Origins of the new allopolyploid species Senecio cambrensis (asteraceae) and its relationship to the canary islands endemic Senecio teneriffae

Abstract

The distribution of a 330 bp cpDNA insertion was reexamined in British material of Senecio cambrensis (2n = 6x = 60), its two putative parental taxa, S. squalidus (2n = 2x = 20) and S. vulgaris (2n = 4x = 40), and the closely related Canary Islands' endemic S. teneriffae (2n = 6x = 60). This formed part of a test of the hypothesis that the Welsh form of S. cambrensis is derived from introduced S. teneriffae rather than having originated in Wales via allopolyploidy as previously supposed. It was established that the 330 bp insertion was carried by all plants of Welsh S. cambrensis and also S. teneriffae, but was absent from the cpDNA of Edinburgh S. cambrensis and all plants of British S. squalidus and S. vulgaris var. vulgaris surveyed. However, two of 19 individuals tested of S. vulgaris var. hibernicus also possessed the cpDNA insertion, indicating that it is present in British material of S. vulgaris, although at low frequency. The close similarity between S. teneriffae and S. cambrensis, especially the Welsh form of S. cambrensis, was confirmed by the results of a restriction analysis of rDNA, and also morphometric and crossing studies. However, isozyme analysis showed that S. teneriffae is monomorphic for βEST‐3 and ACO‐1 phenotypes that are not present in Welsh and Edinburgh S. cambrensis, nor in S. squalidus and S. vulgaris material surveyed. It is concluded that S. teneriffae and S. cambrensis are two closely related allohexaploid taxa that have very similar, but different origins. It is postulated that whereas S. cambrensis (in Wales and Edinburgh) is the allohexaploid of S. vulgaris and S. squalidus, S. teneriffae is possibly the allohexaploid of S. vulgaris and S. glaucus, the latter being a diploid species closely related to S. squalidus.

Gene conversion events and variable degree of homogenization of rDNA loci in cultivars ofBrassica napus

“…However, three cultivars (‘Norin 9’, ‘Asparagus kale’ and ‘Yudal’) retained a high number of C-genome genes, indicating that the process may still be in progress, as in some recently formed natural allopolyploid populations of Senecio (Lowe and Abbott, 1996), Tragopogon (Kovarik et al , 2005) and Cardamine (Zozomova-Lihova et al , 2014). No apparent relationship between copy number variation and plastid haplotypes was found, indicating that the putative polyphyletic origin plays little or no role in homogenization direction or that breeding schemes crossing the different cultivars did not allow us to identify the origin.…”

Ecological Factors Influencing Tetraploid Speciation in Snow Buttercups (Ranunculus Adoneus): Niche Differentiation and Tetraploid Establishment

“…Between 30% and 70% of flowering plants have multiple copies of chromosomes (Stebbins 1951;Grant 1971;Masterson 1994), and at least 2-4% of the speciation events in angiosperms have involved chromosome doubling rather than diversification of already polyploid lineages (Otto and Whitton 2000). New polyploid taxa have been observed in the past century, such as Tragopogon mirus and T. miscellus (Asteraceae; Ownbey 1950); Senecio cambrensis (Asteraceae; Lowe and Abbott 1996); and Spartina anglica (Poaceae; Thompson 1991), demonstrating that polyploid speciation is an ongoing source of diversity.…”

Interspecific hybridization and the origin of new plant taxa in Scotland

“…All Scottish material examined contained a cpDNA haplotype denoted as A while all Welsh material surveyed possessed cpDNA haplotype C (Lowe & Abbott, 1996). As these two cpDNA haplotypes are also possessed by British material of S. vulgaris, but not by British S. squalidus (Lowe & Abbott, 1996), it was concluded that Edinburgh and Welsh forms of S. cambrensis are derived from different maternal parents. (Harris (1990) has shown that cpDNA is inherited maternally in Senecio.…”

“…1). However, single character analysis (by one-way ANOVA, see Lowe & Abbott, 1996)) showed that Edinburgh and Welsh S. cambrensis differed significantly in mean for 10 of the 26 characters recorded. Most notably, Edinburgh S. cambrensis had longer capitula and calyculus bracts, longer ray florets, larger leaves, greater self-seed set and a greater number of ray florets and pores per pollen grain.…”

“…This discovery raised questions as to its origin at this location. To determine whether S. cambrensis had arisen separately in Wales and Scotland, surveys of isozyme and chloroplast DNA variation have been conducted in samples of the species and its two parents from North Wales and Edinburgh 1992; Lowe & Abbott, 1996). It was established that at two enzyme encoding loci (Acp-2 and e~Est-1) S. cambrensis from North Wales exhibited a different enzyme phenotype compared with plants from Edinburgh (Table 1).…”