Darkness modifies brain cell proliferation and behavior in female <i>Austrolebias reicherti</i> fish

Sensory systems adapt to environmental change through behavioral and neurogenic plasticity. We examined brain cell proliferation in sensory structures in response to long-lasting sustained darkness. Female Austrolebias reicherti were exposed to continuous darkness or natural light-dark cycle for 45 days. At the end of this conditioning period, sensory clues involved in sexually oriented behaviors and brain proliferation were compared between groups. To assess functional implications, a dual choice test was performed under different sensory conditions (visual and olfactory) using conspecifics or heterospecific (same genus) males. To evaluate proliferation individuals received a single BrdU injection three days before fixation. BrdU+ cells were evaluated in the brain and their density distribution quantified in the optic tectum (TeO), torus longitudinalis (TL), and olfactory bulb (OB). Cell proliferation in dark-maintained females was greater in the OB, whereas cell proliferation in light-maintained females was greater in the TeO and TL. Concordantly, females in the darkness condition were better at identifying conspecifics using smell than those in the light condition, while those in the light condition were better at identifying conspecifics using vision than those in darkness. The brain optimized to function most effectively under specific light conditions, adjusting cell proliferation to reinforce neural sensory circuits with greatest demand. In conclusion, the average strength of sustained darkness conditions modulates neurogenesis in key sensory brain regions and influences female's ability to discriminate between conspecific and heterospecific. Sensory plasticity in response to environmental variability may play a crucial role in adaptive and evolutionary processes in this species.