The heterochromatin of grasshoppers from the Caledia captiva species complex

Arnold, Michael L.; Shaw, David D.

doi:10.1007/bf00293167

Chromosoma

1985

DOI: 10.1007/bf00293167

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The heterochromatin of grasshoppers from the Caledia captiva species complex

Michael L. Arnold

David D. Shaw

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1986

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Cited by 21 publications

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“…In particular, two subspecies (Moreton and Torresian) of C. captiva meet and form a zone of hybridization in southeast Queensland (4,5). These subspecies are differentiated at the level oftheir chromosome structure, the patterns of allozyme variation and by the distribution and abundance of highly repeated DNA sequences (6)(7)(8)(9). In laboratory hybridization experiments it has been demonstrated that the F2 generation is completely inviable, while the backcross generations show =50%o reduction in viability (10).…”

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Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper

Arnold

Shaw

Contreras

1987

Proc. Natl. Acad. Sci. U.S.A.

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A ribosomal RNA-encoding DNA (rDNA) cloned sequence, consisting of a 0.8-kilobase fragment from the 26S/nontranscribed spacer region, was used to identify diagnostic restriction enzyme fragments that distinguish the Moreton and Torresian subspecies of the grasshopper Caledia captiva. These restriction fragments were then used to study patterns of rDNA variation across a narrow geographical hybrid zone between the two subspecies. The pattern of rDNA variation that emerged after the analysis ofover 250 individuals clearly demonstrates the asymmetrical introgression of the Moreton ribosomal RNA genes into the Torresian subspecies. This asymmetric movement of genetic material occurs even though there exists extreme postmating F2 and backcross inviability between the two subspecies. From our data, as well as those of previous chromosomal and allozymic studies, we are able to support the occurrence of nonrandom processes such as biased gene conversion and/or natural selection. Because the rDNA loci in the Moreton and Torresian individuals are located in different regions on chromosomes 10 and 11, it should be possible to determine the relative contributions of conversion, natural selection, and these sorts of processes to the pattern of introgression of the Moreton rDNA into the Torresian subspecies.How reproductive isolation develops during the speciation process remains a fundamental and unanswered question in evolutionary biology. As a corollary ofthis question, one can inquire about the consequences of repeated hybridization between partially reproductively isolated populations. Grant (1) has stated, in reference to the findings of Anderson (2), that long-term backcrossing of hybrid individuals to the parental types can result in ".... convergences between previously separate phyletic lines ...." However, it is also apparent that the introduction, maintenance, and persistence of foreign genetic material, despite significant pre-and/or postmating isolation, must be mediated by factors such as genetic drift, migration, and/or natural selection. Thus, the definition of interacting processes that lead to introgression (2) of genetic material is of fundamental importance in understanding how genetic systems may be perturbed. Indeed, it has been advocated that a major stimulus to speciation involves hybridization (3). Furthermore, the quantitation of the effects of factors such as genetic drift, migration, and selection is equally fundamental in understanding the evolution of organisms.In order to examine the above parameters, it is necessary to identify hybridizing taxa that have the following characteristics: (i) significant levels of reproductive isolation; (ii) morphological, physiological, or genetic markers that can be used to identify genomic components in parental and hybrid individuals; and (iii) definable differences in the habitats occupied by the taxa. Such a system has been identified in the grasshopper Caledia captiva. In particular, two subspecies (Moreton and Torresian) of C. captiva meet and f...

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confidence: 99%

Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper

Arnold

Shaw

Contreras

1987

Proc. Natl. Acad. Sci. U.S.A.

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Interspecies comparison of the highly-repeated DNA of Australasian Luzula (Juncaceae)

Collet

Westerman

1987

Genetica

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The woodrush genus Luzula is characterised by having holocentric chromosomes. DNA of nine related Australasian species shows similar satellite DNAs which re very similar in nucleotide sequence content and unit length. Differences between the repetitive DNAs are evident as either the presence or absence of particular restriction enzyme sites. Sequence variants have probably been introduced into the repeated DNA components of ancestral species and particular variants reamplified during the evolution of the genus. Sequence amplification appears to be restricted to sequences already present in the genome rather than the de novo generation of repeats. The evolution of highly-repeated DNA sequences dispersed throughout the holocentric chromosomes of Luzula thus appears to be very similar to that known in eukaryotes with the more normal monocentric chromosome organisation.

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The effects of chromatin diminution on the pattern of C-banding in the chromosomes of Acanthocyclops vernalis Fischer (Copepoda: Crustacea)

Standiford

1989

Genetica

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Chromatin diminution is the loss of selected regions of pre-somatic cell chromosomes during early development, resulting in the removal of a large amount of the genomic DNA from the pre-somatic cells. In copepods, diminution is characterized by the formation of heterochromatically staining regions, or H-segments, which contain the chromatin to be lost. The removal of H-segments during diminution also must represent a major restructuring of the chromosomes which contained them. In order to examine the effects of diminution on the morphology and structure of the chromosomes, the C-banding technique was used. This procedure revealed that most C-bands present in the pre-diminution complement were absent in the post-diminution set. Additionally, in order to explore further the possible composition of the DNA contained in H-segments, a comparison, based on the relationship of C-bands to highly-repetitive DNA in chromosomes, was made between pre-diminution C-bands and H-segments. This comparison showed that not all H-segments are at chromosomal locations which produce a C-band, indicating that H-segments are perhaps not entirely composed of genetically inert DNA, as is currently supposed.

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The heterochromatin of grasshoppers from the Caledia captiva species complex

Cited by 21 publications

References 36 publications

Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper

Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper

Interspecies comparison of the highly-repeated DNA of Australasian Luzula (Juncaceae)

The effects of chromatin diminution on the pattern of C-banding in the chromosomes of Acanthocyclops vernalis Fischer (Copepoda: Crustacea)

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