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Phylogeography of the longnose dace (Rhinichthys cataractae) species group in northwestern North America - the origin and evolution of the Umpqua and Millicoma dace

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The Umpqua and Millicoma dace are small cyprinid fishes endemic, respectively, to the Umpqua and Coos rivers on the central coast of Oregon. The origins and relationships of these dace are unclear; however, two hypotheses have been postulated that assume these dace had evolved from a longnose dace (Rhinichthys cataractae (Valenciennes, 1842)) like ancestor, but from different modes of origin. The direct origin hypothesis postulates that each of these dace originated directly, but independently, from a common ancestor. In contrast, the indirect origin hypothesis postulates that the Umpqua dace originated from a R. cataractae like ancestor and that the Millicoma dace evolved from the Umpqua dace. We used mitochondrial (cytochrome b and control region) sequences to test the two hypotheses. Our maximum likelihood analysis supports the indirect origin hypothesis and argues that together the Umpqua and Millicoma dace form a distinctive Oregon coastal clade within the R. cataractae species group. We also attempt to reconcile this result with the observation that the geographic distribution of the morphologically divergent Umpqua dace is sandwiched between the geographic ranges of the morphologically similar Millicoma dace and longnose dace.

Les naseux de l’Umpqua et de la Millicoma sont de petits poissons cyprinidés endémiques, respectivement dans les rivières Umpqua et Coos de la côte centrale de l’Oregon. L’origine et les relations de ces naseux sont incertaines; on a cependant élaboré deux hypothèses qui présupposent que ces naseux ont évolué à partir d’un ancêtre de type naseux des rapides (Rhinichthys cataractae (Valenciennes, 1842)), mais par des modes d’origine différents. L’hypothèse d’origine directe énonce que chacun de ces naseux tire son origine directement, mais indépendamment, d’un ancêtre commun. En revanche, l’hypothèse d’origine indirecte énonce que le naseux de l’Umpqua provient directement d’un ancêtre de type R. cataractae et que le naseux de la Millicoma a évolué à partir du naseux de l’Umpqua. Nous avons testé les deux hypothèses à l’aide de séquences mitochondriales (cytochrome b et région de contrôle). Une analyse de vraisemblance maximale appuie l’hypothèse d’origine indirecte et indique qu’ensemble les naseux de l’Umpqua et de la Millicoma forment un clade distinct de la côte d’Oregon au sein du groupe d’espèces de R. cataractae. Nous essayons aussi de réconcilier ce résultat avec l’observation que la répartition géographique des naseux de l’Umpqua, qui sont différents par leur morphologie, se trouve insérée entre les répartitions géographiques des naseux de la Millicoma et des naseux des rapides qui se ressemblent morphologiquement.

Document Type: Research Article

Publication date: June 1, 2009

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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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