Low genetic diversity and significant population structuring in the relict Amentotaxus argotaenia complex (Taxaceae) based on ISSR fingerprinting

Abstract

Amentotaxus, a genus of the Taxaceae, represents an ancient lineage that has long existed in Eurasia. All Amentotaxus species experienced frequent population expansion and contraction over periodical glaciations in Tertiary and Quaternary. Among them, Amentotaxus argotaenia complex consists of three morphologically alike species, A. argotaenia, Amentotaxus yunnanensis, and Amentotaxus formosana. This complex is distributed in the subtropical region of mainland China and Taiwan where many Pleistocene refugia have been documented. In this study, genetic diversity and population structuring within and between species were investigated based on the inter-simple sequence repeats (ISSR) fingerprinting. Mean genetic diversity within populations was estimated in three ways: (1) the percentage of polymorphic loci out of all loci (P) (2) Nei's unbiased expected heterozygosity (He), and (3) Shannon's index of phenotypic diversity. For a total of 310 individuals of 15 populations sampled from the three species, low levels of ISSR genetic variation within populations were detected, with P=4.66-16.58%, He=0.0176-0.0645 and Hpop=0.0263-0.0939, agreeing with their seriously threatened status. AMOVA analyses revealed that the differences between species only accounted for 27.38% of the total variation, whereas differences among populations and within populations were 57.70 and 14.92%, respectively, indicating substantial isolation between the patch-like populations. A neighbor-joining tree identified a close affinity between A. yunnanensis and A. formosana. Genetic drift due to small population size, plus limited current gene flow, resulted in significant genetic structuring. Low levels of intra-populational genetic variation and considerable inter-populational divergence were also attributable to demographic bottlenecks during and/or after the Pleistocene glaciations.

Population size, center–periphery, and seed dispersers’ effects on the genetic diversity and population structure of the Mediterranean relict shrub Cneorum tricoccon

“…Relict species are generally expected to show low levels of genetic diversity and strong population structure (Awad, Fady, Khater, Roig, & Cheddadi, 2014; Bauert, Kalin, Baltisberger, & Edwards, 1998; Ge et al., 2005) because they are usually composed of small, geographically isolated populations (Dobrowski, 2011; Hampe & Petit, 2005). However, experimental evidence has not always supported this generalization (see Peakall, Ebert, Scott, Meagher, & Offord, 2003; Vanden‐Broeck et al., 2011).…”

Species Occurrence, Hybridization and Speciation in Postglacial East and South Asia

“…The ancestral populations of T. radicans were able to migrate across the Bering Straits via a land bridge connection between North America and Asia. After that, the ancestral population separated into two paths: one from Sakhalin to Japan or via the Korean Peninsula to Japan, and one from the north to the south via Siberia which then separated into several paths of scattered refugia in Yunnan, Szechwan, Guizhou, Hunan, Hubai, Fujian and Taiwan (cf Lu et al 2001;Ge et al 2005). The genetic drift effected those isolated populations and promoted the process of speciation in various geographic regions.…”

“…The field relies on inferences that are made from macrofossils and pollen in sediment profiles and molecular evidence that can reveal aspects of history, such as the location of cryptic refugia (cf. Ge et al, 2005). Few paleoecological studies have identified the pollen and fossils of tree species.…”

Genetic Diversity of the Relict Plant Taiwania cryptomerioides Hayata (Cupressaceae) in Mainland China

“…These include Cathaya argyrophylla (GE et al, 1998), Ametotaxus argotaenia (GE et al, 2005), Glyptostrobus pensilis (LI and XIA, 2005), Metasequoia glyptostroboides , Cupressus chengiana (HAO et al, 2006), Torreya jackki (LI and JIN, 2007) and Abies ziyuanensis (TANG et al, 2007) (Table 4). Since these species are characterized by their relict status, biogeographic history may play an important role in determining their genetic diversity.…”

“…Many species that became extinct elsewhere survived in this region, but in a state of isolation and in small populations. Strong genetic differentiation has been discovered in some relict conifer species in China, for example Cathaya argyrophylla (GE et al, 1998), Glyptostrobus pensilis (LI and XIA, 2005), Metasequoia glyptostroboides and Ametotaxus argotaenia (GE et al, 2005). The genetic diversity of T. cryptomerioides from Taiwan has been assessed previously by allozyme (LIN et al, 1993), ISSR and ITS sequence analysis (CHANG, 2005).…”