Chromosomal Differentiation among the Annual Helianthus Species

Chandler, John; Jan, Chao‐Chien; Beard, Benjamin H.

doi:10.2307/2419126

Cited by 147 publications

(168 citation statements)

References 11 publications

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“…If fertility selection were the only important force determining genomic content, we might not expect the three hybrid species to be so distinct, differing in morphology, habitat preference, and karyotype (Chandler et al 1986). Presumably, genomic composition is also shaped by strong habitat-mediated selection, which contributes to modern species differences.…”

Section: Discussionmentioning

confidence: 99%

Reconstructing the Origin of Helianthus deserticola: Survival and Selection on the Desert Floor

Gross¹,

Kane²,

Lexer³

et al. 2004

The American Naturalist

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The diploid hybrid species Helianthus deserticola inhabits the desert floor, an extreme environment relative to its parental species Helianthus annuus and Helianthus petiolaris. Adaptation to the desert floor may have occurred via selection acting on transgressive, or extreme, traits in early hybrids between the parental species. We explored this possibility through a field experiment in the hybrid species' native habitat using H. deserticola, H. annuus, H. petiolaris, and two populations of early-generation (BC 2 ) hybrids between the parental species, which served as proxies for the ancestral genotype of the ancient hybrid species. Character expression was evaluated for each genotypic class. Helianthus deserticola was negatively transgressive for stem diameter, leaf area, and flowering date, and the latter two traits are likely to be advantageous in a desert environment. The BC 2 hybrids contained a range of variation that overlapped these transgressive trait means, and an analysis of phenotypic selection revealed that some of the selective pressures on leaf size and flowering date, but not stem diameter, would move the BC 2 population toward

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Section: Discussionmentioning

confidence: 99%

Reconstructing the Origin of Helianthus deserticola: Survival and Selection on the Desert Floor

Gross¹,

Kane²,

Lexer³

et al. 2004

The American Naturalist

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show abstract

“…The search for chromosomal markers in other species of the genus Helianthus is helpful in a taxon where (i) there are diploid, tetraploid and hexaploid species, all of which have a basic chromosome number of x = 17 and are probably of polyploid origin (Jackson & Murray, 1983;Chandler et a!., 1986); (ii) different races of the same Helianthus species may be chromosomally distinct, although successful crosses may be produced between perennial and annual species, and between diploid and polyploid species (Kulshreshtha & Gupta, 1979); (iii) the cytogenetical information comes almost exclusively from the analysis of interspecific hybrid meiotic configurations (Chandler, 1991). These chromosomal markers could be useful either from the taxonomic point of view to identify chromosomes from different genomes or to follow the introgression of alien chromosomes in cultivated sunflowers, as happens in other plant species (Gustafson & Dille, 1992;Werner et al, 1992).…”

Section: Discussionmentioning

confidence: 99%

“…Most of the karyological information about this taxon has come from the analysis of meiotic pairing in interspecific hybrids in the study of hybrid fertility, introgression and genome relationships (Chandler et al, 1986;Chandler, 1991).…”

Section: Introductionmentioning

confidence: 99%

Chromosomal differentiation in Helianthus annuus var. macrocarpus: heterochromatin characterization and rDNA location

et al. 1996

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The 2n = 34 chromosomes of the inbred line HA89, and the Flamme and Mirasol hybrids of Helianthus annuus var. macrocarpus possess centromeric heterochromatin as established by Giemsa C-banding. This heterochromatin can not be differentiated by fluorochromes such as DAPI or Chromomycin A3, with selective affinity for specific DNA base pairs. This situation probably results from either a balanced AT/GC composition of the involved repeat or the existence of alternating repetitive sequences of opposite base pair composition in these heterochromatic areas. However, there is also heterochromatin associated with the secondary constrictions on three pairs of chromosomes. This heterochromatin appears to be GC-rich according to its response to the fluorochrome treatments, thus indicating heterochromatin heterogeneity in H. annuus. Silver staining reveals the existence of active NORs associated with these secondary constrictions. In situ hybridization with an rDNA probe confirms these results and makes the existence of other inactive rDNA sites unlikely. These results are relevant to evolutionary and breeding studies on sunflowers.

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“…1) and molecular data are consistent with the absence of interspecific gene flow during their entire history of divergence 20 . These two species are nevertheless still capable of producing partially fertile hybrids in control crosses 21 .…”

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confidence: 99%

Genomic islands of divergence are not affected by geography of speciation in sunflowers

et al. 2013

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Genomic studies of speciation often report the presence of highly differentiated genomic regions interspersed within a milieu of weakly diverged loci. The formation of these speciation islands is generally attributed to reduced inter-population gene flow near loci under divergent selection, but few studies have critically evaluated this hypothesis. Here, we report on transcriptome scans among four recently diverged pairs of sunflower (Helianthus) species that vary in the geographical context of speciation. We find that genetic divergence is lower in sympatric and parapatric comparisons, consistent with a role for gene flow in eroding neutral differences. However, genomic islands of divergence are numerous and small in all comparisons, and contrary to expectations, island number and size are not significantly affected by levels of interspecific gene flow. Rather, island formation is strongly associated with reduced recombination rates. Overall, our results indicate that the functional architecture of genomes plays a larger role in shaping genomic divergence than does the geography of speciation.

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Chromosomal Differentiation among the Annual Helianthus Species

Cited by 147 publications

References 11 publications

Reconstructing the Origin of Helianthus deserticola: Survival and Selection on the Desert Floor

Reconstructing the Origin of Helianthus deserticola: Survival and Selection on the Desert Floor

Chromosomal differentiation in Helianthus annuus var. macrocarpus: heterochromatin characterization and rDNA location

Genomic islands of divergence are not affected by geography of speciation in sunflowers

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