STUDIES OF NATURAL POPULATIONS OF MUS. IV. SKELETAL VARIATIONS

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Abstract
The skeletons of 342 house mice, M. musculus, collected over a 4-yr. period in southeastern Michigan, were examined for 24 skull variants and 1 vertebral characteristic. A comparison of the samples for all 25 characteristics revealcd that 1, the sample from the geographic center of the trapplng localities, differed significantly (5% level) from the rest. When each characteristic was considered independently, not only were significant differences found between some localities, but also in several localities significant annual fluctuations were observed. No correlation was observed between the geographic remoteness of 2 samples and the degree of divergence. Genetic drift and/or differences in subtle selective forces were considered as the most obvious causal agents of the frequency variations observed. No definite conclusions were reached. However, data from other loci which suggest the existence of small breeding units favor genetic drift as the major factor responsible for skeletal variations. Finally, the pooled Ann Arbor [Michigan, USA] sample was compared with data of 12 samples from other parts of the world.