Phylogeny, biogeography, and molecular dating of cornelian cherries (Cornus, Cornaceae): tracking Tertiary plant migration.

Data from four DNA regions (rbcL, matK, 26S rDNA, and ITS) as well as extant and fossil morphology were used to reconstruct the phylogeny and biogeographic history of an intercontinentally disjunct plant group, the cornelian cherries of Cornus (dogwoods). The study tests previous hypotheses on the relative roles of two Tertiary land bridges, the North Atlantic land bridge (NALB) and the Bering land bridge (BLB), in plant migration across continents. Three approaches, the Bayesian, nonparametric rate smoothing (NPRS), and penalized likelihood (PL) methods, were employed to estimate the times of geographic isolations of species. Dispersal and vicariance analysis (DIVA) was performed to infer the sequence and directionality of biogeographic pathways. Results of phylogenetic analyses suggest that among the six living species, C. sessilis from western North America represents the oldest lineage, followed by C. volkensii from Africa. The four Eurasian species form a clade consisting of two sister pairs, C. mas-C. officinalis and C. chinensis-C. eydeana. Results of DIVA and data from fossils and molecular dating indicate that the cornelian cherry subgroup arose in Europe as early as the Paleocene. Fossils confirm that the group was present in North America by the late Paleocene, consistent with the DIVA predictions that, by the end of the Eocene, it had diversified into several species and expanded its distribution to North America via the NALB and to Africa via the last direct connection between Eurasia and Africa prior to the Miocene, or via long-distance dispersal. The cornelian cherries in eastern Asia appear to be derived from two independent dispersal events from Europe. These events are inferred to have occurred during the Oligocene and Miocene. This study supports the hypothesis that the NALB served as an important land bridge connecting the North American and European floras, as well as connecting American and African floras via Europe during the early Tertiary.

Xiang QY ，Manchester SR ，Thomas DT ，Zhang W ，Fan C ... -  《EVOLUTION》

Reticulate evolution in Thuja inferred from multiple gene sequences: implications for the study of biogeographical disjunction between eastern Asia and North America.

The eastern Asia-North America disjunction is one of the most interesting biogeographical patterns, but its formation is still in much debate. Here nucleotide sequences of five cpDNA regions, nrDNA ITS and two low-copy nuclear genes (LEAFY, 4CL) were employed to reconstruct the phylogeny and to explore the historical biogeography of Thuja, a typical eastern Asia-North America disjunct genus. High topological discordance was observed between chloroplast and nuclear gene trees, even between different nuclear gene trees, suggesting that Thuja could have a reticulate evolutionary history due to multiple interspecific hybridization events. The eastern Asian species Thuja koraiensis might have obtained its chloroplast genome from the eastern North American species T. occidentalis by chloroplast capture, while the western North American species T. plicata is very likely to have inherited a recombinant cpDNA. Based on the phylogenetic analysis of multiple genes, DIVA-reconstruction of the distribution history, molecular clock estimation and fossil data, we inferred that Thuja could have originated from the high-latitude areas of North America in the Paleocene or earlier with subsequent expansion into eastern Asia through the Bering Land Bridge. The two eastern Asia species T. standishii and T. sutchuenensis have a sister relationship, and their split could have occurred in the Oligocene or early Miocene. In the present study, the selection of molecular markers in biogeographic studies was also discussed. Since most previous studies on the eastern Asia and North America disjunction are based on uniparentally inherited cpDNA and (or) directly sequenced nrDNA ITS data, the historical reticulate evolution in the studied groups might have been underestimated. Therefore, we suggest that multiple genes from different genomes, especially low-copy nuclear genes, be used in this research area in the future.

Peng D ，Wang XQ 《MOLECULAR PHYLOGENETICS AND EVOLUTION》

Molecular evidence for an Asian origin and a unique westward migration of species in the genus Castanea via Europe to North America.

The genus Castanea (Fagaceae) is widely distributed in the deciduous forests of the Northern Hemisphere. The striking similarity between the floras of eastern Asia and those of eastern North America and the difference in chestnut blight resistance among species has been of interest to botanists for a century. To infer the biogeographical history of the genus, the phylogeny of Castanea was estimated using DNA sequence data from different regions of the chloroplast genome. Sequencing results support the genus Castanea as a monophyletic group with Castanea crenata as basal. The three Chinese species form a strongly supported sister clade to the North American and European clade. A unique westward expansion of extant Castanea species is hypothesized with Castanea originating in eastern Asia, an initial diversification within Asia during the Eocene followed by intercontinental dispersion and divergence between the Chinese and the European/North American species during the middle Eocene and a split between the European and the North American species in the late Eocene. The differentiation within North America and China might have occurred in early or late Miocene. The North America species are supported as a clade with C. pumila var. ozarkensis, the Ozark chinkapin, as the basal lineage, sister to the group comprising C. pumila var. pumila, the Allegheny chinkapin, and Castanea dentata, the American chestnut. Morphological evolution of one nut per bur in the genus may have occurred independently on two continents.

Lang P ，Dane F ，Kubisiak TL ，Huang H ... -  《MOLECULAR PHYLOGENETICS AND EVOLUTION》

Phylogenetic relationships, divergence time estimation, and global biogeographic patterns of calopterygoid damselflies (odonata, zygoptera) inferred from ribosomal DNA sequences.

Dumont HJ ，Vanfleteren JR ，De Jonckheere JF ，H Weekers PH ... -  《SYSTEMATIC BIOLOGY》

Phylogenetic placement and biogeography of the North American species of Valerianella (Valerianaceae: Dipsacales) based on chloroplast and nuclear DNA.

Although Valerianaceae is a relatively small group of angiosperms (ca. 350 species), sample sizes of previous phylogenetic studies have been limited and taxonomic sampling has been usually geographically biased to species from Europe and/or South America. One group that has never been included in any analyses to date is the North American representatives of Valerianella. In this study I sampled 17 additional accessions from Valerianaceae, including six of the 12 described North American Valerianella species and four additional samples of European Valerianella species. Phylogenies based on parsimony and Bayesian methods show strong support for placing the North American Valerianella nested within the European species. These analyses also found Fedia to be nested within Valerianella, making Valerianella paraphyletic, a result consistent with several previously published molecular phylogenies. Divergence times estimated from the molecular data using recently proposed Bayesian 'relaxed' clock methods, suggest Valerianella was in North America by the middle Miocene (ca. 16-14 million years ago). These dates would suggest the North American species of Valerianella arrived in the New World just prior to the North Atlantic land bridge (NALB) no longer being a viable conduit for migration. Given the large amount of uncertainty in the divergence time estimates, dispersal across the North Atlantic may not be the only viable alternative to explain the current distribution of Valerianella. However, biogeographic analyses using an explicit model based approach, strongly favor the NALB as the route of dispersal for Valerianella.

Bell CD 《MOLECULAR PHYLOGENETICS AND EVOLUTION》