Abstract

Differences in the deposition of limited maternal resources to eggs can reflect optimal 26 allocation to manipulate offspring phenotype, or constraints caused by maternal 27 condition. We examined multiple maternal substances transferred to eggs in the 28 magpie Pica pica to test the hypothesis that certain substances represent constraint 29 and some optimal allocation. We did this by supplementary feeding magpies prior to 30 egg-laying and then comparing the effect of food on maternal substances in 31 conjunction with laying order relative to a control group. Certain substances such as 32 carotenoids, immunglobulins and avidin responded positively to food supplementation, 33 whereas others such as testosterone and total protein content of eggs did not. 34 Immunoglobulins allocation increased with laying order in fed, but not in unfed groups. 35 By contrast, avidin showed the reverse pattern. Our results suggest that patterns of 36 optimal allocation and constraint in maternally-provisioned substances co-occur within 37 clutches. Furthermore, constraint and optimal allocation may co-occur within the same 38 substance i.e.