Abstract
Studies on the yolk and albumen content in bird eggs, and the effects of variations in their relative loads in the phenotype of the birds, have revealed multiple consequences at different levels of biological organization, from biochemical traits to behavior. However, little is known about the effect of albumen variation on energetics performance during development and early ontogeny, despite the fact that variation in energy expenditure may have consequences in terms of fitness for both feral and domestic species. In this work, we evaluated experimentally whether variations in the content of albumen of Gallus gallus eggs could generate differences in metabolic rates during embryonic development. Additionally, we assessed changes in the activity of mitochondrial enzymes (cytochrome c oxidase and citrate synthase) in skeletal muscles and liver. Finally, we evaluated the success of hatching of these embryos and their metabolic rates (MR) post-hatching. The results revealed a significant reduction in MR in the last fifth of embryonic life, and reduced catabolic activities in the skeletal muscle of chicks hatched from albumen-removed eggs. However, the same group demonstrated an increase in catabolic activity in the liver, suggesting the existence of changes in energy allocation between tissues. Besides, we found a decrease in hatching success in the albumen-removed group, suggesting a negative effect of the lower albumen content on eggs, possibly due to lower catabolic activities in skeletal muscle. We also found a compensatory phenomenon in the first week after hatching, i.e., birds from albumen-removed eggs did not show a decrease in MR either at thermoneutral temperatures or at 10°C, compared to the control group. Collectively, our data suggest that a reduction in albumen may generate a trade-off between tissue metabolic activities, and may explain the differences in metabolic rates and hatching success, supporting the immediate adaptive response (IAR) hypothesis.
Highlights
During embryonic development, animals may demonstrate a more than 100-fold increase in body mass, with a paralleled dramatic rise in metabolic rate (Vleck and Vleck, 1980)
A second hypothesis, called predictive adaptive response (PAR), postulates that environmental cues encountered during early life may modify embryonic development in order to cope with predicted environmental conditions in later life
Mass-specific resting metabolic rates of developing animals were statistically indistinguishable between all groups until E16, at which stage RMR was lower in the albumen-removed group relative to the control group and sham group (Pt; p = 0.002 and p = 0.031, respectively, Figure 1)
Summary
Animals may demonstrate a more than 100-fold increase in body mass, with a paralleled dramatic rise in metabolic rate (Vleck and Vleck, 1980). It has been hypothesized that nutrient-poor embryonic environments generate compromises in fetal development through energy reallocations (trade-offs) between organs or tissues (e.g., brain growth at the expense of non-vital organs) This hypothesis has been referred to as the immediate adaptive response (IAR; Bateson et al, 2004). We hypothesized that a decrease in the embryonic protein source, by means of the removal of a portion of albumen, could generate differences in metabolic rates during embryonic development, due to reallocations of energy and nutrients between tissues (i.e., supporting the IAR hypothesis). We expected these changes to produce effects in early ontogeny due to trade-offs generated during embryonic growth. We aimed to determine both resting metabolic rates and metabolic rates under a thermoregulatory challenge in 1 week old chicks, to analyze the potential energetic consequences on early ontogeny
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