Morphometric and isozyme evidence for the hybrid origin of a new tetraploid radiate groundsel in York, England

Abstract

A morphometric and isozyme analysis of a fertile tetraploid radiate groundsel discovered in York, England, in 1979, showed it to differ markedly from typical inland radiate groundsel, Senecio vulgaris var. hibernicus. Morphologically, York radiate groundsel was intermediate between S. vulgaris and S. squalidus plants derived from York and Edinburgh populations. In addition, it exhibited an additive esterase phenotype which combined the aEst-1 and flEst-1 phenotypes expressed by S. vulgaris and S. squalidus, respectively. In contrast, S. vulgaris var. hibernicus does not express a j3Est-1 allozyme. It is concluded that York radiate groundsel is a product of hybridization between S. vulgaris and S. squalidus quite different from that of S. vulgaris var. hibernicus. This new variant appears to be of very recent origin, it exhibits a high level of self seed set, and is currently relatively well established in the city of York. Despite its ability to intercross with typical S. vulgaris, it appears to have maintained its distinctive morphological and isozyme phenotype in the wild.

Plant introductions, hybridization and gene flow

“…hibernicus being introgressed. This is not wholly unexpected, as the two variants of S. vulgaris are very similar morphologically (Irwin & Abbott 1992). Consequently, very few genes of S. squalidus are likely to have been introgressed into S. vulgaris to produce var.…”

“…In addition, an allozyme marker, which is present at high frequency in S. squalidus but is absent from native allopatric populations of S. vulgaris, occurs at an intermediate frequency in the radiate variant . Artificial resynthesis and allozyme markers also provide evidence for S. vulgaris and S. squalidus being the parents of the tetraploid S. eboracensis (Irwin & Abbott 1992;Lowe & Abbott 2000), and the hexaploid S. cambrensis . The parentage of S. cambrensis has also been confirmed by the results of a survey of chloroplast and nuclear rDNA RFLPs (Harris & Ingram 1992;.…”

“…vulgaris, which produces discoid capitula containing only hermaphrodite disc florets. (ii) A tetraploid hybrid species, S. eboracensis Abbott & Lowe, first recorded in the British Isles at York in 1979 (Irwin & Abbott 1992) and still restricted to that locality (figure 1b). This species is intermediate to the two parent species in a range of morphological traits, but possesses some novel characters (Irwin & Abbott 1992;Lowe & Abbott 2003).…”

“…(ii) A tetraploid hybrid species, S. eboracensis Abbott & Lowe, first recorded in the British Isles at York in 1979 (Irwin & Abbott 1992) and still restricted to that locality (figure 1b). This species is intermediate to the two parent species in a range of morphological traits, but possesses some novel characters (Irwin & Abbott 1992;Lowe & Abbott 2003). (iii) An allohexaploid hybrid species, S. cambrensis Rosser, first discovered in Britain in 1948 near Wrexham, Wales (Rosser 1955) and since recorded at other sites in Wales as well as in Edinburgh (figure 1b).…”

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

“…During the course of its spread, S. squalidus has hybridized with the native tetraploid species, Senecio vulgaris L. (2n ϭ 40), and this has led to the recent origin of three recognized, sexually reproducing, hybrid taxa: an introgressant form of S. vulgaris, S. vulgaris var. hibernicus Syme ); a recombinant tetraploid hybrid species, S. eboracensis Abbott and Lowe (Irwin and Abbott 1992;Lowe and Abbott 2003); and an allohexaploid, S. cambrensis Rosser (Rosser 1955;Ashton and Abbott 1992).…”