Genetic variation and phylogeographic analyses of two species of Carpobrotus and their hybrids in California

Abstract

Despite the commonality and study of hybridization in plants, there are few studies between invasive and noninvasive species that examine the genetic variability and gene flow of cytoplasmic DNA. We describe the phylogeographical structure of chloroplast DNA (cpDNA) variation within and among several interspecific populations of the putative native, Carpobrotus chilensis and the introduced, Carpobrotus edulis (Aizoaceae). These species co-occur throughout much of coastal California and form several 'geographical hybrid populations'. Two hundred and thirty-seven individuals were analysed for variation in an approximate 7.0 kb region of the chloroplast genome using PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism) data. Phylogenetic analyses and cpDNA population differentiation were conducted for all morphotypes. Historic geographical dispersion and the coefficient of ancestry of the haplotypes were determined using nested clade analyses. Two haplotypic groupings (I and II) were represented in C. chilensis and C. edulis, respectively. The variation in cpDNA data is in agreement with the previously reported allozyme and morphological data; this supports relatively limited variation and high population differentiation among C. chilensis and hybrids and more wide-ranging variation in C. edulis and C. edulis populations backcrossed with C. chilensis. C. chilensis disproportionately contributes to the creation of hybrids with the direction of gene flow from C. chilensis into C. edulis. The cpDNA data support C. chilensis as the maternal contributor to the hybrid populations.

Does intraspecific hybridization contribute to the evolution of invasiveness?: an experimental test

“…Finally, hybridization and admixture that occurs in the introduced range among previously isolated native range populations might also result in genetic differentiation and evolution (Ellstrand and Schierenbeck 2000;Kolbe et al 2004). Relative to the role of natural selection, drift and hybridization have received less attention in the invasions literature (but see Vila and D'Antonio 1998;Gaskin and Schaal 2002;Facon et al 2005;Schierenbeck et al 2005).…”

Enhanced frugivory on invasive Silene latifolia in its native range due to increased oviposition

“…First, drift and founder effects might have led to a different genetic set-up of native versus introduced plants (Taylor & Keller 2007). Second, in the introduced range, plants from previously isolated populations could have hybridized and this might have led to genotypes exhibiting novel traits associated with invasiveness (Vila & D'Antonio 1998;Schierenbeck et al 2005;Wolfe et al 2007). The third explanation for genetic differences is that selection processes in the introduced range are different from those in the native range due to changed ecological interactions such as the release from their natural enemies.…”

Gene flow between introduced and native Eucalyptus species: Flowering asynchrony as a barrier to F1 hybridisation between exotic E. nitens and native Tasmanian Symphyomyrtus species

“…Pollen-mediated gene flow from exotic plant species can result in the introgression of exotic genes into native gene pools and the dilution or contamination of ''pure'' native species (Rhymer and Simberloff, 1996;Vila et al, 2000;Schierenbeck et al, 2005). Such exotic gene flow occurs through F 1 hybridisation and successive backcrossing (Levin, 1978;Arnold, 1997), and is recognised as a significant threat to many native plant species around the world (Rhymer and Simberloff, 1996;Ellstrand et al, 1999;Vila et al, 2000).…”