Abstract
The Mediterranean region is a center of species and genetic diversity of many plant groups, which served as a source of recolonization of temperate regions of Eurasia in Holocene. We investigate the evolutionary history of species currently classified in Lotus sect. Bonjeanea in the context of the evolution of the genus Lotus as a whole, using phylogenetic, phylogeographic and dating analyses. Of three species of the section, L. rectus and L. hirsutus have wide Mediterranean distribution while L. strictus has a disjunctive range in Bulgaria, Turkey, Armenia, Eastern Kazakhstan, and adjacent parts of Russia and China. We used entire nuclear ribosomal ITS1-5.8S-ITS2 region (nrITS) and a plastid dataset (rps16 and trnL-F) to reconstruct phylogenetic relationships within Lotus with an extended representation of Bonjeanea group. We analyzed the phylogeographic patterns within each species based on the plastid dataset. For divergence time estimation, the nrITS dataset was analyzed. Our results confirmed the non-monophyletic nature of the section Bonjeanea. They indicate that Lotus is likely to have diverged about 15.87 (9.99–19.81) million years ago (Ma), which is much older than an earlier estimate of ca. 5.54 Ma. Estimated divergence ages within L. strictus, L. rectus, and L. hisrutus (6.1, 4.94, and 4.16 Ma, respectively) well predate the onset of the current type of Mediterranean climate. Our data suggest that relatively ancient geological events and/or climatic changes apparently played roles in early diversification of Lotus and its major clades, as well as in formation of phylogeographic patterns, in at least some species.
Highlights
The genus Lotus clade is well supported by Bayesian and maximum likelihood (ML)
The analyses revealed a medium level of rate heterogeneity with the mean of the coefficient of rate variation 0.53 (95% highest posterior density HPD interval 0.3744–0.6978)
The mean age of the LoteaeSesbania clade is estimated from nuclear ribosomal ITS1-5.8S-ITS2 region (nrITS) sequences at 43.64 million years ago (Ma) (95% HPD: 32.47–49.09 Ma), whereas the Loteae crown age is 29.11 (18.28–34.82) Ma (Figure 8, Table 2)
Summary
Dorycnium Mill.) is the largest genus of the tribe Loteae (LeguminosaePapilionoideae) containing ca. 130 species of annual and perennial herbs, semishrubs, and shrubs or dwarf shrubs widely distributed in Eurasia, Africa, Australia and several islands of the Atlantic, Indian, and Pacific oceans [1]. Divided Lotus into 14 sections, and this classification was used as a base for molecular phylogenetic studies [4,5,6,7]. In the phylogeny of the genus Lotus, whose major center of species diversity is located in the Mediterranean region, an early split into “southern” and “northern” evolutionary lineages was discovered [6]. The northern lineage is supported by plastid data only and includes members of four sections: sect.
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