Applications of Multiple Nuclear Genes to the Molecular Phylogeny, Population Genetics and Hybrid Identification in the Mangrove Genus <i>Rhizophora</i>

<div><p>The genus <i>Rhizophora</i> is one of the most important components of mangrove forests. It is an ideal system for studying biogeography, molecular evolution, population genetics, hybridization and conservation genetics of mangroves. However, there are no sufficient molecular markers to address these topics. Here, we developed 77 pairs of nuclear gene primers, which showed successful PCR amplifications across all five <i>Rhizophora</i> species and sequencing in <i>R</i>. <i>apiculata</i>. Here, we present three tentative applications using a subset of the developed nuclear genes to (I) reconstruct the phylogeny, (II) examine the genetic structure and (III) identify natural hybridization in <i>Rhizophora</i>. Phylogenetic analyses support the hypothesis that <i>Rhizophora</i> had disappeared in the Atlantic-East Pacific (AEP) region and was re-colonized from the IWP region approximately 12.7 Mya. Population genetics analyses in four natural populations of <i>R</i>. <i>apiculata</i> in Hainan, China, revealed extremely low genetic diversity, strong population differentiation and extensive admixture, suggesting that the Pleistocene glaciations, particularly the last glacial maximum, greatly influenced the population dynamics of <i>R</i>. <i>apiculata</i> in Hainan. We also verified the hybrid status of a morphologically intermediate individual between <i>R</i>. <i>apiculata</i> and <i>R</i>. <i>stylosa</i> in Hainan. Based on the sequences of five nuclear genes and one chloroplast intergenic spacer, this individual is likely to be an F1 hybrid, with <i>R</i>. <i>stylosa</i> as its maternal parent. The nuclear gene markers developed in this study should be of great value for characterizing the hybridization and introgression patterns in other cases of this genus and testing the role of natural selection using population genomics approaches.</p>