Molecular Phylogeny and Divergence Time Estimation of Onobrychis sect. Onobrychis (Fabaceae) based on nrDNA ITS

Abstract

Phylogenetic analysis and estimating divergence time of O. sect. Onobrychis were conducted using nrDNA ITS sequence data. A total of 60 species from the section Onobrychis, seven species of the five sister sections belonging to O. subgen. Sisyrosema and eight species of other genera of the tribe Hedysareae (Eversmannia subspinosa ، Greuteria argyreum، Corethrodendron multijugum ، Taverniera cuneifolia، Hedysarum polybotrys، Sulla spinosissima و Alhagi maurorum) as outgroups were chosen. Phylogenetic analyses were performed by maximum likelihood and Bayesian methods. The results showed that O. sect. Onobrychis is monophyletic and composed of two main well-supported clades. The first clade includes annual and perennial species with long wings, often with the basic chromosome number x= 8. The second clade comprises perennial species with short wings and two annuals with long wings, having the basic chromosome number x= 7. Sect. The divergence time estimation of this section was analyzed with BEAST. The section was originated at 11.96 Mya in middle Miocene and subsequently diverged into two linages at 9.29-9.58 Mya.IntroductionThe genus Onobrychis Mill. comprises ca. 170 annual or perennial herbs divided into two subgenera and nine sections. At the current status, O. sect. Onobrychis with merging sects. Lophobrychis and Dendrobrychis is the largest section of the genus. Materials and MethodsIn this study, phylogenetic analysis and estimating divergence time of O. sect. Onobrychis were conducted using nrDNA ITS. A total of 60 species from the section Onobrychis, seven species of the five sister sections belonging to O. subgen. Sisyrosema and eight species of other genera of the tribe Hedysareae (Eversmannia subspinosa, Greuteria argyreum, Corethrodendron multijugum, Taverniera cuneifolia, Hedysarum polybotrys, Sulla spinosissima, and Alhagi maurorum) as out-groups were chosen. Phylogenetic analyses were performed by maximum likelihood and Bayesian methods. The divergence times estimation of this section was analyzed with BEAST. FindingsThe results showed that O. sect. Onobrychis is monophyletic and composed of two main well-supported clades including clade “A” and clade “B”. Each clad was divided into several subclades. Results and ConclusionsThe first clade includes annual and perennial species with long wings, often with the basic chromosome number x= 8, and the second one composes species with the basic chromosome number x= 7. It was also found that the annual species that were previously classified in the sect. Lophobrychis were not monophyletic, and three long-winged annual species were placed in clade “A”, and two annual long-winged species were related to short-winged perennial species, are placed in clade “B”. But the two long-winged species O. cornuta and O. elymaitica, were previously classified in the sect. Dendrobrychis, are placed in the clade “A”. Sect. Onobrychis originated at 11.96 Mya in the middle Miocene and was subsequently diverged into two lineages at 9.29-9.58 Mya.

Keywords

• divergence time
• fabaceae
• nrdna its
• onobrychis
• phylogeny