Ph.D. Advisor: Dr. Tony D. Williams, SFU

Collaborators: Dr. Rosemary L. Walzem, Texas A&M

                          Dr. Norbert H. Hanuerland, SFU

                          Dr. Francois Vezina, UQAR

Animals require energy to fuel all aspects of life, including locomotion, thermoregulation, reproduction, and general maintenance.  Trade-offs arise between these activities when resources and energy are limited. One such trade-off is that between survival and current reproduction, which may occur when the amount of resources a female can provide her offspring is limited by her own energetic needs. This trade-off is of great consequence when periods of reproductive activity coincide with periods of increased energy demand or decreased energy availability brought about by fluctuations in environmental factors.

Because free-living birds generally time reproduction to coordinate the chick-rearing period with the seasonal peak in food availability, females are often faced with challenging environmental conditions earlier in the season during egg production. I examined the differential allocation of energy-rich lipids to self-maintenance versus reproductive output during avian egg production in favorable versus energetically-challenging conditions.

I acclimated zebra finches (Taeniopygia guttata) to different ambient temperatures (7°C and 21°C) and measured resting metabolic rate in non-breeding and laying females, maternal lipid parameters, parental food intake, activity, and body condition, number and size of eggs laid, and lipid and protein content of the eggs.

Egg composition analysis

I validated a poultry-based assay for particle diameter distribution (PDD) of very-low density lipoprotein (VLDL) for use in passerine birds. VLDL particles transport lipids throughout the body and can be classified as small yolk-targeted VLDL (VLDLy) and larger generic VLDL particles, which fuel self-maintenance activities. In favorable conditions VLDL PDD is positively related to laying rate in chickens and egg size in zebra finches. In contrast, VLDL PDD was not related to the temperature-dependent energetic needs of laying Zebra Finches.

I isolated apo-VLDL-II, a VLDLy apolipoprotein, from egg-laying zebra finch plasma. I had an antibody raised against the N-terminally sequenced protein with the aim of developing a direct assay for circulating VLDLy. This work was continued by Dong Han (Williams Lab).

By elucidating the mechanisms underlying energy allocation during reproduction in energetically- challenging conditions, I hope to better understand the reproductive choices that individuals make.

While egg production at 21°C was associated with a 27% increase in metabolic rate above that of non-breeding females, this increase was small compared to the 130% increase associated with active thermoregulation at 7˚C. Cold-acclimation had no effect on female body condition or circulating lipid levels, but breeding pairs consumed more seed and hopped less when acclimated to 7°C. In spite of these energy-saving responses to the cold, laying females were not able to totally compensate for the increased energy demand brought about by low temperatures; they laid eggs containing 11% less yolk lipid, and thus potentially compromised offspring development.

A breeding pair
of zebra finches

SDS-PAGE gel of

zebra finch VLDL

apolipoproteins

A typical zebra finch nest

Related publications

Salvante, K.G., Vezina, F., and Williams, T.D. 2010. Evidence for within-individual energy reallocation in cold-challenged, egg-producing birds. Journal of Experimental Biology 213:1991-2000.

Salvante, K.G., Walzem, R.L., and Williams, T.D. 2007. What comes first, the Zebra Finch or the egg? Temperature-dependent reproductive, physiological, and behavioural plasticity in egg-laying Zebra Finches. Journal of Experimental Biology. 210:1325-1334.

Salvante, K.G., Lin, G., Walzem, R.L., and Williams, T.D. 2007. Characterization of very-low density lipoprotein particle diameter dynamics in relation to egg production in a passerine bird. Journal of Experimental Biology. 210:1064-1074.

Vezina, F., Salvante, K.G., and Williams, T.D. 2003. The metabolic cost of avian egg formation: Possible impact of yolk precursor production? Journal of Experimental Biology. 206:4443-4451.

Featured in Inside JEB: Journal of Experimental Biology. 206:4381.

Salvante, K.G., and Williams, T.D. 2002. Vitellogenin dynamics during egg-laying: Daily variation, repeatability and relationship with egg size. Journal of Avian Biology. 33:391-398.