Data from: Profound reversible seasonal changes of individual skull size in a mammal

Postnatal size changes in most vertebrates are unidirectional and finite
once the individual reaches full size. In rare cases, changes of body
length may occur in response to harsh environmental conditions. Such
reactionary changes are distinct from seasonal, often anticipatory
morphological changes, such as the reversible size change of some adult
bird brains. A unique pattern of profound anatomical change known as
Dehnel’s phenomenon has been described for the body, skull and brain size
of red-toothed shrews and some mustelids. The seasonal 20% decrease and
15% re-growth of the most common proxy, braincase height, were documented
at population level from extracted skulls post-mortem. Quantifying
intra-individual change had so far been methodologically prohibitive.
Here, we followed the intra-individual change in skull size and body mass
throughout the full cycle in wild recaptured shrews (Sorex araneus). Using
X-ray images we showed that individuals decreased the size of their
braincases in anticipation of winter by an average of 15.3%. Braincases
then partially regrew in spring by 9.3%. Body mass decreased by 17.6% and
then dramatically increased by 83.4% in spring. Thus, we demonstrate that
the dramatic changes incurred by Dehnel’s phenomenon occur in the
individual’s bone and other tissues.