Morphological and molecular evidence of natural hybridization in Shorea (Dipterocarpaceae)

Abstract

Shorea (Dipterocarpaceae) is a large genus in which many closely related species often grow together in Southeast Asian lowland tropical rain forests. Many Shorea species share common pollinators, and earlier studies suggested occurrence of interspecific hybridization and introgression. Here, we show morphological and molecular evidence of hybridization between Shorea species. In the census of all the trees of Shorea curtisii, Shorea leprosula, and Shorea parvifolia (>30 cm dbh) within the 164-ha area of Bukit Timah Nature Reserve in Singapore, we found 21 morphologically recognizable hybrid individuals. All of the putative hybrids could be distinguished obviously from the parental species on the basis of vegetative characters. Population genetic analysis of DNA sequences of two nuclear (GapC and PgiC) and chloroplast (trnL-trnF) regions demonstrated that each of the three species had several species-specific mutations. The nuclear sequences of the putative hybrids were heterozygote at all the speciesspecific sites between two parental species. Hybrid between S. curtisii and S. leprosula was found most, while S. curtisii × S. parvifolia and S. leprosula × S. parvifolia hybrids were also found. Almost no shared polymorphism between populations of the parental species suggests rarity of introgression. The study indicated that natural hybridization between sympatric Shorea species should not be uncommon, but all of the hybrid individuals were F 1 , and the post-F 1 hybrids were considerably rare.

Demographic History of Shorea curtisii (Dipterocarpaceae) Inferred from Chloroplast DNA Sequence Variations

“…From each population, material from 16 to 20 individuals were collected, except Bukit Larut and Lumut from which only seven and four individuals were obtained, respectively (Table 1). DNA samples from the Bukit Timah population used in this study were the same as those used by Kamiya et al (2011). The distance between sampled mother trees (or their saplings) was kept at 50 m or more to avoid the collection of half-sibs.…”

“…In Lambir Hills, samples from 20 mature individuals > 30 cm diameter at breast height (dbh) were collected from the 52-ha ecologic-research plot (Lee et al 2002a). DNA samples from the Bukit Timah population used in this study were the same as those used by Kamiya et al (2011). Total DNA was extracted from fresh or dried tissue using the DNeasy Plant Mini Kit (QIAGEN, Valencia, California, U.S.A.) or a modified CTAB procedure implemented by Tsumura et al (1996).…”

Species diversity and reticulate evolution in the Asplenium normale complex (Aspleniaceae) in China and adjacent areas

“…In order to detect reticulation in the A. normale complex, we employed a biparentally inherited marker, the single-copy nuclear gene pgiC. The pgiC gene has recently been successfully used in several phylogenetic studies of hybridization in ferns as well as in flowering plants (Russel & al., 2010;Juslen & al., 2011;Kamiya & al., 2011;Dyer & al., 2012;Sessa & al., 2012;Wang & al., 2012). Additionally, ploidy levels of the samples were determined by measuring spore size (Barrington & Paris, 1986) and determining DNA C-values by flow-cytometric analysis of selected specimens (Dolezel & al., 2007).…”

Introgression across evolutionary scales suggests reticulation contributes to Amazonian tree diversity

“…Indeed, it was previously 460 suggested that inter-specific hybrids between rainforest tree species are poor competitors, and that 461 fertile hybrid populations are nearly non-existent (Ashton 1969). While there is some evidence of 462 introgression in tropical trees (Scotti-Saintagne et al, 2013), most available studies substantiating this 463 are based on trees from other tropical regions or habitats (e.g., Shorea in Asia (Kamiya et al, 2011;464 Kenzo et al, 2019), or Rhizophora in Indo-Pacific mangroves (Lo 2010)). Many of these other 465 instances appear to occur only in degraded habitats, or involve infertile first-generation hybrids with 466 minimal backcrossing, which contrasts with the findings of our study.…”