Documentation of reticulate evolution in peonies (Paeonia) using internal transcribed spacer sequences of nuclear ribosomal DNA: implications for biogeography and concerted evolution.

Su, Tao; Crawford, Daniel J.; Stuessy, Tod F.

doi:10.1073/pnas.92.15.6813

Cited by 548 publications

(409 citation statements)

References 23 publications

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“…In contrast, recombinant ITS types have been observed in allopolyploid systems with regular meiosis (Buckler et al, 1997;Franzke and Mummenhoff, 1999;Nieto Feliner et al, 2004;Kovarik et al, 2005). The situation here may resemble that of paeonia hybrids, which frequently undergo vegetative reproduction and whose ITSs have retained much of the parental features (Sang et al, 1995). Together, the absence or reduced frequency of extensive interlocus homogenization is likely to be a consequence of the non-symmetrical meiosis in dogroses, which prevents meiotic recombination of univalent chromosomes.…”

Section: Discussionmentioning

confidence: 67%

Frequent silencing of rDNA loci on the univalent-forming genomes contrasts with their stable expression on the bivalent-forming genomes in polyploid dogroses (Rosa sect. Caninae)

et al. 2009

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The polyploid species in Rosa section Caninae (2n ¼ 21, 28 or 35) are characterized by an unusual reproductive system known as odd (or asymmetric) meiosis. Only two chromosome sets form bivalents in meiosis, whereas the remaining chromosomes are transmitted as univalents through the female germline. Evolution of ribosomal rRNA genes (rDNA) does not seem to be significantly affected by interlocus homogenization in dogroses. As a consequence, most species contain several rDNA families falling into two main clades (b and g) thought to be differentially distributed between bivalent and univalent chromosomes, respectively. Here, we have investigated expression of rRNA gene families in five pentaploid species (R. canina, R. rubiginosa, R. dumalis, R. sherardii and R. caesia, 2n ¼ 35) and in one tetraploid (R. mollis, 2n ¼ 28). Using extensive sequencing of ITS clones and cleaved amplified polymorphism sequence (CAPS) analysis, we found that the b-family was constitutively expressed in all species. However, there was large variation in the expression patterns of families constituting the g-clade. In addition, a single family can be active in one species, whereas silenced in another. The data show that the families on bivalent-forming chromosomes dominate rDNA expression in all dogrose species. We hypothesize that genes on bivalent genomes are stably expressed, whereas those on univalent genomes undergo variable levels of epigenetic silencing. Nonetheless, mosaic expression of univalent genomes could contribute to phenotypic variation between the species.

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Section: Discussionmentioning

confidence: 67%

Frequent silencing of rDNA loci on the univalent-forming genomes contrasts with their stable expression on the bivalent-forming genomes in polyploid dogroses (Rosa sect. Caninae)

et al. 2009

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“…In Caulerpa racemosa, Fama a et al (2000) and Durand et al (2002) revealed considerable intra-individual ITS sequence variation and the latter authors also showed conflict between trees inferred from the insert and ones from the ITS regions, all suggestive of hybridization events. Ribosomal RNA coding regions are particularly prone to introgression (Nichols, 2001;Riseberg and Wendel, 1993;Sang et al, 1995;Wendel et al, 1995) because of their multi-copy nature (Jorgensen and Cluster, 1988).…”

Section: Sequence Comparisons and Phylogenetic Analysesmentioning

confidence: 99%

Molecular systematics, historical ecology, and phylogeography of Halimeda (Bryopsidales)

Kooistra

Coppejans

Payri

2002

Molecular Phylogenetics and Evolution

124

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Halimeda (Bryopsidales), a genus of calcified, segmented green seaweeds, abounds in reefs and lagoons throughout the tropics. To investigate phylogenetic, phylogeographic, and historic ecological relationships of the genus, the nuclear rDNA including the SSU and both ITS regions were sequenced. A maximum likelihood tree revealed the following: (1) there were anatomical and morphological synapomorphies for five well-supported lineages; (2) the last common ancestor of one lineage invaded sandy substrata; those of two other lineages established in wave-affected habitats, whereas the cenancestor of the remaining two lineages occupied sheltered rocky slopes. Yet, several species adapted to new habitats subsequently, resulting in several cases of convergence; (3) all lineages separated into Atlantic and Indo-Pacific daughters, likely resulting from the rise of the Panamanian Isthmus. Each daughter pair gave rise to additional convergent species in similar habitats in different oceans; (4) Halimeda opuntia, the only monophyletic pantropical species detected so far, dispersed from the Indo-Pacific into the Atlantic well after the closure event; (5) minor SSU-sequence differences across species and phylogeographic patterns of vicariance indicated a relatively recent diversification of the extant diversity. Cretaceous and Early Tertiary fossil look-alikes of modern species must then have resulted from iterative convergence. Ó

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“…Empirical data indicate that species have arisen in this manner (e.g. Arnold, Hamrick & Bennett, 1990, Wang et al, 1990Arnold et al, 1993 ;Wang & Szmidt, 1994 ;Sang, Crawford & Stuessy, 1995 ;Wolfe, Xiang & Kephart, 1997), but experimental and theoretical studies have focused on the strict recombinational model, which involves the sorting of genic and chromosomal sterility factors. Because hybrid speciation is both reticulate and rapid, it is particularly amenable to experimental manipulation and replication.…”

Section: Hybrid Speciationmentioning

confidence: 99%

Plant hybridization

1998

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Summary 599 I. Introduction 599 II. Concepts and terminology 600 III. Historical background 600 IV. Studies of experimental hybrids 601 1. Isolating mechanisms 601 2. Prezygotic barriers 602 (a) Gametic barriers to hybridization 602 3. Postzygotic barriers 603 (a) Chromosomal rearrangements 604 (b) Genic sterility or inviability 604 4. Hybrid vigour 605 5. Introgression 606 6. Hybrid speciation 607 V. Experimental manipulations of natural hybrid populations 609 1. Hybrid‐zone formation 610 2. Pollinator‐mediated selection 610 3. Habitat selection 612 VI. The biology of different classes of hybrids 612 1. Character expression 613 (a) Morphological characters 613 (b) Chemical characters 613 (c) Molecular characters 613 2. The fitness of different classes of hybrids 614 (a) The importance of variance 614 (b) Estimating hybrid fitness 615 3. Interactions with parasites and herbivores 616 4. Patterns of mating 617 (a) Outcrossing rate 617 (b) Hybridization frequency 618 (c) Mate choice 618 VII. Conclusions and future research 619 Acknowledgements 620 References 620 Most studies of plant hybridization are concerned with documenting its occurrence in different plant groups. Although these descriptive, historical studies are important, the majority of recent advances in our understanding of the process of hybridization are derived from a growing body of experimental microevolutionary studies. Analyses of artificially synthesized hybrids in the laboratory or glasshouse have demonstrated the importance of gametic selection as a prezygotic isolating barrier; the complex genetic basis of hybrid sterility, inviability and breakdown; and the critical role of fertility selection in hybrid speciation. Experimental manipulations of natural hybrid zones have provided critical information that cannot be obtained in the glasshouse, such as the evolutionary conditions under which hybrid zones are formed and the effects of habitat and pollinator‐mediated selection on hybrid‐zone structure and dynamics. Experimental studies also have contributed to a better understanding of the biology of different classes of hybrids. Analyses of morphological character expression, for example, have revealed transgressive segregation in the majority of later‐generation hybrids. Other studies have documented a high degree of variability in fitness among different hybrid genotypes and the rapid response of such fitness to selection – evidence that hybridization need not be an evolutionary dead end. However, a full accounting of the role of hybridization in adaptive evolution and speciation will probably require the integration of experimental and historical approaches.

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Documentation of reticulate evolution in peonies (Paeonia) using internal transcribed spacer sequences of nuclear ribosomal DNA: implications for biogeography and concerted evolution.

Cited by 548 publications

References 23 publications

Frequent silencing of rDNA loci on the univalent-forming genomes contrasts with their stable expression on the bivalent-forming genomes in polyploid dogroses (Rosa sect. Caninae)

Frequent silencing of rDNA loci on the univalent-forming genomes contrasts with their stable expression on the bivalent-forming genomes in polyploid dogroses (Rosa sect. Caninae)

Molecular systematics, historical ecology, and phylogeography of Halimeda (Bryopsidales)

Plant hybridization

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