Molecular Differentiation Within and Between Eucalyptus risdonii, E. amygdalina and Their Hybrids Using RAPD Markers

Abstract

Random amplified polymorphic DNA (RAPD) studies of a natural hybrid swarm between Eucalyptus amygdalina Labill. and E. risdonii Hook.f. and nearby allopatric stands revealed that, despite clear morphological differences, all bands were shared between species. However, frequency differences revealed genetic divergence between species, populations within species, and individuals within populations. Variation was greatest between individuals within populations and lowest between species. For both species, the direction of variation which distinguished the two populations was in a different direction to that which separated the two species, suggesting population differences were not due to introgression but were the result of genetic isolation and/or strong localised selection. Several morphologically typical individuals with intermediate RAPD profiles were detected in the hybrid swarm and nearby allopatric samples of both species, suggesting that some cryptic introgression may be occurring. Controlled F1 crosses generally had closer genetic affinity to E. risdonii, raising the possibility that some parents used may have been advanced generation hybrids. While natural hybrids selected for their intermediate leaf phenotype were usually also intermediate between the two species using RAPD markers, some deviated markedly toward E. risdonii. The study suggests that morphological appearance does not necessarily reflect genetic (RAPD) status and in some cases detectable RAPD differences between spatially close populations of the same species may be as great or greater than the differences between species.

Interspecific Hybridization within Eucalyptus (Myrtaceae): Subgenus Symphyomyrtus, Sections Bisectae and Adnataria

“…Hybridization within eucalypts is often difficult to verify, as many naturally occurring and some spontaneously generated garden hybrids are observed as single individuals, often of uncertain parentage (e.g., Grayling and Brooker 1996;Rossetto et al 1996;Delaporte et al 2001), and where there is often evidence, either morphological or genetic, of backcrossing resulting in the offspring more resembling one of the parent species (Jordan et al 1993;Potts and Jordan 1994;Sale et al 1996;Jackson et al 1999;Shelbourne et al 1999). The long time to flowering can also make the morphological assessment of hybridity in offspring difficult or, at best, a long-term prospect, especially where there are longer-term problems with hybrid fitness and survival (Lopez et al 2000) or where the ratio of male to female parental dominance alternates within the first few years (Bouvet andVigneron 1995, 1996), although predictive parental contribution based on multivariate morphological assessments is possible for some features (Baril et al 1997a(Baril et al , 1997b.…”

Genetic and morphological diversity in <i>Armeria</i> (Plumbaginaceae) is shaped by glacial cycles in Mediterranean refugia

“…This implies that ad-ditive patterns of such markers are expected in hybrids at the population level, and consequently they can be used to examine hybridization and introgression (e.g. Sale & al., 1996;Martin & Cruzan, 1999). RAPD phenotypes have been widely used to estimate the genetic structure of populations (Steward & Excoffier, 1996;Palacios & González Candelas, 1997;Jordano & Godoy, 2000;Segarra-Moragues & Catalán, 2003).…”

Natural Hybrid Zone of Aconitum Species in the Western Carpathians: Linnaean Taxonomy and ISSR Fingerprinting

“…Of the various analytic methods, genetic fingerprinting with hypervariable PCR markers is the most appropriate technique in plant population genetics studies (Bonin et al, 2007). ISSRs have been employed to detect hybrids in the Tasmanian endemics Eucalyptus richardsonii and E. amygdalina (Sale et al, 1996), to study two closely related Mexican oaks with partially overlapping distributions (González-Rodriguez et al, 2004), and to analyze black and red spruces and their hybrids (Nkongolo et al, 2003). Hybrids between closely related species, and hybrid zones, may be recognized based on morphological markers, but though very helpful they are not suited for detailed analyses (Minder et al, 2007).…”