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First published online November 10, 2003

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The metabolic cost of avian egg formation: possible impact of yolk precursor production?

François Vézina^*, Katrina G. Salvante and Tony D. Williams

Department of Biological Sciences, Simon Fraser University, Burnaby, 8888 University Drive, Burnaby, V5A 1S6, Canada

View larger version (19K): [in a new window]   Fig. 1. (A) Experimental estradiol injection protocol to determine the pattern of vitellogenin production in response to the treatment. (B) Experimental injection and resting metabolic rate (RMR) protocol to determine the potential metabolic cost of yolk precursor production. The numbers represent the days into the treatment, with the white sections symbolizing daytime and dark sections symbolizing night-time. The arrows represent either RMR measurement, injection or blood sampling time.

View larger version (9K): [in a new window]   Fig. 2. Pattern of circulating vitellogenin (VTG) measured daily during experiment 1. Horizontal lines indicate significant differences between VTG levels in birds measured on different days. Values are means + S.E.M. `Day' corresponds to day in Fig. 1A. NB refers to non-breeding values. **P<0.005, ***P<0.0005. Vitellogenin plasma levels for days 2–6 were all significantly different from NB values (P<0.0005 in all cases).

View larger version (13K): [in a new window]   Fig. 3. (A) Plasma vitellogenin (VTG) and (B) very-low-density lipoprotein (VLDL) levels measured at pre-, mid- and post-treatment in estradiol (E2)-treated (filled bars) and sham groups (open bars). Values are means + S.E.M. Comparisons were made between E2 and sham treatment groups at pre-, mid- and post-treatment. *P<0.05, **P<0.005, ***P<0.0005. See text for statistics and within-treatment-group differences.

View larger version (9K): [in a new window]   Fig. 4. Comparison of least-squared mean resting metabolic rate (RMR; correcting for the effect of body mass and time) between estradiol (E2)-treated (filled bars) and sham groups (open bars) at pre- and mid-treatment. Values are means + S.E.M.