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An intra- and inter-island study of the polytene chromosomes of Simulium exasperans (Diptera: Simuliidae)

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The polytene chromosome banding pattern of Simulium exasperans (Craig, 1987) is described for the first time. Three populations of S. exasperans from Moorea and Tahiti were examined cytologically. Interspecific comparisons revealed that S. exasperans is homosequential in chromosomal banding pattern to Simulium cataractarum (Craig, 1987), but contains three species-characteristic floating inversions: IL-1ex.2ex, IIL-1ex,2ex, and IIIL-1ex. No sex-linked inversions were identified; males and females had undifferentiated sex chromosomes. The IIL-1ex,2ex inversion was in Hardy-Weinberg disequilibrium in two of the three populations. From this preliminary data, two cytotypes may exist: cytotype A (Belvedre Cascade population) and cytotype B (1st Afareaitu Cascade and Jardin Public Vaipahi populations). Contrary to phylogenetic and biogeographic data, it is hypothesized that the Belvedre Cascade population (cytotype A) is ancestral to the populations containing cytotype B. Furthermore, a heterozygote advantage may exist in cytotype B.

Nous décrivons pour la première fois le pattern des bandes sur les chromosomes polytènes de Simulium exasperans (Craig, 1987). Nous avons examiné la cytologie de trois populations de S. exasperans de Mooréa et de Tahiti. Des comparaisons interspécifiques indiquent que les chromosomes de S. exasperans possèdent la même séquence de bandes que Simulium cataractarum (Craig, 1987), mais avec trois inversions flottantes spécifiques, IL-1ex.2ex, IIL-1ex,2ex et IIIL-1ex. Il n'y a pas d'inversion liée au sexe; les mâles et les femelles ont des chromosomes sexuels non différenciés. L'inversion IIL-1ex,2ex est en déséquilibre Hardy-Weinberg dans deux des trois populations. D'après ces données préliminaires, il peut exister deux cytotypes, le cytotype A (population de la cascade du Belvédère) et le cytotype B (populations de la première cascade Afareaitu et du jardin public Vaipahi). Contrairement aux données phylogénétiques et biogéographiques, nous posons en hypothèse que la population de la cascade du Belvédère (cytotype A) est ancestrale aux populations qui contiennent le cytotype B. De plus, il peut exister de l'hétérosis chez le cytotype B.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-05-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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