Hybrid Tamarix widespread in U.S. invasion and undetected in native Asian range

Abstract

Biological invasions are drastically altering natural habitats and threatening biodiversity on both local and global levels. In one of the United States' worst invasions, Eurasian Tamarix plant species have spread rapidly to dominate over 600,000 riparian and wetland hectares. The largest Tamarix invasion consists of Tamarix chinensis and Tamarix ramosissima, two morphologically similar species. To clarify the identity, origins, and population structuring of this invasion, we analyzed DNA sequence data from an intron of a nuclear gene, phosphoenolpyruvate carboxylase (PepC). This intron proved to be highly variable at the population level, and the 269 native and invasive specimens yielded 58 haplotypes, from which we constructed a gene genealogy. Only four of these haplotypes were common to both the U.S. and Eurasia. Surprisingly, we found that the most common plant in this U.S. invasion is a hybrid combination of two species-specific genotypes that were geographically isolated in their native Eurasian range. Less extensive hybrids exist in the invasion, involving combinations of T. ramosissima and T. chinensis with Tamarix parviflora and Tamarix gallica. The presence of potentially novel hybrids in the U.S. illustrates how importation of exotics can alter population structures of species and contribute to invasions.

Meiotic behaviour, karyotype analyses and pollen viability in species ofTamarix(Tamaricaceae)

“…The unpublished molecular studies on natural populations in Iran (Akhani & Borsch, in prep. ) and previous molecular investigations (Gaskin 2003b;Gaskin & Schaal 2002, 2003Gaskin & Shafroth 2005) have shown a high ability of hybridization in natural and invasive populations of Tamarix. Hybridization is advantageous as a potentially adaptive evolutionary factor, which can stabilize different types of variation, such as evolutionary novelty, genetic variation and fixed heterosis, and could stimulate the evolution of invasiveness (Ellstrand & Schierenbeck 2000).…”

Estimating the species tree for Hawaiian Schiedea (Caryophyllaceae) from multiple loci in the presence of reticulate evolution

“…These included portions of three low-copy nuclear genes: chloroplast-expressed glutamine synthetase (ncpGS), nitrate reductase (NIA), and the fourth intron of phosphoenolpyruvate carboxylase (PepC) and eight noncoding regions of the chloroplast genome, selected for their relatively high variability in other angiosperms: six intergenic regions (petN-psbM, psbE-petL, psbM-trnD, trnD-trnT, and trnQ-rpS16); a portion of the tRNA-Lys (trnK) intron with primers in 5 0 trnK and 5 0 matK; a portion of the trnK intron with primers in 3 0 matK and 3 0 trnK; and the RPS16 intron. PCR primers were previously published (Demesure et al, 1995;Emshwiller and Doyle, 1999;Gaskin and Schaal, 2002;Howarth and Baum, 2002;Johnson and Soltis, 1994;Lee and Wen, 2004;Popp et al, 2005;Popp and Oxelman, 2001;Shaw et al, 2005Shaw et al, , 2007 or designed for this study (Supplementary Table S1). …”

Erosional Consequence of Saltcedar Control

“…The most prevalent introduced riparian trees in the western United States are saltcedar (Tamarix chinensis, T. ramosissima and hybrids) (Gaskin and Schaal 2002) and Russian olive (Elaeagnus angustifolia L.) (Katz and Shafroth 2003). These species have become the second and fifth most abundant lowland riparian trees in the interior western United States (Friedman and others 2005a), occupying several hundred thousand hectares (Zavaleta 2000).…”