Sánchez-Lafuente Alfonso M, Parra Raquel
Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 9, 41012 Sevilla, Spain.
Ann Bot. 2009 Sep;104(4):689-701. doi: 10.1093/aob/mcp140. Epub 2009 Jun 9.
The phenotypic selection of a diverse insect assemblage was studied on a generalist plant species (Paeonia broteroi) in ten flowering seasons, with tests for whether visitor preferences for plants with larger flowers eventually translated into significant differences among plants in visitation rates, seed production, seed mass, seed germination and seedling survival.
Selection gradients were used to assess if selection on flower size contributed to explain differences in visitation rates, seed production and seed mass. First, independent analyses were carried out for each season; then for the ten season as a whole. Seedling emergence and survival were assessed by generalized linear models.
Directional selection was found on flower size through visitation rates and seed production, and stabilizing selection through seed mass. Thus, larger flowers were more visited, and produced more, but lighter seeds, than smaller flowers. The results suggest a conflicting selection on flower size through seed number and size. Floral integration found in the study populations was larger than that in populations of a distant region. Finally, seed size did not influence seedling emergence and survival; thus, any advantages of seed size may be constrained under natural conditions before plants become reproductive individuals.
Plants with larger flowers may be benefited by producing more lighter seeds than fewer heavier ones, as they may contribute disproportionately to the seed bank, and have better chances that any descendant could eventually recruit. However, it seems unlikely that differences in flower size and integration found among populations in different regions could have been originated by rapid evolutionary change. First, because of the conflicting selection described; second, because of the remarkably low seedling survival found under natural conditions. Consequently, the influence of pollinator selection alone does not seem to explain differences in flower size and integration.
在十个开花季节里，对一种广布植物物种（阔叶芍药）上多样的昆虫群落进行了表型选择研究，测试访花者对较大花朵植物的偏好是否最终转化为不同植物在访花率、种子产量、种子质量、种子萌发和幼苗存活方面的显著差异。
利用选择梯度来评估对花大小的选择是否有助于解释访花率、种子产量和种子质量的差异。首先，对每个季节进行独立分析；然后对整个十个季节进行分析。通过广义线性模型评估幼苗出土和存活情况。
通过访花率和种子产量发现了对花大小的定向选择，通过种子质量发现了稳定选择。因此，较大的花朵比小花朵被访花的次数更多，产生的种子更多，但种子更轻。结果表明在种子数量和大小方面对花大小存在相互冲突的选择。研究种群中发现的花部整合大于遥远地区种群中的花部整合。最后，种子大小不影响幼苗出土和存活；因此，种子大小的任何优势在植物成为生殖个体之前的自然条件下可能会受到限制。
花朵较大的植物可能通过产生更多较轻的种子而非更少较重的种子而受益，因为它们可能对种子库有不成比例的贡献，并且任何后代最终成功定居的机会更大。然而，不同地区种群间发现的花大小和整合差异似乎不太可能是由快速进化变化引起的。首先，由于上述相互冲突的选择；其次，由于在自然条件下发现的幼苗存活率极低。因此，仅传粉者选择的影响似乎无法解释花大小和整合的差异。
