Gene flow among different taxonomic units: evidence from nuclear and cytoplasmic markers in Cedrus plantation forests

Abstract

Hybridization and introgression are important natural evolutionary processes that can be successfully investigated using molecular markers and open- and controlled-pollinated progeny. In this study, we collected open-pollinated seeds from Cedrus atlantica, Cedrus libani and C. libani x C. atlantica hybrids from three French-plantation forests. We also used pollen from C. libani and Cedrus brevifolia to pollinate C. atlantica trees. The progeny were analyzed using three different types of molecular markers: RAPDs, AFLPs and cpSSRs. Chloroplast DNA was found to be paternally inherited in Cedrus from the progeny of controlled-crosses. Heteroplasmy, although possible, could not be undoubtedly detected. There was no indication of strong reproductive isolating barriers among the three Mediterranean Cedrus taxa. Gene flow between C. atlantica and C. libani accounted for 67 to 81% of viable open-pollinated seedlings in two plantation forests. We propose that Mediterranean Cedrus taxa should be considered as units of a single collective species comprising two regional groups, North Africa and the Middle East. We recommend the use of cpSSRs for monitoring gene flow between taxa in plantation forests, especially in areas where garden specimens of one species are planted in the vicinity of selected seed-stands and gene-conservation reserves of another species.

Relationships among Cedrus libani, C. brevifolia and C. atlantica as revealed by the morphological and anatomical needle characters

“…The possibility of hybridization (Fady et al 2003), together with recent results of cytological (Bou DagherKharrat et al 2001), isoenzymatic (Scaltsoyiannes 1999), AFLP (Bou Dagher-Kharrat et al 2007) and cpDNA and mtDNA phylogeny analyses (Qiao et al 2007) pointed out the close genetic relationships among Mediterranean cedar taxa and suggest for them the subspecific taxonomic rank. The studies on genetic diversity and phylogeography of C. atlantica (Terrab et al 2006(Terrab et al , 2008, genetic diversity of C. libani (Semaan and Dodd 2008) and C. brevifolia (Eliades et al 2011) described the high level of genetic variation and significant differences among studied populations of compared species.…”

High genetic diversity and significant population structure in Cedrus brevifolia Henry, a narrow endemic Mediterranean tree from Cyprus

“…Patterns of genetic variation were examined using two DNA marker types with different inheritance modes: biparentally inherited (nuclear microsatellites: Chaib et al 2006) and paternally inherited (chloroplast microsatellites: Fady et al 2003, who found that chloroplast DNA-referred to as ''plastid''-is paternally inherited in this genus). Attempts to detect variation at maternally inherited mitochondrial DNA failed due to lack of polymorphism (Eliades 2008).…”

Variation of selfing rate and inbreeding depression among individuals and across generations within an admixed Cedrus population

“…There are only a few studies that have estimated the individual selfing rates and ID under natural mating systems, by calculating the proportion of empty seeds and with biparentally inherited molecular markers such as isozymes, which need more complicated statistical estimators (Kärkkäinen and Savolainen, 1993;Ritland and Travis, 2004;Bower and Aitken, 2007). In this study, we took benefit of the high diversity and paternal inheritance of cpSSRs markers in Pinaceae species (Parducci et al, 2001;Ribeiro et al, 2002;Naydenov et al, 2005) and particular Cedrus (Fady et al, 2003;Terrab et al, 2006). In Cedrus, we measured a mean selfing rate circa 0.1, which is in agreement with the absence of incompatibility mechanisms and the values reported in other conifers (Franklin, 1969;Cottrell and White, 1995;Sorensen, 1999;Restoux et al, 2008).…”

“…DNA was extracted from 50 mg of fresh plant tissue using the Qiagen Extraction kit (Qiagen, Courtaboeuf, France). The PCRs were performed following the protocol by Fady et al (2003). Electrophoresis was conducted in an Li-Cor sequencer.…”

“…Molecular markers such as allozymes (Ritland and El-Kassaby, 1985) or microsatellite markers (Collevatti et al, 2001) have long been used for estimating the selfing rate in nature. In Cedrus, as in most Pinaceae species, the chloroplast genome is uni-parentally inherited from the male parent and does not recombine (Fady et al, 2003). Consequently, this provides an efficient tool to assess the probability of a selfing event by comparing the chloroplast genotypes of progenies and their seed trees.…”