Phylogenetic analyses and chromosome counts reveal multiple cryptic species in Bupleurum commelynoideum (Apiaceae)

Abstract

Bupleurum commelynoideum H. Boissieu is a perennial herb occurring throughout the Hengduan Mountains region. This species was found to have more than one chromosome number in our previous chromosomal study. For a better understanding of its intraspecific genetic differentiation and interspecific relationships with other Bupleurum members, phylogenetic relationships among 15 populations of B. commelynoideum and 22 other Bupleurum members were investigated using the nuclear ribosomal DNA internal transcribed spacer (ITS) region and three chloroplast DNA (cpDNA) fragments (trnL‐F, rps16, and rpl32‐trnL). Both phylogenetic analyses of the ITS region and combined cpDNA data indicated that B. commelynoideum has more than one geographically delimited lineage. Among them, accessions from Shangri‐La and other regions were considered as different cryptic species according to the unified species concept. Our analyses also revealed that a complex pattern of reticulate relationship exists in B. commelynoideum and its allied species. The chromosome numbers of four populations of B. commelynoideum and a closely related species B. rockii H. Wolff are reported. The results showed that the chromosome number of B. commelynoideum has abundant variations in both chromosome ploidy (2x; 4x; 6x) and basic chromosome number (x = 5; x = 6). Population DXS (x = 6), which has the different basic chromosome number, should represent a different kind of cryptic speciation in B. commelynoideum. The karyological evidence, together with the molecular data, indicated that the existence of at least three cryptic species in B. commelynoideum. This kind of genetic differentiation without morphological divergence might be caused by stabilizing selection imposed by the extreme environmental conditions of the alpine area.

RAD sequencing data reveal a radiation of willow species (SalixL., Salicaceae) in the Hengduan Mountains and adjacent areas

“…Allopolyploidy was considered as another mechanism of the species diversification/ radiations on the HDM (Wen et al 2014). Chen et al (2007) suggested that polyploidization played an important role in speciation in Buddleja in this area, which is supported by the findings of Ma et al (2014) in Bupleurum . Our results so far indicate that the frequency of polyploid species in the HDM clade is close to the average rate in vascular plants of HDM (22%; Nie et al 2005).…”

Plastid DNA variation of the endemic species Oxytropis glandulosa Turcz. (Fabaceae)

“…A group of competent authors proposed to describe autopolyploid cytotypes as separate species (Soltis et al, 2007). Cryptic species produced by polyploidy were revealed in some species or species complexes (Liu et al, 2013;Britton et al, 2014;Ma et al, 2015), including legume species such as Leucaena species (Govindaralulu et al, 2011) or Medicago prostrata Jacq. (Eriksson et al, 2017).…”

“…Cryptic species are defined as two or more distinct lineages that are classified as a single nominal species, owing to the fact that they are difficult or impossible to be distinguished based on morphological characters alone (Ma et al, 2015;Shneyer and Kotseruba, 2015). The existence of cryptic species in plants was associated primarily with polyploidy.…”

“…they are separately evolving lineages, sensu De Queiroz (2007). Some species studied (Ma et al, 2015;Eriksson et al, 2017) comprise multiple, evolutionarily independent lineages, which, despite their potentially cryptic nature, qualify as species under the unified species concept (De Queiroz, 2007). Presumably tetraploid O. glandulosa populations should be regarded as a different species from the diploids, despite no known morphological distinctiveness between them.…”

A tool for the analysis of chromosomes: KaryoType

“…To account for these problems, we have developed Karyo-Type, a program which was developed on plant chromosomes but can be applied to chromosomes of other organisms. The beta version of KaryoType (named NucType) has been tested for years, and was successfully applied in previous research (Gao & al., 2012;Zhao & al., 2014;Ma & al., 2015;Li & al., 2016). The primary function of the software is to allow efficient chromosome measurements and karyotype analysis, including chromosome number and size, arm ratio, centromeric index, relative lengths and karyotype formula.…”