Variation in brain regions associated with fear and learning in contrasting climates

In environments where resources are difficult to obtain and enhanced cognitive capabilities might be adaptive, brain structures associated with cognitive traits may also be enhanced. In our previous studies, we documented a clear and significant relationship among environmental conditions, memory and hippocampal structure using ten populations of black-capped chickadees (Poecile atricapillus) over a large geographic range. In addition, focusing on just the two populations from the geographical extremes of our large-scale comparison, Alaska and Kansas, we found enhanced problem-solving capabilities and reduced neophobia in a captive-raised population of black-capped chickadees originating from the energetically demanding environment (Alaska) relative to conspecifics from the milder environment (Kansas). Here, we focused on three brain regions, the arcopallium (AP), the nucleus taeniae of the amygdala and the lateral striatum (LSt), that have been implicated to some extent in aspects of these behaviors in order to investigate whether potential differences in these brain areas may be associated with our previously detected differences in cognition. We compared the variation in neuron number and volumes of these regions between these populations, in both wild-caught birds and captive-raised individuals. Consistent with our behavioral observations, wild-caught birds from Kansas had a larger AP volume than their wild-caught conspecifics from Alaska, which possessed a higher density of neurons in the LSt. However, there were no other significant differences between populations in the wild-caught and captive-raised groups. Interestingly, individuals from the wild had larger LSt and AP volumes with more neurons than those raised in captivity. Overall, we provide some evidence that population-related differences in problem solving and neophobia may be associated with differences in volume and neuron numbers of our target brain regions. However, the relationship is not completely clear, and our study raises numerous questions about the relationship between the brain and behavior, especially in captive animals.