Peakall Rod, Handel Steven N
School of Biological Sciences, Macquarie University, NSW, 2109, Australia.
Department of Biological Sciences, Rutgers University, Piscataway, New Jersey, 08855-1059.
Evolution. 1993 Dec;47(6):1681-1687. doi: 10.1111/j.1558-5646.1993.tb01260.x.
Pollinators have influenced the evolution of many morphological floral traits, although few studies have shown that pollinators have influenced plant height. Chiloglottis trilabra is one of many Australian orchids that deceive and attract male pollinators by mimicking the sex pheromones and morphology of females insects. Orchids in this genus have unusually short flowers whose peduncle elongates dramatically after pollination to approximately twice the original height. In a series of choice experiments in the field, we show that pollinators of C. trilabra strongly discriminate among floral heights, preferring flowers presented at 15 cm-20 cm over flowers presented at lower and higher positions (ranging from 2 cm-100 cm). Our results suggested pollinators have the potential to mediate stabilizing selection for floral height when pollination is limiting. However, the natural height range of the orchid (mean = 10 cm, range 5 cm-15 cm) was lower than the experimentally determined optimum for visitation frequency. This difference may indicate that pollinator-mediated selection does not occur in this species, perhaps because seed set is not sufficiently limited. Alternatively, other life-history factors may counteract pollinator-mediated selection, yielding an evolutionary compromise in height.
传粉者影响了许多花部形态特征的进化，不过很少有研究表明传粉者会影响植株高度。三裂指柱兰是澳大利亚众多兰花之一，它通过模仿雌性昆虫的性信息素和形态来欺骗并吸引雄性传粉者。该属兰花的花朵异常短小，其花梗在授粉后会急剧伸长至原来高度的约两倍。在一系列田间选择实验中，我们发现三裂指柱兰的传粉者对花的高度有强烈的偏好，相较于处于较低和较高位置（2厘米至100厘米）的花朵，它们更喜欢高度在15厘米至20厘米的花朵。我们的结果表明，当授粉受限的时候，传粉者有可能对花的高度进行稳定选择。然而，这种兰花的自然高度范围（平均10厘米，范围5厘米至15厘米）低于实验确定的最佳访花频率高度。这种差异可能表明该物种中不存在传粉者介导的选择，也许是因为结实率没有受到足够的限制。或者，其他生活史因素可能会抵消传粉者介导的选择，从而在高度上产生进化妥协。
