1988; May and Beverton, 1990; Margules and Pressey, 2000; Dirzo and Raven, 2003; Mace et al, 2003). Recent general acceptance suggests that species should be recognized as evolutionarily distinct entities possessing significant morphological and evolutionary distinctiveness, or niche differentiation (de Queiroz, 1998; Wiley and Mayden, 2000; Sites and Marshall, 2003). This acceptance drove the development of a multidisciplinary approach that utilizes morphological, genetic, ecological, and even metabolomic data in discriminating species (Sites and Marshall, 2003; Duminil and Di Michele, 2009; Su et al, 2015; Eisenring et al, 2016; Cheng et al, 2020)

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Conclusion