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

Aims The evolution and expression of dispersal-related traits are intertwined with those of other life-history functions and are manifested within various physiological constraints.Such a relationship is predicted between inbreeding levels and dispersability,which may be anatomically and ontogenetically linked so that the selection pressures on one may affect the other.While both the effect of inbreeding on reproductive success and on dispersal strategies received much attention,only a few studies considered both simultaneously.Furthermore,such studies often rely on two dichotomic representations of breeding and dispersal:using selfing versus outcrossing as a representation of breeding level,and dispersal ratio as the sole representation of dispersal strategy.Methods Here,we used pollination experiments in the heterocarpic Crepis sancta(Asteraceae)to expand in two different manners on the common practice of using dichotomic representations of breeding and dispersal.First,we used pollination treatments that represent a continuum from selfing through pollination by kin to pollination by a distant neighbor.Second,we measured a whole set of continuous morphological and dispersal-related traits,in addition to measurements of reproductive success and dispersal ratio.Important Findings The proportion of developed capitula and the number of both dispersed and non-dispersed achenes were significantly lower in the self-pollination treatment in comparison to the outcrossed treatments.The effect of pollen sources on dispersal ratio was not statistically significant,though self-pollinated plants rarely produced non-dispersing seeds.Achene's biomass increased with distance between parent plants,but pappus width did not,leading to a nonsignificant effect of pollination on falling velocity.Overall,pollen source affected mainly traits that were associated with reproductive output,but it had no clear effect on predominately dispersal-related traits.Such differences in the response of reproduction and dispersal traits to variation in pollen source suggest that dispersal-related selection is probably weak and/or masked by other forces.

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Qep/ssancta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。