Prioritized contingencies: context-dependent regeneratory effects of grazer saliva

Naturally growing plants are able to plastically respond to myriad environmental challenges and opportunities. When confronted with multiple stresses, plants are expected to be able to prioritize their responses according to immediacy and predicted acuteness of these stresses. Here, we studied the interactive effects of competition and nutrient deprivation on growth responses of damaged Trifolium purpureum plants to salivary cues of a mammalian grazer. Salivary cues elicited marked growth responses in damaged but otherwise well-nourished and competition-free T. purpureum plants; however, this positive effect was annulled under Stipa capensis competition and was reversed under nutrient deficiency. The results suggest that the magnitude and direction of the effects of salivary cues on plant growth depend on an intricate prioritization of plant responses to prevailing and expected challenges and that T. purpureum plants perceive competition as a more acute stress than grazing. While herbivore saliva enables plants to reliably differentiate between herbivory and physical damage, the limited correlation between prevailing and future herbivory might reduce the informative value of salivary cues, rendering their effects weaker than those of prevalent competition and nutrient deficiency, whose continued detrimental effects are usually highly predictive. The results stress the importance of further studying the interactive effects of the acuteness and reliability of prevailing and anticipated stresses, and the informational content and adaptive value of environmental cues under various environmental circumstances.     

The effect of pollen source on seed traits and dispersability in the heterocarpic annual Crepis sancta

不同花粉来源对一年生植物种子性状和扩散能力的影响 与扩散有关的性状进化和表达与其他生活史功能交织在一起，并在各种生理约束条件下表现出 来。这种关系可以在近交水平和扩散性之间得到预测，而且在解剖学和个体发育上联系在一起，从而使 某个选择压力可能影响另外的一个。虽然近交对生殖成功和扩散策略的影响都引起了广泛关注，但只有 少数研究同时考虑了这两者。此外，此类研究通常依赖于繁殖和扩散的表示：使用自交与异源杂交表示繁殖水平，使用扩散比表示扩散策略。本研究利用菊科Crepis sancta的授粉实验，以两种不同的方式扩展 繁殖和扩散的二分表示法。首先，我们使用授粉处理来表示一种统一连续体，即从亲缘授粉的自交到距离较远的邻居授粉。其次，我们不仅测量了繁殖成功率和扩散比，还测量了一整套连续的与形态和扩散相关的性状。研究结果显示，头状花序的比例，以及扩散的和非扩散的瘦果在自花传粉处理中都显著低于异源杂交处理。尽管自花授粉的植物很少产生不扩散的种子，但花粉来源对扩散比的影响统计上不显著。瘦果的生物量随亲本植物之间的距离增加而增加，但冠毛宽度没有增加，从而导致授粉对下落速度的影响不显着。总之，花粉来源主要影响与生殖产量有关的性状，但对主要与扩散有关的性状没有显著影响。繁殖和扩散性状对花粉来源变化响应的这种差异表明，与扩散有关的选择可能很弱和/或被其他因素所掩盖。