117.4 Saturday, Jan. 7 Gene expression underlying the “decision” to initiate egg-laying: Social effects on vitellogenesis PERFITO, Nicole*; HORNICK, Kristin; NGUYEN, Sophie; DARLING, Hannah; BENTLEY, George; UC Berkeley; UC Berkeley; UC Berkeley; UC Berkeley; UC Berkeley email@example.com
The ‘decision’ by female birds to begin egg-laying is a pivotal physiological time point in reproductive timing. Once rapid final maturation of follicles begins, including the incorporation of yolk, the female is committed physiologically to a major energetic investment. While decades’-worth of ecological data correlate lay dates in the field with environmental variables (e.g. temperature), and experimental work demonstrates advancement or delay of lay dates, we understand very little about the physiological mechanisms regulating this major life-history transition. We exposed female European starlings (Sturnus vulgaris) to natural changes in photoperiod with differing social cues and measured gene expression in the hypothalamus, anterior pituitary gland, liver and developing ovarian follicles. A group of females was housed in outdoor aviaries with access to mates, nest boxes and ad libitum food and water. A second group was housed in identical conditions but without physical access to mates. Under 12 hour days, both groups began initial follicle development and had slightly elevated liver vitellogenin (VTG) expression. Two weeks later (12.6L), females housed with males began final follicle maturation, had begun oviposition and had elevated VTG expression. On the same day, females in an adjacent aviary without access to males showed no progression past initial follicle development, and had low VTG expression. Subsequently, males were introduced to female-only aviaries. After eight days, newly paired females had begun final maturation and had elevated VTG expression. These data are the first to demonstrate a social effect on VTG expression, and will help to tease apart effects of photoperiod and social interactions on multiple components of the HPG axis.