COGNITIVE AND BEHAVIORAL ECOLOGY LAB
Food-caching chickadees rely on food caches to survive winter, when naturally available food is limited and unpredictable. More harsh winter conditions should be associated with higher dependence on food caches and on spatial memory used in retrieval of food caches. Spatial memory, in turn, depends on the hippocampus. We tested a hypothesis that harsher winter environment is associated with better spatial memory and larger hippocampus using 10 populations of black-capped chickadees (Roth & Pravosudov 2009; Roth et al. 2011, Roth et al. 2012; Pravosudov & Roth 2013).
Work done by my postdoc Tim Roth II.
Environment, food caching, spatial memory and the hippocampus
Climate along lattitudinal gradient
Climate along lattitudinal gradient
Moving from south to north is associated with (1) lower winter temperatures, (2) more snow and (3) shorter day length.
The hippocampus
Both hippocampus volume and the total number of hippocampal neurons show a signficant increase along a lattitudinal gradient. Chickadee living in environments with more severe winter conditions have larger hippocampi and a larger number of hippocampal neurons.
Controlling for day length
Controlling for day length
Winter climate is also predictably different along the same longitude, but day length is similar.
The Hippocampus
Both hippocampus volume and the total number of hippocampal neurons are larger in chickadees living in colder climate, regardless of day length.
Common Garden Experiment
Common Garden Experiment
To investigate whether differences in memory and the hippocampus between northern and southern populations were due to direct differences in experiences and environment, we performed a 'common garden' experiment. If birds reared and mainained in a 'common garden' or the same lab environment show the sam differences as the wild birds, the effect of expeirence is not likely the cause for these differences.
Common garden experiment
Young from Alaska and Kansas were collected from the nest before they open their eyes and were hand-reared in the same conditions.
While the hippocampus volume in lab-reared birds was not different between Alaska and Kansas chickadees, the total number of hippocampal neurons and hippocampal neurogenesis rates were sigbnfciantly different. Moreover, the total number of hippocampal neurons and hippocampal neurogenesis rates in 'common garden' birds were similar to those in wild birds from the same populations. So despite spending their entire life in the lab, lab-reared chickadees has similar number of neurons and similar neurogenesis rates to birds from the wild. These results support the idea that differences between Alaska and Kansas chickadees is mainly driven by some heritable mechanisms.
Common garden experiment