Oolon Colluphid
01 Apr 2009, 12:14 PM
PNAS vol. 106 no. 13 pp. 5241-5245 (31 March 2009)
Recent speciation associated with the evolution of selfing in Capsella
Foxe et al.
The evolution from outcrossing to predominant self-fertilization represents one of the most common transitions in flowering plant evolution.
This shift in mating system is almost universally associated with the “selfing syndrome,” characterized by marked reduction in flower size and a breakdown of the morphological and genetic mechanisms that prevent self-fertilization.
In general, the timescale in which these transitions occur, and the evolutionary dynamics associated with the evolution of the selfing syndrome are poorly known.
We investigated the origin and evolution of selfing in the annual plant Capsella rubella from its self-incompatible, outcrossing progenitor Capsella grandiflora by characterizing multilocus [in many places] patterns of DNA sequence variation at nuclear genes.
We estimate that the transition to selfing and subsequent geographic expansion have taken place during the past 20,000 years. This transition was probably associated with a shift from stable equilibrium toward a near-complete population bottleneck causing a major reduction in effective population size.
The timing and severe founder event [loss of genetic variety due to the bottleneck] support the hypothesis that selfing was favored during colonization as new habitats emerged after the last glaciation and the expansion of agriculture.
[B]These results suggest that natural selection for reproductive assurance can lead to major morphological evolution and speciation on relatively short evolutionary timescales.
Same issue, pp. 5246-5251
Recent speciation of Capsella rubella from Capsella grandiflora, associated with loss of self-incompatibility and an extreme bottleneck
Guo et al.
Flowering plants often prevent selfing through mechanisms of self-incompatibility (S.I.). The loss of S.I. has occurred many times independently, because it provides short-term advantages in situations where pollinators or mates are rare.
The genus Capsella, which is closely related to Arabidopsis, contains a pair of closely related diploid [having pairs of chromosomes] species, the self-incompatible Capsella grandiflora and the self-compatible Capsella rubella.
To elucidate the transition to selfing and its relationship to speciation of C. rubella, we have made use of comparative sequence information. Our analyses indicate that C. rubella separated from C. grandiflora recently (≈30,000–50,000 years ago) and that breakdown of S.I. occurred at approximately the same time.
Contrasting the nucleotide [bits of DNA] diversity patterns of the 2 species, we found that C. rubella has only 1 or 2 alleles [varieties of gene] at most loci (http://en.wikipedia.org/wiki/Locus_(genetics)) [points on a chromosome], suggesting that it originated through an extreme population bottleneck.
Our data are consistent with diploid speciation by a single, selfing individual, most likely living in Greece. The new species subsequently colonized the Mediterranean by Northern and Southern routes, at a time that also saw the spread of agriculture. The presence of phenotypic diversity within modern C. rubella suggests that this species will be an interesting model to understand divergence and adaptation, starting from very limited standing genetic variation.
The second one is an Open Access article (http://www.pnas.org/content/106/13/5246.full).
Recent speciation associated with the evolution of selfing in Capsella
Foxe et al.
The evolution from outcrossing to predominant self-fertilization represents one of the most common transitions in flowering plant evolution.
This shift in mating system is almost universally associated with the “selfing syndrome,” characterized by marked reduction in flower size and a breakdown of the morphological and genetic mechanisms that prevent self-fertilization.
In general, the timescale in which these transitions occur, and the evolutionary dynamics associated with the evolution of the selfing syndrome are poorly known.
We investigated the origin and evolution of selfing in the annual plant Capsella rubella from its self-incompatible, outcrossing progenitor Capsella grandiflora by characterizing multilocus [in many places] patterns of DNA sequence variation at nuclear genes.
We estimate that the transition to selfing and subsequent geographic expansion have taken place during the past 20,000 years. This transition was probably associated with a shift from stable equilibrium toward a near-complete population bottleneck causing a major reduction in effective population size.
The timing and severe founder event [loss of genetic variety due to the bottleneck] support the hypothesis that selfing was favored during colonization as new habitats emerged after the last glaciation and the expansion of agriculture.
[B]These results suggest that natural selection for reproductive assurance can lead to major morphological evolution and speciation on relatively short evolutionary timescales.
Same issue, pp. 5246-5251
Recent speciation of Capsella rubella from Capsella grandiflora, associated with loss of self-incompatibility and an extreme bottleneck
Guo et al.
Flowering plants often prevent selfing through mechanisms of self-incompatibility (S.I.). The loss of S.I. has occurred many times independently, because it provides short-term advantages in situations where pollinators or mates are rare.
The genus Capsella, which is closely related to Arabidopsis, contains a pair of closely related diploid [having pairs of chromosomes] species, the self-incompatible Capsella grandiflora and the self-compatible Capsella rubella.
To elucidate the transition to selfing and its relationship to speciation of C. rubella, we have made use of comparative sequence information. Our analyses indicate that C. rubella separated from C. grandiflora recently (≈30,000–50,000 years ago) and that breakdown of S.I. occurred at approximately the same time.
Contrasting the nucleotide [bits of DNA] diversity patterns of the 2 species, we found that C. rubella has only 1 or 2 alleles [varieties of gene] at most loci (http://en.wikipedia.org/wiki/Locus_(genetics)) [points on a chromosome], suggesting that it originated through an extreme population bottleneck.
Our data are consistent with diploid speciation by a single, selfing individual, most likely living in Greece. The new species subsequently colonized the Mediterranean by Northern and Southern routes, at a time that also saw the spread of agriculture. The presence of phenotypic diversity within modern C. rubella suggests that this species will be an interesting model to understand divergence and adaptation, starting from very limited standing genetic variation.
The second one is an Open Access article (http://www.pnas.org/content/106/13/5246.full).