Chromosome differentiation, hybrid breakdown and the maintenance of a narrow hybrid zone in Caledia

Shaw, David D.; Wilkinson, Pat

doi:10.1007/bf00327563

Cited by 56 publications

(34 citation statements)

References 49 publications

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“…Similar results were found in a study of chiasma distribution along bivalent 1 of two chromosomally differentiated taxa of the grasshopper Caledia captiva (Shaw & Wilkinson, 1980). These taxa were supposed to differ by a pericentric inversion in chromosome 1, transforming an acrocentric chromosome of 'Torresian' variety into a metacentric chromosome of 'Moreton' variety.…”

Section: Discussionsupporting

confidence: 82%

Positional control of chiasma distribution in the house mouse. Chiasma distribution in mice homozygous and heterozygous for an inversion in chromosome 1

et al. 1991

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An examination of the chiasma distribution in chromosome 1 of male mice homozygous and heterozygous for a distal inversion In( 1) 1 2Rkand in normal males was carried out. No differences in chiasma distribution were found between homozygotes for the inversion and homozygotes for normal chromosome 1. A significant decrease in the frequency of bivalents bearing chiasmata in the pretelomeric region was found in heterozygotes. This, in its turn, produced a redistribution of chiasmata in the proximal non-inverted part of bivalent 1. These results could be interpreted as evidence for positional control of the chiasma distribution pattern: the distance of certain parts of the chromosome from the telomere and chiasmata interference are more important for determination of the chiasma frequency in a given region than its genetic content.

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Section: Discussionsupporting

confidence: 82%

Positional control of chiasma distribution in the house mouse. Chiasma distribution in mice homozygous and heterozygous for an inversion in chromosome 1

et al. 1991

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“…Queensland. Although the zone has been studied in some detail by Moran (1979), and hybrid breakdown among the F2 and backcross generations can adequately explain its structure (Shaw and Wilkinson, 1980), no evidence was found in either of these studies to indicate any functional significance for the karyotypic repatterning which distinguish the taxa. Subsequent laboratory analyses by Coates and Shaw (1982) and Shaw et a!., (1982) revealed that all of the hybrid breakdown was attributable to intra chromosomal effects caused by major changes to the recombination system in F1 hybrids.…”

Section: Introductionmentioning

confidence: 96%

“…(c) The most significant feature of these two chromosomally distinct taxa is that they are only partially reproductively isolated (Shaw and Wilkinson, 1980) and form an extremely narrow zone of hybridisation in S.E. Queensland.…”

Section: Introductionmentioning

confidence: 99%

Temporal variation in the chromosomal structure of a hybrid zone and its relationship to karyotypic repatterning

et al. 1985

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A temporal analysis of the chromosomal structure of the hybrid zone in the grasshopper Caledia captive has revealed that, over a period of six generations, the position of the zone has remained unchanged when assessed in terms of chromosomal frequencies. In complete contrast however, chromosomal genotypic frequencies have changed dramatically and asymmetrically over the same period. The frequencies of chromosomal heterozygotes have been significantly reduced on one side of the zone accompanied by increases in the frequencies of homozygous metacentric chromosomes. These asymmetrical genotypic changes are also reflected in a complete reversal of the patterns of gametic disequilibria (Tr2) across the zone. It is proposed that undirectional selection has favoured a metacentric karyotype on one side of the zone during a major climatic change.The structure of the hybrid zone involves two major and independent features. First, as a secondary consequence of hybridisation, recombinational change in F1 hybrids disrupts the internal organisation within chromosomes. This results in the production of inviable F2 and backcross progeny and hence, explains the structure of the zone in terms of the sharp change in chromosomal frequencies. Secondly, the asymmetrical nature of the gametic disequilibria between chromosomes represents the direction of selection which favours an acrocentric Torresian karyotype in dry years and a metacentric Moreton karyotype during mesic years. Variation in both chromosome structure and embryonic weight is associated with the predictability of the environment. The acrocentric Torresian karyotype and its associated larger embryos are correlated with a univoltine life history in drier, unpredictable habitats. A similar pattern exists within the Moreton subspecies in the form of a chromosomal dine in S.E. Australia. At the southern limit of this dine the karyotype is totally acrocentric, the life history is univoltine and the embryos are the same weight as the Torresian.It is speculated that variation in chromosomal structure, in terms of the relationship between centromeres and telomeres, may provide a mechanism for altering cellular phenotype through changes in such factors as replication patterns or chromatin packaging which may act quite independently of the informational content of the chromosome.

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“…The taxonomic species Caledia captiva has undergone extensive chromosomal divergence resulting in at least four distinct chromosomal taxa which show various levels of inter taxon reproductive isolation (Daly et aL, 1981;Shaw and Wilkinson 1980). There are now many examples of speciation events which are associated with chromosome repatterning and a number of hypotheses have been presented to provide a causal role for chromosomal 85 re-arrangements in speciation (see Grant 1971;White 1978;Bush 1981;Charlesworth et aL, 1982).…”

Section: Introductionmentioning

confidence: 99%

“…This evidence was derived primarily from hybridisation studies which demonstrated that even though F3 hybrids were fully viable and fertile, the F2 and backcross generations showed a reduction in viability of 100 per cent and 50 per cent respectively. Furthermore, meiosis in the F3 hybrids generally showed normal bivalent formation (Moran 1980;Shaw and Wilkinson 1980; Coates and Shaw 1982) even though the two taxa are differentiated by at least seven pericentric rearrangements and a complex pattern of heterochromatic bands. The only noticeable effect of chromosomal heterozygosity upon meiosis was the redistribution of chiasmata.…”

Section: Introductionmentioning

confidence: 99%

The chromosomal component of reproductive isolation in the grasshopper caledia captiva III. Chiasma distribution patterns in a new chromosomal taxon

Coates

Shaw

1984

Heredity

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SUMMARYAn analysis of chiasma distribution patterns among two classes of F1 hybrids produced by crossing a new chromosomal taxon, Lakes Entrance (LE), to both the Moreton (MAX) and Torresian (TT) taxa, has demonstrated that, when compared to their parental taxa, the (MAX < LE)F hybrids have very different distribution patterns whereas the (LE XTT)F1 hybrids have similar distribution patterns. Chiasmata in the Lakes Entrance and Torresian taxa, and their F1 hybrids generally show proximal-distal patterns of localisation in five of the eight largest autosomes although some subtle statistical differences were detected between the F1 hybrids and the parental taxa in those chromosomes. The highly significant differences in chiasma distribution patterns between the (MAX X LE)FI hybrids and their parental taxa in chromosomes 1, 2, 4, 5, 6 and 8 can be directly attributed to pericentric heterozygosity. In these cases most recombination is localised in the interstitial and distal regions of the chromosomes. Although pericentric heterozygosity would be expected to result in a reduced mean cell chiasma frequency, the (MAX x LE)FI hybrids have the same mean cell chiasma frequency as both the MAX and TI' taxa and the (LE XTT)FIhybrids. This appears to be due to the presence of exchanges (scored as chiasmata) within the pericentric re-arrangement region. The data strongly suggest that these exchanges are U-type following straight non-homologous pairing at pachytene rather than the result of crossing over following homologous pairing within an inversion loop. In gross stained meiotic material U-type exchanges were in 15-5 per cent of cells scored. The analysis of chiasma distribution in the F1 hybrids from crosses between the chromosomally divergent but genically equivalent MAX and LE taxa provides further substantive evidence that the dramatic change in the pattern.of recombination in chromosomally heterozygous F1's disrupts intrachromosomal organisation resulting in the generation of recombinant progeny incapable of completing embryogenesis. In comparison the lack of any noticeable change in the recombination system in the F1 hybrids from crosses between the genically divergent but chromosomally similar taxa, LE and IT, suggests that the F2 inviability in this case is most likely a consequence of recombination between genically divergent genomes involving whole chromosome segregation rather than extensive intrachromosomal recombination.

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Chromosome differentiation, hybrid breakdown and the maintenance of a narrow hybrid zone in Caledia

Cited by 56 publications

References 49 publications

Positional control of chiasma distribution in the house mouse. Chiasma distribution in mice homozygous and heterozygous for an inversion in chromosome 1

Positional control of chiasma distribution in the house mouse. Chiasma distribution in mice homozygous and heterozygous for an inversion in chromosome 1

Temporal variation in the chromosomal structure of a hybrid zone and its relationship to karyotypic repatterning

The chromosomal component of reproductive isolation in the grasshopper caledia captiva III. Chiasma distribution patterns in a new chromosomal taxon

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