Data from: Laying sequence interacts with incubation temperature to influence rate of embryonic development and hatching synchrony in a precocial bird

Incubation starts during egg laying for many bird species and causes developmental asynchrony within clutches. Faster development of late-laid eggs can help reduce developmental differences and synchronize hatching, which is important for precocial species whose young must leave the nest soon after hatching. In this study, we examined the effect of egg laying sequence on length of the incubation period in Wood Ducks (Aix sponsa). Because incubation temperature strongly influences embryonic development rates, we tested the interactive effects of laying sequence and incubation temperature on the ability of late-laid eggs to accelerate development and synchronize hatching. We also examined the potential cost of faster development on duckling body condition. Fresh eggs were collected and incubated at three biologically relevant temperatures (Low: 34.9°C, Medium: 35.8°C, and High: 37.6°C), and egg laying sequences from 1 to 12 were used. Length of the incubation period declined linearly as laying sequence advanced, but the relationship was strongest at medium temperatures followed by low temperatures and high temperatures. There was little support for including fresh egg mass in models of incubation period. Estimated differences in length of the incubation period between eggs 1 and 12 were 2.7 d, 1.2 d, and 0.7 d at medium, low and high temperatures, respectively. Only at intermediate incubation temperatures did development rates of late-laid eggs increase sufficiently to completely compensate for natural levels of developmental asynchrony that have been reported in Wood Duck clutches at the start of full incubation. Body condition of ducklings was strongly affected by fresh egg mass and incubation temperature but declined only slightly as laying sequence progressed. Our findings show that laying sequence and incubation temperature play important roles in helping to shape embryo development and hatching synchrony in a precocial bird.多数鸟类会在产卵期间启动孵化，这会导致窝内胚胎发育不同步。晚产卵卵的发育速度更快，可缩小胚胎发育差异并同步孵化，这对幼鸟孵化后需尽快离巢的早成鸟（precocial）物种而言尤为重要。本研究以林鸭（Aix sponsa）为对象，探究产卵顺序对其孵化期时长的影响。由于孵化温度对胚胎发育速率具有显著调控作用，本研究进一步检验了产卵顺序与孵化温度的交互效应，及其对晚产卵卵加速发育、同步孵化能力的影响。本研究同时探究了发育速度加快对雏鸟身体状况的潜在代价。研究人员采集新鲜卵粒，在三种符合生态学意义的温度（低温：34.9℃、中温：35.8℃、高温：37.6℃）下进行孵化，并设置了1至12号的产卵顺序梯度。孵化期时长随产卵顺序推进呈线性缩短，但该相关性在中温条件下最为显著，其次为低温与高温条件。孵化期时长模型中加入新鲜卵重的支持度极低。在中温、低温与高温条件下，1号卵与12号卵的孵化期时长预估差异分别为2.7天、1.2天与0.7天。仅在中等孵化温度条件下，晚产卵卵的发育速率提升幅度足以完全弥补林鸭窝卵在完全孵化启动时所呈现的自然发育异步水平。雏鸟身体状况受新鲜卵重与孵化温度的影响显著，但随产卵顺序推进仅出现小幅下降。本研究结果表明，产卵顺序与孵化温度在塑造早成鸟的胚胎发育与孵化同步性方面发挥着关键作用。