Meeting Abstract

89.5  Monday, Jan. 6 14:30  Exactly when do female birds make their ‘timing of breeding’ decision, and what cues do they use? WILLIAMS, TD; Simon Fraser Uni., Burnaby tdwillia@sfu.ca

Current models for control of timing of breeding suggest that day length provides reliable ‘initial predictive information’ for seasonal breeding but that non-photoperiodic ‘supplemental factors’ (temperature, food, social behavior) fine-tune the actual timing of egg-laying. Nevertheless, the cues and physiology controlling when birds decide to lay remain obscure. Past and current research on this problem has been based on the assumption that, “physiological processes do not happen instantly” (Dawson 2007), suggesting that non-photoperiodic cues are more likely to modulate the timing and rate of photoperiodically-induced gonadal maturation over a relatively long time window prior to onset of egg-laying. The alternative: that supplemental cues modulate the exact time of laying only within a short period of full gonadal maturity, has rarely been considered, and then mainly in males. Here I, firstly, propose a model for female birds of “constrained ovarian development” and “release” by non-photoperiod cues immediately (days) before egg-laying. This model suggests that a) even though food and social behaviour might not have long-term predictive value, these could still be key, proximate factors for timing of egg-laying (as proposed by some earlier work, e.g. Perrins 1970), and b) that we need to use different experimental approaches in future work. Secondly, I review data for female European starlings (Sturnus vulgaris) in captivity which suggest that the metabolic switch, from generic VLDL to yolk-targeted VLDLy synthesis, might be the critical component of gonadal maturation to focus on in future experiments in order to identify early on when a female has made her “decision” to proceed with egg-laying.