Comparative odontometrical analysis of the first lower molar in Microtus [Terricola] multiplex [Arvicolinae, Rodentia] from western Alps

The morphology of the first lower molar (M1) of Microtus (Terricola) multiplex (Fatio, 1905) was compared amongst 15 populations from the Alps (Switzerland, Italy, France). M. multiplex orientalis from Trentino Alto Adige is close to the nominative subspecies M. multiplex multiplex from Ticino characterised by a great size, a not tilted pitymyan rhombus and an important development of the anterior part of the M1. M. multiplex druentius from Ubaye mainly differs from the nominative subspecies by a smaller tooth size. Populations from Valle d’Aosta and Piemonte show on the whole a morphology intermediate between M. m. multiplex and M. m. druentius subspecies, however, the pitymyan rhombus is more tilted and the development of the anterior part more reduced in populations from Eastern and Central Piemonte. The Western populations (from Trièvès, Vercors, Royans and Chambaran) belonging to the subspecies M. m. niethammeri are the most differentiated with a small or median size of the M1, a reduced development of the anterior part and a very tilted pitymyan rhombus, particularly in the population from Chambaran. The populations from Matheysine and Grésivaudan are morphologically a link between M. m. druentius and M. m. niethammeri subspecies.