Abstract
Delimitating species boundaries could be of critical importance when evaluating the species' evolving process and providing guidelines for conservation genetics. Here, species delimitation was carried out on three endemic and endangered Cycas species with resembling morphology and overlapped distribution range along the Red River (Yuanjiang) in China: Cycas diananensis Z. T. Guan et G. D. Tao, Cycas parvula S. L. Yang and Cycas multiovula D. Y. Wang. A total of 137 individuals from 15 populations were genotyped by using three chloroplastic (psbA-trnH, atpI-atpH, and trnL-rps4) and two single copy nuclear (RPB1 and SmHP) DNA sequences. Basing on the carefully morphological comparison and cladistic haplotype aggregation (CHA) analysis, we propose all the populations as one species, with the rest two incorporated into C. diannanensis. Genetic diversity and structure analysis of the conflated C. diannanensis revealed this species possessed a relative lower genetic diversity than estimates of other Cycas species. The higher genetic diversity among populations and relative lower genetic diversity within populations, as well as obvious genetic differentiation among populations inferred from chloroplastic DNA (cpDNA) suggested a recent genetic loss within this protected species. Additionally, a clear genetic structure of C. diannanensis corresponding with geography was detected based on cpDNA, dividing its population ranges into “Yuanjiang-Nanhun” basin and “Ejia-Jiepai” basin groups. Demographical history analyses based on combined cpDNA and one nuclear DNA (nDNA) SmHP both showed the population size of C. diannanensis began to decrease in Quaternary glaciation with no subsequent expansion, while another nDNA RPB1 revealed a more recent sudden expansion after long-term population size contraction, suggesting its probable bottleneck events in history. Our findings offer grounded views for clarifying species boundaries of C. diannanensis when determining the conservation objectives. For operational guidelines, the downstream populations which occupy high and peculiar haplotypes should be given prior in-situ conservation. In addition, ex-situ conservation and reintroduction measures for decades of generations are supplemented for improving the population size and genetic diversity of the endemic and endangered species.
Highlights
The conceptualization and boundary of species are critically important and of great significance for taxonomists, ecologists and conservation biologists when identifying objective taxa and determining the protection units
Taxon Sampling A total of 137 individuals were selected for subsequent analysis from the 15 populations collected along the Red River region in China, including 10 populations of C. diannanensis, three populations of C. parvula and two populations of C. multiovula
DNA Sequences Characterization The combined chloroplastic sequence data of atpI-atpH, psbAtrnH, and trnL-rps4 was aligned as a consensus length of 1992 bp, containing 61 polymorphic sites among which 14 were substitutions and others were indels
Summary
The conceptualization and boundary of species are critically important and of great significance for taxonomists, ecologists and conservation biologists when identifying objective taxa and determining the protection units. As an endangered but quite recent (mid-Miocene) radiant gymnosperm genus (Nagalingum et al, 2011), phenotype variations can not necessarily assort Cycas into discrete categories. Some morphology-resembled or character-equivocal species due to interspecific hybridization were often put forward by a blended name of “complex” or “group” (see Hill, 1994a,b; Yang and Meerow, 1996; Liu, 2004; Xiao and Gong, 2006), making the definition of a species impeded to botanical studies of speciation
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