Merkling Thomas, Perrot Charlotte, Helfenstein Fabrice, Ferdy Jean-Baptiste, Gaillard Laurent, Lefol Emilie, Voisin Emmanuelle, Hatch Scott A, Danchin Etienne, Blanchard Pierrick
CNRS ENFA UMR 5174 EDB (Laboratoire Évolution & Diversité Biologique) Université Toulouse 3 Paul Sabatier 118 route de Narbonne F-31062 Toulouse France.
Present address: CEFE UMR 5175 CNR SEPHE Université de Montpellier Université Paul-Valéry Montpellier 1919 Route de Mende 34293 Montpellier Cedex 5 France.
Ecol Evol. 2016 May 3;6(11):3699-3710. doi: 10.1002/ece3.1777. eCollection 2016 Jun.
Maternal effects occur when the mother's phenotype influences her offspring's phenotype. In birds, differential allocation in egg yolk components can allow mothers to compensate for the competitive disadvantage of junior chicks. We hypothesize that the parent-older chick conflict peaks at intermediate conditions: parents benefit from the younger chick(s) survival, but its death benefits the older chick in terms of growth and survival. We thus expect maternal compensation to follow a bell-shaped pattern in relation to environmental conditions. We studied a black-legged kittiwake () population where previous results revealed increased allocation of yolk testosterone in younger as compared to older chicks in intermediate conditions, in line with our theoretical framework. We therefore predicted a maternally induced increase in aggressiveness, growth, and survival for younger chicks born in intermediate environmental conditions. Controlling for parental effects and chick sex, we manipulated food availability before egg laying to create a situation with intermediate (Unfed group) and good (Fed group) environmental conditions. Within each feeding treatment, we further created experimental broods where the natural hatching order was reversed to maximize our chances to observe an effect of feeding treatment on the younger chicks' aggressiveness. As predicted, we found that chick aggressiveness was higher in younger chicks born from the Unfed group (i.e., in intermediate environmental conditions), but only when they were put in a senior position, in reversed broods. Predictions on growth and survival were not confirmed. Mothers thus seem to favor the competitiveness of their younger chick in intermediate conditions via egg yolk components, but our study also suggests that hatching asynchrony need to be small for maternal compensation to be efficient. We emphasize the need for further studies investigating other chick behaviors (e.g., begging) and focusing on the relative role of different yolk components in shaping parent-offspring conflict over sibling competition.
当母亲的表型影响其后代的表型时，就会出现母体效应。在鸟类中，蛋黄成分的差异分配可以使母亲弥补幼雏的竞争劣势。我们假设亲代与年长雏鸟之间的冲突在中等条件下达到峰值：亲代从较年幼雏鸟的存活中受益，但较年幼雏鸟的死亡在生长和存活方面对年长雏鸟有利。因此，我们预计母体补偿会随着环境条件呈钟形模式。我们研究了一个黑脚三趾鸥种群，先前的研究结果表明，在中等条件下，与年长雏鸟相比，年幼雏鸟的蛋黄睾酮分配增加，这与我们的理论框架一致。因此，我们预测，在中等环境条件下出生的年幼雏鸟，其攻击性、生长和存活率会因母体诱导而增加。在控制亲代效应和雏鸟性别的情况下，我们在产卵前操纵食物供应，以创造中等（未喂食组）和良好（喂食组）环境条件的情况。在每种喂食处理中，我们进一步创建了实验性育雏组，将自然孵化顺序颠倒，以最大限度地增加我们观察喂食处理对年幼雏鸟攻击性影响的机会。正如预测的那样，我们发现，从未喂食组出生的年幼雏鸟（即在中等环境条件下）的攻击性更高，但只有当它们在颠倒的育雏组中处于年长位置时才会如此。关于生长和存活的预测未得到证实。因此，母亲似乎在中等条件下通过蛋黄成分来促进年幼雏鸟的竞争力，但我们的研究也表明，孵化异步性需要很小，母体补偿才会有效。我们强调需要进一步研究调查其他雏鸟行为（如乞食），并关注不同蛋黄成分在塑造亲代与子代在同胞竞争中的冲突方面的相对作用。
