Polymorphism of ITS sequences in 35S rRNA genes in Elymus dahuricus aggregate species: two cryptic species?

A V Rodionov,K S Dobryakova,N N Nosov,A A Gnutikov,E O Punina,A A Kriukov,V S Shneyer

doi:10.18699/vj19.493

Abstract

Nuclear ribosomal internal transcribed spacer (ITS) sequences were sequenced for 23 species and subspecies of Elymus sensu lato collected in Russia. The Neighbor-Net analysis of ITS sequences suggested that there are four ribotypes called Core Northern St-rDNA, Core Southern St-rDNA, Northern dahuricus St-rDNA and Southern dahuricus St-rDNA. The Core Southern variant of St-rDNA is closely related to rDNA of diploid Pseudoroegneria stipifolia (PI 313960) and P. spicata (PI 547161). The Core Northern St-rDNA is closely related to rDNA of P. cognata (PI 531720), a diploid species of Kyrgyzstan carrying StY variant of the St genome. The Core Northern St-rDNA is widespread among the Elymus species of Siberia and the Far East, including Yakutia and Chukotka. The Core Southern St-ribotype is typical of southern Elymus and Pseudoroegneria of the South Caucasus, Primorye, Pakistan, and South Korea. The Northern dahuricus St-ribotype and Southern dahuricus St-ribotype are derivatives of the Core Northern and Core Southern St-ribotypes, correspondingly. Both of them were found in all four studied species of the E. dahuricus aggregate: E. dahuricus Turcz. ex Griseb., E. franchetii Kitag., E. excelsus Turcz. ex Griseb. and Himalayan E. tangutorum (Nevski) Hand.-Mazz. In other words, there are at least two population groups (two races) of the Elymus dahuricus aggregate species that consistently differ in their ITS-sequences in Siberia, the Far East and Northern China. Each contains all morphological forms, which taxonomists now attribute either to different species of E. dahuricus aggr. (E. dahuricus sensu stricto, E. franchetii, E. tangutorum, E. excelsus) or subspecies of Campeiostachys dahurica (Turcz. ex Griseb.) B.R. Baum, J.L. Yang et C.C. Yen. At the moment it is unknown if there are any morphological differences between plants carrying either Northern or Southern dahuricus rDNA. Probably, they are cryptic species, but it is certain that if differences in morphology between the two races exist, they are not associated with signs that are now considered taxonomically significant and are used to separate E. dahuricus s. s., E. franchetii, E. tangutorum, and E. excelsus.

Highlights

The beginning of the 21 century was marked by very wide using of DNA sequencing in systematics and phylogeny of animals and plants
We suggest that cryptic species may exist in particular, in the genus Elymus L. (Triticeae)
In the present study we have shown that all species of Elymus in eastern Eurasia can be divided, according to their internal transcribed spacer (ITS) sequences, into two families of ribotypes, conventionally called by us as the “Northern” and the “Southern” variants of St-rDNA

Summary

Introduction

The beginning of the 21 century was marked by very wide using of DNA sequencing in systematics and phylogeny of animals and plants. Remarkable result of this was an exponential rise in the discovery of cryptic species in different groups of animals (Bickford et al, 2007). It is considered the genus Elymus is represented in Russia by 53 species (Tzvelev, Probatova, 2010). Based on the results of interspecies hybridization, DNA sequencing and GISH, it has been suggested that all the Elymus species share a common St subgenome originated from the genus Pseudoroegneria (Nevski) Á. Dewey could not be excluded (Okito et al, 2009), for the Asiatic Elymus species with StY and StHY genome compositions

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