Elevation-related differences in memory and the hippocampus in mountain chickadees, Poecile gambeli

Harsh environments may lead to increased demands on memory in animals that rely on memory for survival. We previously showed that winter severity is associated with non-experience-based differences in memory and the hippocampus over a large continental scale in food-caching black-capped chickadees, Poecile atricapillus. However, large climatic differences also occur along steep elevational gradients in montane environments over a small geographical scale. Here, we demonstrate for the first time that large differences in memory and the hippocampus exist over extremely short distances (10 km) along the elevation gradient. We found that food-caching mountain chickadees (P. gambeli) from the highest elevations in the Sierra Nevada Mountains had significantly better spatial memory associated with larger hippocampi, with almost twice the number of hippocampal neurons, than individuals only 600 m lower in elevation. We found similarly large differences in hippocampal neurogenesis rates as indicated by the total number of immature neurons. Our study therefore suggests that climate-related environmental differences can produce dramatic differences in memory and the hippocampus in animals within close proximity on small spatial scales and that currently observed trends in global climate may have significant effects on cognition and the brain.