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Chiasmate meiosis in male black fly (Diptera: Simuliidae) larvae associated with mermithid infections (Nematoda: Mermithidae)

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Mermithid nematodes (Nematoda: Mermithidae) parasitize larval, pupal, and adult black flies (Diptera: Simuliidae) and may result in the development of intersex adults, generally considered to be feminized males. Simuliid gonad morphology and meiotic chromosome condition were examined in both early-instar larvae and late-instar larvae (≍ pharate pupae) to determine the developmental stage at which mermithid-associated feminization was initiated. We found that feminization occurred in early-instar larvae prior to gill histoblast formation. Infected larvae were morphologically male (rounded testes present) or female (elongated ovaries present), with morphological males exhibiting either male (achiasmate) or female (chiasmate) meiotic chromosomes; morphological females only had chiasmate chromosomes. Mermithid infection can also inhibit simuliid gonad development completely.

Les nématodes mermithidés (Nematoda : Mermithidae) parasitent les larves, les nymphes et les adultes des mouches noires (Diptera : Simuliidae) et peuvent causer l’apparition d’adultes intersexués, généralement considérés comme des mâles féminisés. Nous avons examiné la morphologie des gonades et la condition des chromosomes en méiose à la fois chez des larves jeunes et des larves de stades avancés (≍ nymphes avec adultes inclus) de simulies afin de déterminer à quel moment débute la féminisation associée aux mermithidés. La féminisation se fait dans les premiers stades larvaires avant la formation des histoblastes des branchies. Les larves infectées ont une morphologie de mâle (présence de testicules ronds) ou de femelle (présence d’ovaires allongés); les mâles morphologiques possèdent des chromosomes en méiose ou bien mâles (sans chiasma) ou alors femelles (avec chiasmas); les femelles morphologiques n’ont que des chromosomes avec des chiasmas. Les infections à mermithidés peuvent aussi inhiber complètement le développement des gonades chez les simuliidés.

[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2008-10-01

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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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