Most studies on hippocampus-behaviour relationships focus on lab species. From an evolutionary perspective this is problematic because the effects of natural selection are removed and captive breeding results in permanent effects on brain anatomy. Thus, to properly understand the correlated evolution of the hippocampus and behaviour, it is necessary to examine wild populations.
Unlike previously studied species, Richardson's ground squirrel (Urocitellus richardsonii), lives socially in matrilineal kin groups, but has a polygamous mating system. Richardson's ground squirrel also has prominent sexual dimorphisms in several behaviours as well as major seasonal variations in behaviour due to its hibernation cycle. Current theory and the socioecology of this species predicted that males would have larger hippocampal volumes than females and this difference would be greatest in the breeding season. In contrast, we found that the hippocampus was largest in non-breeding males (Burger et al., 2013). In subsequent studies, we found significant seasonal and sex differences in hippocampal neurogenesis (Burger et al., 2014) and the sizes of several non-hippocampal brain regions (Keeley et al., 2015).
Currently, this research has expanded to include neuronal morphology. With the combination of a Neurolucida neuron tracing system and our slide scanner, we are analyzing the size and complexity of pyramidal neurons and granule cells in the hippocampus of male and females Richardson's ground squirrels during both breeding and non-breeding seasons.