Natural photoperiodic regulation of hippocampal neural plasticity in wild male and female black-capped chickadees (Poecile atricapillus)

Abstract

Food storing, a hippocampus-dependent spatial behaviour, fluctuates seasonally in black-capped chickadees (Poecile atricapillus), who store more food in the fall months for later retrieval in the resource-scarce winter. Supporting this behavioural plasticity is hippocampal neural plasticity. However, previous studies on how the hippocampus changes seasonally are inconsistent; it appears captivity may contribute to this variability. Here, I examined seasonal patterns of hippocampal plasticity in wild, non-captive male and female black-capped chickadees (N=36 adults). While hippocampal plasticity in males was minimal, female chickadees captured in winter (December-January) had increased hippocampal neurogenesis (measured using doublecortin immunoreactivity) compared to females captured in March-April and August-September. While sex differences in brain and behaviour are observed in some avian and non-avian species, these data are the first evidence of sex differences in the hippocampus of black-capped chickadees, and suggest there may winter-specific physiological and social pressures borne only by females which require specialized neural infrastructure.