Reproductive resilience and trade-offs: Egg component allocation under nutritional constraints in Japanese Quail

Under natural conditions, organisms regularly experience seasonal or unpredictable fluctuations in their diet that may shape the quantity and quality of their reproduction. While these dietary shifts are known to influence overall reproductive output, their specific effects on the proportional composition of egg components remain unexplored. To partially simulate the natural conditions, we conducted two trials using adult Japanese Quails ( Coturnix japonica ) to examine how dietary restriction and unpredictable feeding influence the proportional composition of egg components. In the first trial, quails were assigned to one of four treatments: full-fed (control) or restricted feeding at 20% (DR20), 30% (DR30), and 40% (DR40) below daily intake. In the second trial, quails were assigned to one of three treatments: full feeding (control), constant 40% restriction (DR40), or unpredictable feeding schedule (UNPR). Each trial lasted for 14 days, and birds were housed individually. Severe dietary restrictions (DR30, DR40) reduced albumen and shell mass, shell thickness, and egg volume. However, yolk mass, yolk color, egg shape index, and shell density remained unaffected across all dietary levels. Severe restrictions also increased the yolk ratio while reducing the albumen ratio, suggesting that birds may evolutionarily prioritize yolk deposition to sustain reproductive functions. However, reduced albumen content due to maternal nutritional stress may also limit essential nutrients, and disrupt the embryo's osmoregulation, which ultimately affects offspring quality. Reduced shell contents at the severe restriction levels can affect the egg's ability to provide physical protection, regulate gas exchange and control water loss, thereby influencing embryonic development. In contrast, moderate restriction (DR20) and unpredictable feeding (UNPR) had no effect on any of the egg traits. These findings suggest that quails strategically allocate resources among egg components under dietary constraints, indicating potential trade-offs in reproductive investment. The resilience observed under moderate restriction and unpredictability underscores the species' adaptive capacity in fluctuating environments.