Population Structure and Genetic Diversity in the Natural Distribution of Neolamarckia cadamba in China

Abstract

Neolamarckia cadamba (Roxb.) Bosser is a fast-growing deciduous tree species and belongs to the Neolamarckia genus of the Rubiaceae family. This species has great economic and medical values in addition to being an important timber species for multiple industrial purposes. However, few studies have examined the genetic diversity and population structure in the natural distribution of this species in China. Here, we applied both the haploid nrDNA ITS (619 bp for aligned sequences) and mtDNA (2 polymorphic loci) markers to investigate 10 natural populations (239 individuals in total) that covered most of the distribution of the species in China. The results showed that the nucleotide diversity was π = 0.1185 ± 0.0242 for the nrDNA ITS markers and π = 0.00038 ± 0.00052 for the mtDNA markers. The haplotype diversity for the mtDNA markers was h = 0.1952 ± 0.2532. The population genetic differentiation was small (Fstn = 0.0294) for the nrDNA ITS markers but large (Fstm = 0.6765) for the mtDNA markers. There were no significant effects of isolation by distance (IBD), by elevation, and by two climatic factors (annual average precipitation and tem perature). A geographic structure among populations (Nst<Gst) was absent. Phylogenetic analysis showed a highly genetic mixture among individuals of the ten populations. Pollen flow was substantially greater than seed flow (mp/ms ≫ 1.0) and played a dominant role in shaping population genetic structure. The nrDNA ITS sequences were neutral and all local populations did not undergo demographic expansion. The overall results provide fundamental information for the genetic conservation and breeding of this miraculous tree.

A Community-Based Framework Integrates Interspecific Interactions into Forest Genetic Conservation

“…Another viewpoint is to use the evolutionarily significant unit in conservation, which refers to monophyly regarding mtDNA variation or populations with significant population genetic differentiation in nuclear genome variation. Both units are based on population genetic differentiation, which often shows a contrasting pattern of population genetic structure, such as in the T. ciliata complex [3] and Neolamarckia cadamba [28]. Here, inconsistency could occur in delineating units regarding neutral molecular markers and adaptive phenotypic traits or in gene expression differences from transcriptome analysis [53].…”

“…The population genetic theory emphasizes the intraspecific interaction among genotypes, and its approach is widely applied to instructing genetic conservation [3,28]. The basic evolutionary processes that maintain genetic diversity involve selection, genetic drift, migration, and mutation at the population level [29].…”