Primary data on skull and brain morphology for: Geographical patterns in seasonal changes of body mass, skull, and brain size of common shrews

Some small mammals exhibit Dehnel’s Phenomenon, a drastic decrease in body
mass, braincase and brain size from summer to winter, followed by regrowth
in spring. This is accompanied by a reorganization of the brain and
changes in other organs. The evolutionary link between these changes and
seasonality remains unclear, although the intensity of change varies
between locations as the phenomenon is thought to lead to energy savings
during winter. Here we explored geographic variation of the intensity of
Dehnel’s Phenomenon in Sorex araneus. We compiled literature on seasonal
changes in braincase size, brain and body mass, supplemented by our own
data from Poland, Germany, and the Czech Republic. We analysed the effect
of geographic and climate variables on the intensity of change and
patterns of brain reorganization. From summer to winter the braincase
height decreased by 13%, followed by 10% regrowth in spring. For body mass
the changes were -21%/+82%, respectively. Changes increased towards
northeast. Several climate variables were correlated with these
transformations, confirming a link of the intensity of the changes with
environmental conditions. This relationship differed for the decrease vs.
regrowth, suggesting that they may have evolved under different selective
pressures. We found no geographic trends explaining variability in the
brain mass changes although they were similar (-21%/+10%) to those of the
braincase size. Underlying patterns of change in brain organisation in
north-eastern Poland were almost identical to the pattern observed in
southern Germany. This indicates that local habitat characteristics may
play a more important role in determining brain structure than broad scale
geographic conditions. We discuss the techniques and criteria used for
studying this phenomenon, as well as its potential presence in other taxa
and the importance of distinguishing it from other kinds of seasonal
variation.