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Inversion polymorphism in a Connecticut River Axarus species (Diptera: Chironomidae): biometric effects of a triple inversion heterozygote

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The authors sampled three spatially isolated populations of a chironomid midge in the genus Axarus living in the Connecticut River both early and late in the larval life cycle of one generation. Larvae were scored for both length and inversion frequency using the polytene chromosomes from salivary gland cells. We found polymorphism for four paracentric inversions. Inversion C1–6 exhibits a geographic cline, increasing in frequency with increasing latitude but remaining stable over time. Also stable over time were two other paracentric inversions designated A1–5 and F13–20, which were present at similar frequencies in all populations. None of these inversions was associated with larval length. A complex triple inversion designated G2–7 was significantly correlated with decreased larval length and also exhibited a significant increase in frequency (within one cohort) in the two more northerly populations. We propose that this increase is due to size-selective predation eliminating larger larvae.

Nous avons échantillonné trois populations isolées d'un chironomide du genre Axarus habitant le fleuve Connecticut, au début et à la fin de leur développement larvaire dans une même génération. Les larves ont été codées en fonction de leur longueur et de la fréquence d'inversions sur les chromosomes polytènes des cellules de leurs glandes salivaires. Il existe un polymorphisme impliquant quatre inversions paracentriques. L'inversion C1–6 suit un gradient géographique et sa fréquence augmente avec la latitude; elle reste cependant stable dans le temps. Deux autres inversions paracentriques, A1–5 et F13–20, sont aussi stables dans le temps et elles sont présentes dans toutes les populations à des fréquences semblables. Une inverse triple complexe, G2–7, est en corrélation négative significative avec la taille des larves; sa fréquence augmente aussi, dans une même cohorte, dans les deux populations situées plus au nord. Nous posons en hypothèse que cet accroissement est due à une prédation sélective en fonction de la taille qui élimine les plus grandes larves.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-01-01

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