Data from: Maternal transfer of androgens in eggs is affected by food supplementation but not by predation risk

Mothers may affect the future success of their offspring by varying allocation to eggs and embryos. Allocation may be adaptive based on the environmental conditions perceived during early breeding. We investigated the effects of food supplementation and predation risk on yolk hormone transfer in the pied flycatcher (Ficedula hypoleuca). In a food supplementation experiment, females were food-supplemented prior to and during egg-laying and androgen concentrations were measured throughout the laying order. Predation risk was investigated in three different studies combining both correlative data, where flycatchers bred in close proximity to two different predator species that prey upon adult flycatchers (either Tengmalm's owl, Aegolius funereus or pygmy owl, Glaucidium passerinum), and an experimental manipulation, where flycatchers were exposed to cues of a nest predator (least weasels, Mustela nivalis). Females receiving food supplementation laid eggs with lower concentrations of androstenedione (A4) than females not receiving food supplements. Yolk testosterone (T) concentration showed the same pattern but the difference was not statically significant. Testosterone (but not A4) concentration increased within clutches, from the first to the last egg, independently of the food supplementation. Females breeding under high predation risk did not differ from control females in their yolk androgen levels (A4, T or progesterone). However, concentrations of A4 tended to be lower in the proximity of pygmy owls, which could indirectly increase offspring survival after fledging. Food supplementation during egg-laying seems to have a stronger impact on maternal transfer of androgens than predation risk. Food availability and predation risk could differentially affect the trade-offs of androgen allocation for the offspring when raised in good vs. dangerous environments.

母体可通过调整对卵与胚胎的资源分配，影响后代未来的繁殖成功率。这类资源分配策略可根据繁殖早期感知到的环境条件产生适应性调整。本研究探究了食物补给与捕食风险对斑姬鹟（pied flycatcher, Ficedula hypoleuca）卵黄激素传递的调控效应。在食物补给实验中，研究人员在雌鸟产卵前及整个产卵期为其提供额外食物，并检测了不同产卵顺序下卵内的雄激素浓度。针对捕食风险的探究包含三项独立研究：两项为相关性调查，即选取繁殖巢分别紧邻两种捕食成年斑姬鹟的猛禽物种的种群——分别为鬼鸮（Tengmalm's owl, Aegolius funereus）与花头小鸮（pygmy owl, Glaucidium passerinum）；另一项为操控实验，将斑姬鹟暴露于巢捕食者伶鼬（least weasels, Mustela nivalis）的化学线索中。实验结果显示：相较于未获得食物补给的雌鸟，补给组雌鸟所产卵的雄烯二酮（androstenedione, A4）浓度显著更低。卵黄睾酮（testosterone, T）浓度呈现相同变化趋势，但组间差异未达到统计学显著性水平。无论是否进行食物补给，整窝卵内的睾酮（而非雄烯二酮）浓度均随产卵顺序从第一枚至最后一枚逐渐升高。处于高捕食风险环境下繁殖的雌鸟，其卵内雄激素水平（雄烯二酮、睾酮或孕酮）与对照组雌鸟无显著差异。不过，在靠近花头小鸮的巢区中，卵内雄烯二酮浓度呈现降低趋势，该现象或可间接提升雏鸟出飞后的存活率。综合来看，产卵期的食物补给对母体雄激素传递的调控效应要强于捕食风险。在优质与危险两种不同抚育环境中，食物可获得性与捕食风险会通过差异化路径影响后代雄激素分配的演化权衡。