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Mammalian Biology

, Volume 71, Issue 5, pp 288–298 | Cite as

Geometric morphometric analysis of geographic variation in the Río Negro tuco-tuco, Ctenomys rionegrensis (Rodentia: Ctenomyidae)

  • Alejandro D’Anatro
  • Enrique P. LessaEmail author
Original investigation

Abstract

A fundamental issue in the study of intraspecific variation is the analysis of how it is allocated within and between local populations. The genus Ctenomys represents an excellent model for studying such kinds of phenomena, and Ctenomys ríonegrensis is particularly interesting for the study of the processes driving geographic differentiation. This species occupies a relatively small area in Uruguay, where it is restricted to sand dunes. Throughout its distribution, these “tuco-tucos” show conspicuous phenotypic variation in the form of three easily distinguishable pelage colours: melanic, agouti and dark-backed. These observations contrast with the usual correlation between pelage and substrate colour found among small mammals, including other tuco-tucos and subterranean rodents on other continents. Different hypotheses have been advanced to explain the population structure pattern found in this tuco-tuco, including the random fixation of alternative pelage colours by drift and the possible role of an unknown type of selection to compensate possible predation pressures against melanic individuals. We analyse the geographic variation in the cranial shape of C. rionegrensis along its distribution range, using geometric morphometric techniques. Thirteen landmarks, assumed to be homologous among all specimens analysed, were chosen in each of three views of the skull. The discriminant function analyses performed over the partial warps and uniform components scores matrix do not discriminate among different pelage types regardless of the view of the skull considered. In contrast, the discriminant function showed a better separation among local populations. No correlation was found between geographic and morphological distances, or between genetic and morphological distances, among pairs of popualtions studied. This geometric morphometric approach had proved to be sensitive enough to detect a similar pattern of population structure that the molecular markers employed before.

Key words

Ctenomys rionegrensis geographic variation geometric morphometrics 

Geometrisch morphometrische Analyse geografischer Variationen des Río Negro Tuco-Tuco Ctenomys rionegrensis (Rodentia: Ctenomyidae)

Zusammenfassung

Eine fundamentale Angelegenheit beim Studium intraspezifischer Variationen, ist die Analyse ihrer Zuordnung innerhalb und zwischen lokalen Populationen. Die Gattung Ctenomys repräsentiert hierbei ein exzellentes Modell für solche Phänomene und insbesondere Ctenomys rionegrensis ist dabei interessant, um Prozesse zu studieren, die geografische Differenzierungen hervorrufen. Diese Spezies bewohnt ein relativ kleines Gebiet in Uruguay, das sich auf Sanddünen beschränkt. Im Verlaufe ihrer Verbreitung, zeigen diese “Tuco-Tucos“ auffallend phänotypische Variationen in Form von drei einfach zu unterscheidenden Farben des Haarkleids: melanistisch, agouti und mit schwarzem Rücken. Diese Beobachtungen stehen im Gegensatz zu den gewöhnlichen Korrelationen zwischen Haarkleid und -farben die bei kleinen Säugern gefunden wurden, einschließlich anderer tuco-tucos und unterirdisch lebender Nagetiere anderer Kontinente. Verschiedene Hypothesen wurden weiterentwickelt, um das Populationsstrukturmodell zu erklären, welches bei diesen Tuco-Tucos gefunden wurde, einschließlich der zufälligen Manifestierungen alternativer Farben des Felles und der möglichen Rolle eines unbekannten Typs Selektion, der einen mögliche Gefährdung durch Fressfeinde gegen melanistische Individuen ausgleicht. Wir analysieren die geografische Variation der Schädelform von C. rionegrensis in seinem Verbreitungsgebiet, indem wir geometrisch morphometrische Techniken verwenden. Dreizehn Markierungspunkte, die als homolog unter allen untersuchten Individuen, die analysiert wurden angesehen werden, wurden in jeder der drei Ansichten des Schädels ausgewählt. Die Diskriminanzfunktionsanalyse, die mit den einzelnen Ketten und Auswertungsmatrizen von Einheitskomponenten ausgeführt wurde, unterscheidet sich nicht bei den verschiedenen Typen von Fellfarben ungeachtet der Ansicht des jeweiligen Schädels. Demgegenüber zeigte die Diskriminanzfunktion eine bessere Abgrenzung bei lokalen Populationen. Es wurde kein Zusammenhang zwischen geografischen und morphologischen Unterschieden oder genetischen Abweichungen gefunden, von denen in einer früheren Arbeit und in der zuletzt zitierten berichtet wurde. Dieser geometrisch morphologische Ansatz ist nachweislich sensibel genug, ein Modell der Populationsstruktur zu ermitteln, das die Molekular-Kennzeichnungen schon vorher anwandten.

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Copyright information

© Deutsche Gesellschaft für Säugetierkunde 2006

Authors and Affiliations

  1. 1.Sección Evolución y SistemáticaFacultad de CienciasMontevideoUruguay

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