Summary: Airoldi, J.-P. & Hoffmann, R.S. (1984). Age variation in voles (Microtus californicus and M.
ochrogaster) and its significance for systematic studies. Occas. Pap. Mus. Nat. Hist. Univ.
Kansas 111 : 1-45.
A morphometric analysis of 314 specimens of Microtus californicus and 164 of M. ochrogaster
reared in the laboratory was conducted using 47 skull measurements, cranial and mandibular
weights and head+body length. Repeated measurements performed on a separate sample of M.
ochrogaster (n=10) were used to estimate the measuring error through a 2-way analysis of
variance. Nearly all variables can be considered as reliable when defined correctly. Factor 1 from
a principal components analysis performed on both species combined is highly age correlated and
accounts for approximately 30 percent of total age variation. Factor 2, though also age correlated,
accounts mainly for interspecific difference. The first factors from analyses on each species
separately account for about 50 percent of total age variation whereas second factors are age
independent and account for much of the difference between sexes. Discrimination between the
species improved with increasing age of specimens. Sexual dimorphism is not very pronounced
in either species. Mandibular measurements separate the species and the sexes less well than the
cranial variables. Canonical correlation analysis showed that length, width, height, cranial and
mandibular measurements convey similar information about the skull. Second canonical variates
derived from the comparison between length and width measurements separate the species well
and allow a characterization of shape for each group through the interpretation of the loadings on
the canonical variates. Multiple regression analysis was used to predict age from skull