Nuclear and chloroplast microsatellites reveal extreme population differentiation and limited gene flow in the Aegean endemic <i>Brassica cretica </i>(Brassicaceae)

Edh, Kristina; Widén, Björn; Ceplitis, Alf

doi:10.1111/j.1365-294x.2007.03585.x

Cited by 49 publications

(59 citation statements)

References 86 publications

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“…A second finding consistent with theoretical prediction concerns population differentiation at the S locus in B. cretica, which, with F ST ¼ 0.145 for SRK and F ST ¼ 0.075 for SCR class II, is strikingly low compared to the extraordinary degree of population differentiation observed at neutral loci in this species (F ST ¼ 0.600 and 0.617 for allozymes and microsatellites, respectively, calculated among the populations included in this study from Widén et al 2002 andEdh et al 2007). Similar results were obtained by Glémin et al (2005) who found a lower population structure at the S locus than at microsatellite loci and a relatively high number of private haplotypes among Corsican populations of the wild B. insularis and by Kamau et al (2007) and Ruggiero et al (2008) who detected a significant decrease in F ST at markers close to the S locus in A. lyrata and A. halleri, respectively.…”

Section: Discussionsupporting

confidence: 65%

“…B. cretica is found in the eastern Mediterranean region, mainly on Crete and the surrounding Aegean islands, where it grows in isolated populations in cliff systems and ravines (Snogerup et al 1990). Populations on Crete show a high degree of genetic differentiation for a wide range of morphological and molecular characters (Widén et al 2002;Edh et al 2007), indicating a long history of genetic drift and low levels of gene flow among populations. B. cretica is self-incompatible, but individuals capable of setting seed after enforced self-pollination have been found in some of the studied populations (Rao et al 2002a,b).…”

Section: Methodsmentioning

confidence: 99%

“…First, Tajima's D statistic (Tajima 1989), which measures the deviation of the mutation frequency spectrum from a standard neutral model, was calculated for the total sample. As the samples originate from genetically differentiated subpopulations, the statistical significance of the hypothesis that D ¼ 0 was evaluated by comparing the observed value to a null distribution of D derived from 1000 coalescence simulations of an island model using u ¼ 4Nm estimated from the proportion of segregating sites (Watterson 1975) in the data and a migration rate of N m ¼ 0.315 (calculated from nuclear microsatellite data; Edh et al 2007). Simulations were performed in the ms computer program (Hudson 2002).…”

Section: Methodsmentioning

confidence: 99%

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Molecular Population Genetics of theSRKandSCRSelf-Incompatibility Genes in the Wild Plant SpeciesBrassica cretica(Brassicaceae)

2009

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Self-incompatibility (SI) in plants is a classic example of a trait evolving under strong frequency-dependent selection. As a consequence, population genetic theory predicts that the S locus, which controls SI, should maintain numerous alleles, display a high level of nucleotide diversity, and, in structured populations, show a lower level of among-population differentiation compared to neutral loci. Population-level investigations of DNA sequence variation at the S locus have recently been carried out in the genus Arabidopsis, largely confirming results from theoretical models of S-locus evolutionary dynamics, but no comparable studies have been done in wild Brassica species. In this study, we sequenced parts of the S-locus genes SRK and SCR, two tightly linked genes that are directly involved in the determination of SI specificity in samples from four natural populations of the wild species Brassica cretica. The amount and distribution of nucleotide diversity, as well as the frequency spectrum of putative functional haplotypes, observed at the S locus in B. cretica fit very well with expectations from theoretical models, providing strong evidence for frequency-dependent selection acting on the S locus in a wild Brassica species.

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Section: Discussionsupporting

confidence: 65%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Molecular Population Genetics of theSRKandSCRSelf-Incompatibility Genes in the Wild Plant SpeciesBrassica cretica(Brassicaceae)

2009

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“…Several closely related pairs of B. cretica/B. oleracea SRK haplotypes may represent additional examples of such interspecific pairs, a finding that would be expected, given that the divergence between B. cretica and B. oleracea dates back ,1 million years (Edh et al 2007), compared to nearly 4 million years for the B. oleracea-B. rapa divergence (Inaba and Nishio 2002).…”

Section: Discussionmentioning

confidence: 91%

“…B. cretica is found in the Aegean region, mainly on the island of Crete, where it grows in isolated populations in ravines and gorges (Snogerup et al 1990). As a result of severely restricted gene flow, Cretan populations of B. cretica show an exceptionally high level of neutral genetic differentiation both at molecular marker loci and for quantitative traits (Widén et al 2002;Edh et al 2007).…”

Section: Methodsmentioning

confidence: 99%

The Evolution and Diversification ofS-Locus Haplotypes in the Brassicaceae Family

2009

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Self-incompatibility (SI) in the Brassicaceae plant family is controlled by the SRK and SCR genes situated at the S locus. A large number of S haplotypes have been identified, mainly in cultivated species of the Brassica and Raphanus genera, but recently also in wild Arabidopsis species. Here, we used DNA sequences from the SRK and SCR genes of the wild Brassica species Brassica cretica, together with publicly available sequence data from other Brassicaceae species, to investigate the evolutionary relationships among S haplotypes in the Brassicaceae family. The results reveal that wild and cultivated Brassica species have similar levels of SRK diversity, indicating that domestication has had but a minor effect on S-locus diversity in Brassica. Our results also show that a common set of S haplotypes was present in the ancestor of the Brassica and Arabidopsis genera, that only a small number of haplotypes survived in the Brassica lineage after its separation from Arabidopsis, and that diversification within the two Brassica dominance classes occurred after the split between the two lineages. We also found indications that recombination may have occurred between the kinase domain of SRK and the SCR gene in Brassica.T O avoid self-fertilization, different kinds of selfincompatibility (SI) mechanisms have evolved in many plant families (Richards 1997). In most cases, SI is controlled by a single locus, the S locus, which, even though it often contains several genes, is inherited as a single Mendelian locus (Silva and Goring 2001); for this reason, S alleles are often referred to as S haplotypes (Boyes and Nasrallah 1993). In the Brassicaceae, which has the sporophytic type of SI where the pollen SI phenotype is determined by the S-locus genotype of the diploid parent, two S-locus genes, SRK and SCR, encode the maternal (pistil) and paternal (pollen) specificities, respectively (Stein et al. 1991;Schopfer et al. 1999;Suzuki et al. 1999). The SRK receptor consists of three domains with different functions: an extracellular S domain (encoded by exon 1 in SRK), which is the center for recognition of SCR; a transmembrane domain (exon 2) that passes through the plasma membrane; and an intracellular kinase domain (exons 4-7), which initiates the signaling cascade in the stigma cells (see Takayama and Isogai 2005). The SCR gene product is a small soluble protein molecule present at the pollen surface where it interacts with the S domain of its cognate SRK protein (Takayama et al. 2001). Because of the strong frequency-dependent selection acting on the SI system, the S locus typically maintains a large number of haplotypes (Lawrence 2000), and levels of diversity at both synonymous and nonsynonymous sites are high in the S domain of SRK and in SCR (e.g., Awadalla and Charlesworth 1999;Charlesworth et al. 2003;Takuno et al. 2007). Furthermore, in both Brassica and Arabidopsis, synonymous diversity is elevated in a region encompassing several tens of kilobases beyond the actual targets of selection due to the low level...

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Molecular phylogeography of Thymus herba-barona (Lamiaceae): Insight into the evolutionary history of the flora of the western Mediterranean islands

Molins

Bacchetta

Rosato

et al. 2011

TAXON

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Thymus herba‐barona is endemic to Majorca, Corsica, and Sardinia. In order to gain insight into its evolutionary history, we examined the genetic diversity and phylogeography of the species using sequences of the trnT‐trnL intergenic spacer from 106 individuals belonging to 15 populations. We detected high within‐species genetic diversity and strong among‐population differentiation, but no evidence for phylogeographic structure. A haplotype network supported the occurrence of three main clades, the ancestral one being geographically restricted to the Gennargentu massif in Sardinia, while the two derived ones were relatively widespread. Coalescent‐based analyses indicated deep divergence times and limited ongoing gene flow between major clades. The inferred evolutionary history of the species involved an early range expansion followed by successive fragmentation episodes, probably related to progressive climatic aridification since the Pliocene (3.2 Ma). Our data suggest that long‐distance dispersal events played a minor role in the evolutionary history of the species. The exact origin of the species remains unclear. The highly structured pattern of genetic variability detected suggests that random genetic drift played a major role in structuring genetic variation in this endemic plant. The cytogenetic evidence does not support the proposed recognition of three taxonomic entities within T. herba‐barona based on morphological discontinuities associated with different ploidy levels.

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Nuclear and chloroplast microsatellites reveal extreme population differentiation and limited gene flow in the Aegean endemic Brassica cretica (Brassicaceae)

Cited by 49 publications

References 86 publications

Molecular Population Genetics of theSRKandSCRSelf-Incompatibility Genes in the Wild Plant SpeciesBrassica cretica(Brassicaceae)

Molecular Population Genetics of theSRKandSCRSelf-Incompatibility Genes in the Wild Plant SpeciesBrassica cretica(Brassicaceae)

The Evolution and Diversification ofS-Locus Haplotypes in the Brassicaceae Family

Molecular phylogeography of Thymus herba-barona (Lamiaceae): Insight into the evolutionary history of the flora of the western Mediterranean islands

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