Phenotypic diversity arising from a limited number of founders: A study of dental variation in laboratory colonies of collared lemmings, Dicrostonyx (Rodentia: Arvicolinae)

Abstract

The effects of close breeding upon dental phenotype are analysed in three laboratory colonies of Dicrostonyx using traditional comparative methods and a previously developed approach to quantify dental complexity in Arvicolinae. Across ten to 12 generations, dental complexity fluctuates within the range of variability inherited from the colony founders and shows no shifts towards complication. The finite number of founders (ten or fewer) favours the accumulation of rare dental traits inherited from the founders and leads to the appearance of atavisms and phenotypic outliers with extremely simple patterns of dentition. The atavistic patterns on m1, M1 and M3 revealed in two colonies of Dicrostonyx torquatus recapitulate the traits of the Miocene species Microtocricetus molassicus, which has been regarded previously as an evolutionary dead end in Cricetidae. A comparison with other arvicoline lineages suggests that one of the atavisms shared by D. torquatus and Microtocricetus could also be found in Microtus and Lemmus as an extremely rare trait, thus raising a question regarding the close relatedness of Microtocricetus to the present-day Arvicolinae. A perspective on the practical application of rare dental traits to detect close-breeding events in natural populations, living and extinct, is considered and exemplified for a particular case of arvicoline rodents.