Genome size variation and evolution in North American cyprinid fishes

Abstract

Genome sizes (nuclear DNA contents) were documented spectrophotometrically for 29 species of North American cyprinid fishes. The data were then merged with comparable genome size data (published previously) from an additional 20 North American cyprinid species. The distributions of DNA values within populations of the 49 cyprinid species were essentially continuous and normal. The proportion of DNA which apparently is free to vary quantitatively within cyprinid populations appears to be between 4 and 5 % of the genome. The distribution of DNA values among cyprinid species was more-or-less continuous, with considerable overlap among species with intermediate DNA values. Analysis of the average genome size difference (distance) between individuals drawn from successive levels of evolutionary divergence indicated that: (i) the majority of genome size divergence in North American c prinids has occurred above the level of individuals within populations of species, and (ii) the degree of genome size divergence in the extremely speciose cyprinid genus Notropis is greater than that between species in other, less speciose cyprinid genera. The hypothesis that genome size change might be concentrated in speciation episodes was tested by comparing the means and variances of genome size difference (distance) between species in the cyprinid genus Notropis (a species-rich phylad) and the centrarchid (sunfish) genus Lepomis (a species-poor phylad). The ratios of mean distances and variances in the Notropis versus Lepomis comparisons were greater than unity, suggesting that changes in genome size in cyprinids may be correlated with speciation episodes. Whether or not genome size change in cyprinids occurs at speciation sensu strictu is problematic. The data suggest that separate facets or levels of the cyprinid genome may follow independent evolutionary paths. genome size (DNA content) / cyprinid fish / natural selection / speciation Résumé -Variation et évolution de la taille du génome chez les cyprinidés d'Amérique du Nord -La taille du génome (estimée par la quantité d'ADN nucléaire) de 29 espèces Nord-Américaines de cyprinidés a été mesurée par spectrophométrie; les résultats ont ensuite été jumelés à des données comparables publiées antérieurement, obtenues sur 20 autres espèces de cyprinidés de la même aire géographique, et les analyses ont été conduites sur l'ensemble de ces données. Au sein des populations, la quantité d'ADN nucléaire suit une distribution continue et normale, et varie dans une proportion qui représente 4 à 5% du génome. Etudiée sur l'ensemble des espèces, la quantité d'ADN nucléaire présente une distribution quasiment continue, avec des chevauchements considérables entre espèces. * Correspondence and reprints L'analyse de la variation observée parmi des individus tirés dans des niveaux taxonomiques variés indique que: -la variation est essentiellement due aux variations entre espèces et non aux variations entre individus d'une même espèces, et que, -la variation entre espèces est plus étendue dans le gen...

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Evolution of Genome Size in Drosophila. Is the Invader's Genome Being Invaded by Transposable Elements?

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