Phylogeographic breaks within Asian butternuts indicate the existence of a phytogeographic divide in East Asia

Abstract

Summary East Asia has been hypothesized to be subdivided into two distinct northern and southern areas, separated by a band of dry climate that was far more severe in the early Tertiary but still exists today. However, this biogeographic hypothesis has rarely been tested using a molecular phylogeographic approach. We genotyped 70 populations throughout the distributional range of Asian butternuts (Juglans section Cardiocaryon) using eight chloroplast DNA regions, one single‐copy nuclear gene, and 17 nuclear microsatellite loci, supplemented with paleodistribution modeling of the major genetic clades. The genetic data consistently identified two clades, one northern, comprising Juglans mandshurica and Juglans ailantifolia, and one southern, comprising Juglans cathayensis. The two clades diverged through climate‐induced vicariance of an ancestral northern range during the mid‐Miocene and remained mostly separate thereafter, with geographical isolation of the Japanese Islands and refugial isolation or secondary contacts in the late Pleistocene producing further subdivision within the northern clade. But beyond all that, we also discovered a role of environmental adaptation in maintaining and/or reinforcing the north–south divergence. Asian butternuts offer a strong case for the existence of a biogeographic divide between the northern and southern parts of East Asia during the Neogene and into the Pleistocene.

Phylogeography of postglacial range expansion in Juglans mandshurica (Juglandaceae) reveals no evidence of bottleneck, loss of genetic diversity, or isolation by distance in the leading-edge populations

“…Unfortunately, we failed to detect polymorphisms other than those already detected in Bai et al (2016).…”

“…Approximately 7 to 30 Manchurian walnut trees were sampled from each population for nSSR loci analysis. Genotypes of the DNA samples were scored using 17 pairs of the microsatellite PCR primers that were used in Bai et al (2016). The SSR genotyping procedures are found in Bai et al (2016).…”

“…In addition to sequencing the eight chloroplast fragments used in Bai et al (2016), we sequenced six regions that were used for Juglans cinerea in Laricchia et al (2015) (atpI-rps2, ndhK-ndhC, psaA-trnS, rpoB-rpoC1, trnH-trnK, trnV-rbcL) for 10 samples per population (individuals > 30). Unfortunately, we failed to detect polymorphisms other than those already detected in Bai et al (2016).…”

“…Manchurian walnut is distributed parapatrically with Chinese walnut (J. cathayensis), a closely related species in subtropical mainland China. The two walnut species met and cross-fertilized in North China, resulting in a broad hybrid zone (Bai et al, 2016). To avoid any confounding effects of hybridization, the seemingly admixed populations located in North China were excluded from the present investigation.…”

Long‐distance dispersal or postglacial contraction? Insights into disjunction between Himalaya–Hengduan Mountains and Taiwan in a cold‐adapted herbaceous genus, Triplostegia

“…2.15 Ma, 95% HPD: 0.50–5.30 Ma; node V in Figure 4) and previously studied woody plants ( c . 4.04 Ma, Juglans cathayensis , Bai, Wang, & Zhang, 2015; c . 3.31 Ma, Taiwania cryptomerioides , Chou, Thomas, Ge, LePage, & Wang, 2011; c .…”