Great Genetic Differentiation among Populations of Meconopsis integrifolia and Its Implication for Plant Speciation in the Qinghai-Tibetan Plateau

The complex tectonic events and climatic oscillations in the Qinghai-Tibetan Plateau (QTP), the largest and highest plateau in the world, are thought to have had great effects on the evolutionary history of the native plants. Of great interest is to investigate plant population genetic divergence in the QTP and its correlation with the geologic and climatic changes. We conducted a range-wide phylogeographical analysis of M. integrifolia based on the chloroplast DNA (cpDNA) trnL-trnF and trnfM-trnS regions, and defined 26 haplotypes that were phylogenetically divided into six clades dated to the late Tertiary. The six clades correspond, respectively, to highly differentiated population groups that do not overlap in geographic distribution, implying that the mountain ranges acting as corridors or barriers greatly affected the evolutionary history of the QTP plants. The older clade of M. integrifolia only occurs in the southwest of the species' range, whereas the distributions of younger clades extend northeastward in the eastern QTP, suggesting that climatic divergence resulting from the uplift of the QTP triggered the initial divergence of M. integrifolia native to the plateau. Also, the nrDNA ITS region was used to clarify the unexpected phylogenetic relationships of cpDNA haplotypes between M. integrifolia and M. betonicifolia. The topological incongruence between the two phylogenies suggests an ancestral hybridization between the two species. Our study indicates that geographic isolation and hybridization are two important mechanisms responsible for the population differentiation and speciation of Meconopsis, a species-rich genus with complex polyploids

Multiplying Diversity: Family Unification and the Regional Origins of Late-Age US Immigrants

Building on claims that the family unification provisions of 1965 Amendments drive changes in both the age composition and the regional origins of US legal permanent residents, we use administrative data to examine empirically whether and how chain migration links these two trends. Specifically, we ask: (1) How does the prevalence of family chain migration differ among major sending regions, and (2) how does the surge in late-age immigration since 1980 vary by source regions and major sending countries? Specifically, we derive age-specific migration multipliers for the major sending regions and the four top source countries. These nations also feature the largest backlogs for numerically capped family visas (Wasem 2012), which has implications for the age composition of sponsored relatives who age as they wait for visas in multi-year queues. In addition to improving on prior estimates of chain migration, our analyses clarify why the age composition of the foreign stock population from Asia and Latin America diverged (He 2002; Grieco et al. 2012). Before describing the data and estimation methods we provide a brief overview of the logic that led to Congress’s gross miscalculation of the impact of the 1965 Amendments on the regional origins of US immigrants. The concluding section discusses the implications of family chain migration in the context of an aging society and contemplated comprehensive reform