Ndithia Henry K, Bakari Samuel N, Matson Kevin D, Muchai Muchane, Tieleman B Irene
Ornithology Section, Department of Zoology, National Museums of Kenya, P.O. Box 40658 -00100 GPO, Nairobi, Kenya.
Groningen Institute for Evolutionary Life Sciences, University of Groningen, P.O. Box 11103, 9700 CC Groningen, The Netherlands.
Front Zool. 2017 May 26;14:28. doi: 10.1186/s12983-017-0213-1. eCollection 2017.
Variation in growth and immune function within and among populations is often associated with specific environmental conditions. We compared growth and immune function in nestlings of year-round breeding equatorial Redcapped Lark from South Kinangop, North Kinangop and Kedong (Kenya), three locations that are geographically close but climatically distinct. In addition, we studied growth and immune function of lark nestlings as a function of yearround variation in breeding intensity and rain within one location. We monitored mass, wing, and tarsus at hatching (day 1) and at 4, 7, and 10 days posthatch, and we quantified four indices of immune function (haptoglobin, agglutination, lysis and nitric oxide) using blood samples collected on day 10.
Nestling body mass and size at hatching, which presumably reflect the resources that females allocated to their eggs, were lowest in the most arid location, Kedong. Contrary to our predictions, nestlings in Kedong grew faster than nestlings in the two other cooler and wetter locations of South and North Kinangop. During periods of peak reproduction within Kedong, nestlings were heavier at hatching, but they did not grow faster over the first 10 days posthatch. In contrast, rainfall, which did not relate to timing of breeding, had no effect on hatching mass, but more rain did coincide with faster growth posthatch. Finally, we found no significant differences in nestling immune function, neither among locations nor with the yearround variation within Kedong.
Based on these results, we hypothesize that female body condition determines nestling mass and size at hatching, but other independent environmental conditions subsequently shape nestling growth. Overall, our results suggest that environmental conditions related to food availability for nestlings are relatively unimportant to the timing of breeding in equatorial regions, while these same conditions do have consequences for nestling size and growth.
种群内部和种群之间生长与免疫功能的差异通常与特定环境条件相关。我们比较了来自肯尼亚南基南戈普、北基南戈普和凯东这三个地理位置相近但气候不同的地区的常年繁殖的赤道红顶云雀雏鸟的生长和免疫功能。此外，我们研究了一个地区内云雀雏鸟的生长和免疫功能与全年繁殖强度和降雨变化的关系。我们在雏鸟孵化时（第1天）以及孵化后4、7和10天监测了它们的体重、翅长和跗跖长，并使用第10天采集的血样对免疫功能的四个指标（触珠蛋白、凝集、裂解和一氧化氮）进行了量化。
孵化时雏鸟的体重和体型可能反映了雌鸟分配给卵的资源，在最干旱的地区凯东最低。与我们的预测相反，凯东的雏鸟比南基南戈普和北基南戈普另外两个较凉爽湿润地区的雏鸟生长得更快。在凯东繁殖高峰期，雏鸟孵化时体重更重，但在孵化后的前10天内它们并没有生长得更快。相比之下，与繁殖时间无关的降雨对孵化时的体重没有影响，但更多降雨与孵化后更快的生长相吻合。最后，我们发现雏鸟的免疫功能在不同地区之间以及凯东地区内全年变化中均无显著差异。
基于这些结果，我们推测雌鸟的身体状况决定了雏鸟孵化时的体重和体型，但其他独立的环境条件随后会影响雏鸟的生长。总体而言，我们的结果表明，与雏鸟食物供应相关的环境条件对赤道地区繁殖时间的影响相对较小，而这些条件确实会对雏鸟的体型和生长产生影响。
