Relationships among Fresh Mass, Incubation Time, and Water Loss in Japanese Quail Eggs

Egg size is commonly assumed to increase the fitness value of hatchlings, and yet, most intraspecific variation in egg size appears to be highly heritable. Because traits strongly associated with fitness are expected to have low heritabilities, these two observations are not mutually compatable unless other factors act to offset the fitness value of large eggs. In this paper, we assess the influence of intraspecific egg-size variation on incubation periods and rates of egg water loss among Japanese Quail (Coturnix japonica) eggs. In contrast to interspecific studies of these relationships, we observed very low correlations between the logarithms of fresh egg mass and incubation time (r2 = 0.016, P = 0.01, n = 378) and between fresh egg mass and daily water loss (r2 = 0.028, P = 0.03, n = 163). Analysis of fresh eggs and newly hatched chicks confirmed that heavier eggs lost proportionately less water during incubation. These observations suggest that statistical relationships derived from interspecific comparisons of egg size and egg physiology are not generally applicable to studies of intraspecific egg-size variation.