Molecular evidence for an extinct parent of the tetraploid species Microseris acuminata and M. campestris (Asteraceae, Lactuceae)

Abstract

The five tetraploid (2n = 36) species in the Californian genus Microseris illustrate three very different evolutionary scenarios.1 The perennial M. scapigera of Australia and New Zealand has arisen from a hybrid between an annual and a perennial species in North America after chromosome duplication and long-distance dispersal (Chambers 1955;Van Houten et al. 1993). Chloroplast DNA analysis (Wallace & Jansen 1990) suggests that the maternal parent of this hybrid was ancestral to the present-day annuals, and morphological evidence suggests that the paternal parent is related to the present-day M. borealis (Chambers 1955). M. scapigera therefore exemplifies the accidental arrival of a new genetic entity in a geographically isolated Keywords: chloroplast DNA, concerted evolution, extinct parent, ITS, Microseris, polyploids, RAPD 13 September 1996; revision received 23 January 1997; 4 February 1997 Molecular Ecology 1997 Figure 1, from Chambers (1955), summarizes the possible relationships among the various annuals. Recognition of the two tetraploid entities was a key factor in his analysis. Except for the strictly coastal species, M. bigelovii, the ecological differentiation among the Californian annuals of Microseris is very subtle and they occur frequently in mixed populations. Artificial hybrids among the diploids are at least partially fertile, and the distribution of chloroplast genomes is not congruent with the species borders (Roelofs & Bachmann 1995, 1997. Still, all of these species appear to retain their identity. ReceivedThe tetraploids may be as crucial to an understanding of factors involved in the origin and maintenance of the species listed under (3) as they were for the elucidation of their taxonomy. Molecular data provide new sources of evidence for polyploid evolution (Doyle et al. 1990;Soltis & Soltis 1993;Soltis et al. 1995;Lowe & Abbott 1996). This investigation was designed to use molecular data to determine the exact parentage of M. acuminata and M. campestris including evidence for a unique origin or a repeated local origin. This information is essential for a search for factors involved in the apparently stable coexistence of the ecologically similar Californian annuals of Microseris. agarose gels and blotted on to Qiabrane plus membranes. DNA digested with HinfI (four base-pair recognition site) was separated on 6% polyacrylamide sequence gels and electroblotted using the methodology described by Van Houten et al. (1993). Hybridization was performed with radioactively labelled Lettuce SacI chloroplast clones described by Jansen & Palmer (1987). PCR amplifications for RAPD analysis with DNA mini preparations from one leaf (Hombergen & Bachmann 1995) were performed with Super Taq polymerase (HT Biotechnologies) in a MJ Research PTC-100/96 thermal cycler as previously described (Roelofs & Bachmann 1995). Primer kits A, C and H from Operon Technologies (USA) were screened for reliably reproducible polymorphic RAPD markers. The amplification products were separated on 1.5% agarose gels and ...

Genome evolution of allopolyploids: a process of cytological and genetic diploidization

“…Similar results were also documented from other allopolyploid plants, including Microseris (van Houten et al, 1993;Roelofs et al, 1997), Saxifraga (Brochmann et al, 1996) and Paeonia (Sang et al, 1995;Zhang and Sang, 1999). In addition to the homogenization of an alternative rDNA repeat, the formation of novel rDNA types was also reported in Medicago (Cluster et al, 1996), Paeonia, and Microseris where novel rDNA types were recovered from gene-conversion events between alternative-repeat types.…”

Duplicated genes evolve independently after polyploid formation in cotton

“…Reciprocal recombination, gene conversion, and other forms of nonindependence among homoeologues remain evolutionary possibilities (20,24,51); however, the relative frequency of these outcomes and the sequences subject to each mechanism remain unknown. In this respect, it is noteworthy that nonindependence has already been demonstrated for highly repeated homoeologous sequences such as ribosomal arrays, in Gossypium as well as in other polyploids (20,(52)(53)(54)(55). The present results exemplify genic stasis accompanying polyploidization, providing a sharp contrast to the several recent examples of rapid genomic evolution in allopolyploids (25)(26)(27)56).…”

A plastid tree can bring order to the chaotic generic taxonomy of Rytidosperma Steud. s.l. (Poaceae)

“…Such low resolution could be the result of fixation of point mutations, i.e. homogenisation of hybrid sequences by the process of concerted evolution (Wendel et al, 1995;Roelofs et al, 1997;Fuertes Aguilar et al, 1999b). For that to apply low levels of variation among individual sequences would be expected but in fact observed ITS sequences are not particularly homogenous (Table 6) and we attribute low resolution to a simple paucity of parsimony informative characters given the number of taxa.…”