  Insects exhibit remarkable cognitive skills in the field and several
cognitive abilities have been demonstrated in Drosophila in the laboratory. By
devising an ethologically relevant experimental setup that also allows
comparison of behavior across remote taxonomic groups we sought to reduce the
gap between the field and the laboratory, and reveal as yet undiscovered
ethological phenomena within a wider phylogenetic perspective. We tracked
individual flies that eclosed in a small (45mm) arena containing a piece of
fruit, connected to a larger (130mm) arena by a wide (5mm) doorway. Using this
setup we show that the widely open doorway initially functions as a barrier:
the likelihood of entering the large arena increases gradually, requiring
repeated approaches to the doorway, and even after entering the flies
immediately return. Gradually the flies acquire the option to avoid returning,
spending more relative time and performing relatively longer excursions in the
large arena. The entire process may take up three successive days. This
behavior constitutes coping with space neophobia, the avoidance of untrodden
space. It appears to be the same as the neophobic doorway-crossing reported in
mouse models of anxiety. In both mice and flies the moment-to-moment
developmental dynamics of transition between trodden and untrodden terrain
appear to be the same, and in mice it is taken to imply memory and, therefore,
cognition. Recent claims have been made for a deep homology between the
arthropod central complex and the vertebrate basal ganglia, two structures
involved in navigation. The shared dynamics of space occupancy in flies and
mice might indicate the existence of cognitive exploration also in the flies or
else a convergent structure exhibiting the same developmental dynamics.
