Sex ratio manipulation in response to maternal condition in pigeons: evidence for pre-ovulatory follicle selection

A number of recent reports have documented offspring sex ratio biases in birds. However, to date the potential mechanisms that have been put forward to explain the proximate basis for these deviations are entirely speculative. Using a captive population of domestic pigeons (Columba livia domestica), I tested the hypothesis that mothers in relatively poor physical condition should overproduce daughters by manipulating maternal body condition around the time of egg laying by continuous egg removal and differing feeding regimes. During treatment, females were fed a controlled quantity of food. This, combined with the high energetic costs of repeated egg production caused a significant reduction in maternal body weight. In contrast, during control when food was available ad libitum, maternal body weight did not decline, despite repeated egg production. No significant deviation from parity was evident in the sex ratio of either the first or second eggs during control, whereas during treatment a significant female bias was evident in not only the first egg, but also in the second egg. The absence of single-egg clutches, the rarity of infertile eggs and the lack of laying delays between eggs strongly suggests that the mechanism of sex ratio adjustment in pigeons occurs prior to ovulation. The highly skewed sex-distribution within the two-egg clutches and the unexpectedly large amount of variation in the yolk weight of eggs produced during treatment (but not control) are consistent with the expectations of pre-ovulatory selective resorption of wrong sex ovarian follicles.     

不同海岸梯度上短枝木麻黄小枝金属元素含量及其再吸收率动态

对福建东山赤山林场不同海岸梯度上短枝木麻黄小枝中的钾(K)、钙(Ca)、镁(Mg)、钠(Na)、铁(Fe)、锰(Mn)和锌(Zn)元素含量及其再吸收率动态进行了研究.结果表明,海岸梯度对短枝木麻黄小枝中各元素含量及其再吸收率均具有显著影响.在各海岸梯度上,K再吸收率为正值,且基干林带的再吸收率显著低于其它样地,Fe和Zn为负值,Ca、Mg和Na再吸收率在防护林带前沿为负值,而在后沿林为正值,Mn则相反.这表明,基干林带严重的环境胁迫显著降低了短枝木麻黄小枝的养分再吸收率.短枝木麻黄成熟小枝中的K、Mg含量与其再吸收率存在显著正相关,而Na和Fe与其再吸收率存在显著负相关,其它元素与其再吸收率之间没有显著相关性.除K外,各元素在衰老小枝中的含量与相应元素再吸收率之间均存在显著负相关,表明元素再吸收程度越高,其再吸收率就越高.Ca、Mg、Na和Fe再吸收率之间具有显著的正相关关系(P<0.01),Zn除与Mn再吸收率呈显著正相关外,与其它元素均表现为负相关,Mn则与其它元素再吸收率之间没有显著相关性.因而短枝木麻黄小枝中不同类型的养分状况对其再吸收率具有不同的影响.表5参42     

黄土高原子午岭林区主要林分生态化学计量学特征

论文以黄土高原子午岭林区4种林分（侧柏、油松、辽东栎、刺槐）的绿叶、凋落物（凋落叶、枯枝、果实）为研究对象,分析其C、N、P含量及化学计量学特征,并计算养分再吸收率,为黄土高原植被恢复建设及人工林合理种植规划提供理论依据。结果显示：植物叶片凋落前N、P均发生营养转移,油松N养分再吸收率最高（44.73%）,刺槐P养分再吸收率最高（41.10%）;刺槐相比于其他3种林分,绿叶C含量（413.94 g·kg^-1）略低,且其4个组分N含量略高于其他林分的相应组分,绿叶、果实P含量相对较高;4种林分的枯枝C∶N、C∶P值最大,碳蓄积功能较强;叶片N∶P值均小于14,表明生长旺盛期林分主要受N限制。油松、刺槐养分再吸收能力强,是黄土高原森林区适宜植被恢复的造林树种。     

两种介孔分子筛动态吸附VOCs的研究

采用模板剂法制备了孔道规整、大比表面积的2种介孔分子筛MCM-41和SBA-15,并以甲苯、二甲苯、三甲苯为吸附对象,考察了介孔分子筛动态吸附VOCs的性能.结果表明,增加VOCs分子尺寸和浓度,降低床层温度可大幅提高介孔分子筛吸附性能.SBA-15由于介孔壁上的微孔结构适合吸附低浓度、小分子VOCs;MCM-41更适合吸附高浓度、大分子VOCs.TPD脱附试验表明,VOCs在介孔材料表面150℃下就能基本脱附完全.     

凉水和宝天曼地区乔木叶片氮素再吸收过程中δ15N的变化

植物自然丰度的稳定性N同位素(δ15N)在植物N吸收和N转运过程中会发生变化,但植物叶片在凋落之前的N素的再吸收如何影响δ15N变化还不清楚.本研究以凉水地区的14个常见树种和宝天曼地区的16个常见树种为研究对象,测定各树种新鲜叶和凋落叶及其对应土壤中的C、N质量分数和δ15N值.结果表明,凉水树种新鲜叶N质量分数和δ15N值显著高于宝天曼树种,这与凉水土壤的N质量分数和δ15N值都高于宝天曼土壤相对应.此外,凉水树种叶片N吸收率(47%)与宝天曼树种(40%)无显著差异.宝天曼树种凋落叶中的δ15N显著高于新鲜叶中的δ15N值,即叶片N再吸收过程中存在N同位素的分馏效应,而凉水树种凋落叶与新鲜叶中的δ15N无显著性差异.本研究首次报道在植物叶片N再吸收过程中存在显著的同位素分馏效应,而且分馏效应的程度与N再吸收率显著负相关.此外,植物叶片N再吸收过程中是否存在同位素分馏效应可能取决于叶片的N再吸收率;乔木新鲜叶片N质量分数和δ15N值在地区间的差异可能取决于土壤N质量分数和δ15N值的地区差异;叶片N再吸收率可能与N在叶片中的存在形态有关,而与土壤N质量分数不相关.     

The complexity of nectar: secretion and resorption dynamically regulate nectar features

In this paper, we review the phenomenon of nectar resorption, focusing on its physiological and ecological meaning. Nectar resorption is a phenomenon that has long been known but was rarely reported until the1990s. It has more recently been demonstrated in several species by various direct and indirect methodologies. It has generally been demonstrated in senescent flowers as a phenomenon separate in time from, and independent of, nectar secretion. The significance of this type of resorption is generally recognized as a resource-recovery strategy, recycling at least some materials invested in nectar production. Nevertheless, nectar resorption can occur concomitantly with nectar secretion. Nectar production is therefore best considered as a unified process comprising nectar secretion and resorption. The modulation of these two opposite phases allows nectar concentration to be maintained in a range suitable for pollinators (nectar homeostasis). The mechanism of nectar resorption at the cell level has received little attention, and its molecular basis can only be hypothesized on the basis of recent studies concerning sugar sensing.