Dr. Javier Lázaro Tapia

Proximate causes and consequences of seasonal changes in brain size in the common shrew

The study of intra-specific variation in brain size and structure, together with ontogenic and plastic changes, can help us to better understand the mechanisms beneath the evolution of the central nervous system, responsible for complex behavior and cognition in vertebrates. A remarkable case of intra-specific brain variation is the so called Dehnel effect, mainly described in Sorex shrews. These animals undergo a reduction in brain size during autumn, with a minimum size in winter which means a decrease of around 20%; this is followed by a partial re-growth in spring. Furthermore, different brain regions change differently along the year, which suggests a structural change rather than a simple proportional size reduction. The reasons for and the implications of these changes on the behavior and general biology of these small mammals along their life cycle remain unknown.

In my Phd I aim to investigate this phenomenon from a multi-disciplinary approach, including morphology, neurology, and behavior. Our model species is the common shrew Sorex araneus. One of our main aims is to describe the changes at the individual level.  We analyze x-ray images of recaptured wild shrews to monitor the changes in braincase. This method allows us to provide evidence of changes at the individual level, so the process is not confounded to average changes at the population level. Another approach intends to investigate the seasonal changes in brain size, that is, the possible changes in the nervous tissue at a microscopic level. We use histological methods to study brain micro-architecture, including density cell numbers and structure of individual neurons. A change in these features could have implications in neural connectivity, and thus will allow predicting changes/limitations in behavior as a consequence of the change in brain size. Therefore, the last approach aims to study the effect of seasonal brain changes on behavior. This includes cognitive abilities, which we quantify with using maze-like cognitive tests.

In addition, in order to study the possible geographic variation of the Dehnel effect we catch animals from two different, distant populations. Here, we place our traps in the fields and woodlands surrounding our Institute in Möggingen (MPIO Radolfzell); the second trapping site is located in the depths of the Biebrza National Park (Poland), where we use a field station in Gugny (University of Białystok).