| Postnatal neurogenesis in wild mammals may play an essential role in spatial memory. I compared two species that differ in their reliance on memory for where food is stored for future consumption. Yellow-pine chipmunks use a single cache to store winter food, whereas eastern grey squirrels use multiple storage sites. In chipmunks, the density of newborn cells in the dentate gyrus was negatively related to the plasma corticosterone concentration, and densities of newborn and young neurons were negatively related to the neutrophil:lymphocyte ratio. No such relationships were found in squirrels. I suggest that the independence in squirrels of cell densities and indicators of condition is an adaptation that prevents decreases in neurogenesis. As compared to chipmunks, squirrels had three times the density of newborn cells in the dentate gyrus, but did not differ in density of young neurons. I discuss four explanations to account for this inconsistency. |
