Molecular divergence between disjunct taxa in eastern Asia and eastern North America

Abstract

Eastern Asian‐eastern North American disjuncts in four genera were examined for allozyme divergence and sequence divergence of the internal transcribed spacers (ITS) of nuclear ribosomal DNA. The disjunct pairs of taxa include Caulophyllum robustum‐C. thalictroid.es, Menispermum dauricum‐M. canadense, Penthorum chinense‐P. sedoides, and Phryma leptostachya var. asiatica‐P. leptostachya var. leptostachya. Allozyme divergence was comparable in Caulophyllum and Penthorum (genetic identities of 0.534 and 0.546) and was considerably higher than between pairs of taxa in Menispermum (0.273) and Phryma (0.291). Caulophyllum and Penthorum, which have the highest genetic identities at allozyme loci, also have low ITS sequence divergences (1.30 and 1.65%, respectively). Phryma, which has low isozyme identity, also has the highest ITS sequence divergence (4.46%). The two taxa of Menispermum have low ITS sequence divergence (0.93%) despite having a low identity (0.273) at allozyme loci. The results suggest that divergence between the taxa in the four genera are not the result of a single historical event. Estimated divergence times are reasonably consistent with a late Miocene disjunction for Caulophyllum and Penthorum, whereas the age of the Phryma disjunction is calculated at over 20 million years. The nonconcordant divergences between allozymes and ITS sequences in Menispermum may be caused by concerted evolution in the latter or possibly longer generation time in the woody plants. Additional molecular data are needed to clarify the situation.

Intercontinental genetic divergence of Castanea species in eastern Asia and eastern North America

“…pumila in North America. Genetic divergence has been examined for several woody genera with disjunctions between eastern Asia and eastern North America, indicating a wide range in interspecific identities based on allozyme data: from I ¼ 0.273 between Merispermum dauricum and M. canadense (Lee et al, 1996) to I ¼ 0.434 between Liriodendron chinense and L. tulipifera (Parks and Wendel, 1990), and I ¼ 0.431 between Liquidambar formosana and L. styraciflua (Hoey and Parks, 1991) to I ¼ 0.712 between Magnolia officinalis var. biloba and M. tripetala (Qui et al, 1995) and I ¼ 0.809 between Magnolia officinalis var.…”

Phylogeny and biogeography of Sassafras (Lauraceae) disjunct between eastern Asia and eastern North America

“…Miq. (Wen 2000), Liquidambar L. (Hoey and Parks 1991, Shi et al 1998, Ickert-Bond and Wen 2006, Phryma L. (Lee et al 1996, Xiang et al 2000, Nie et al 2006a, and Symplocarpus R. A. Salisbury ex Nuttall (Wen et al 1996, Nie et al 2006b). Sassafras is one of the few representatives of Lauraceae with a disjunct distribution primarily in the north temperate zone extending into the subtropical regions in eastern Asia and eastern North America (Fig.…”

Relaxed molecular clocks for dating historical plant dispersal events

“…It is often more parsimonious to interpret the history of taxa with extended fossil records in a framework of continuity [11,12]. Yet, there is ample direct evidence of rapid species expansions following dispersal from the study of invasive species, phylogeographic molecular data, and natural experiments such as Krakatau, an island sterilized by a massive eruption in 1883 [13][14][15][16].The idea of dating the divergence of lineages from the time-dependent change of their genomes, the molecular clock hypothesis, is 40 years old [17], and plant geographers have applied sequence-or protein-based dating since the 1990s [18][19][20][21][22][23][24][25][26][27][28]. With increasing computer power and access to readily implemented molecular evolutionary…”

“…The idea of dating the divergence of lineages from the time-dependent change of their genomes, the molecular clock hypothesis, is 40 years old [17], and plant geographers have applied sequence-or protein-based dating since the 1990s [18][19][20][21][22][23][24][25][26][27][28]. With increasing computer power and access to readily implemented molecular evolutionary…”