Shykoff Jacqui A, Bucheli Erika, Kaltz Oliver
Experimental Ecology, Swiss Federal Institute of Technology, ETHZ-NW, 8092, Zürich, Switzerland.
Evolution. 1997 Apr;51(2):383-392. doi: 10.1111/j.1558-5646.1997.tb02425.x.
Mating opportunities, pollination intensity, and pollen dispersal ability may vary with variation in floral traits such as color, size, and shape. Where these traits are selected by pollinators for enhanced elaboration, they should evolve toward the equilibrium between selection for further elaboration and selection against this through reduced fecundity or vitality. Here we show that pollinator-borne fungal diseases of plants may be a factor influencing the position of this equilibrium. Populations of the rock pink, Dianthus silvester often contain individuals infected with the anther smut fungus Microbotryum violaceum (= Ustilago violacea). In a naturally infected population in the Alps of eastern Switzerland we investigated how intrapopulation variation in flower size and nectar rewards influenced spore deposition and how floral traits varied with disease status. We found that spore deposition increased with increasing petal size, suggesting that large-flowered plants were at a greater risk of disease. Spore deposition was also higher for plants growing in patches with many or a high proportion of diseased neighbors. Multiple regression analyses showed that petal size or nectar reward influenced spore deposition when the effects of neighborhood disease abundance were controlled statistically. In sequential analyses, after removing the effects of disease density or frequency and plant gender, petal length explained significant variation in spore deposition. Diseased plants had reduced female reproductive organs, but calyx size was intermediate between that of healthy perfect and female flowers of this gynodioecious-gynomonoecious species, and diseased plants bore flowers with the largest petals. This may reflect a symptom of this disease or the cause, if larger-flowered plants are more likely to become infected. We conclude that investment to pollinator attraction may bring an enhanced risk of contracting this sterilizing pollinator-borne disease, so natural selection by the fungus M. violaceum acts to lower attractiveness to pollinators.
交配机会、授粉强度和花粉传播能力可能会随着花朵特征（如颜色、大小和形状）的变化而变化。当传粉者选择这些特征以促进其进化时，它们应朝着进一步进化的选择与因繁殖力或活力降低而产生的反向选择之间的平衡方向发展。在这里，我们表明植物的传粉者传播的真菌疾病可能是影响这种平衡位置的一个因素。岩生石竹（Dianthus silvester）种群中常常有感染花药黑粉菌（Microbotryum violaceum = Ustilago violacea）的个体。在瑞士东部阿尔卑斯山的一个自然感染种群中，我们研究了种群内花朵大小和花蜜回报的变化如何影响孢子沉积，以及花朵特征如何随疾病状况而变化。我们发现孢子沉积随着花瓣大小的增加而增加，这表明大花植物感染疾病的风险更大。生长在有许多患病邻居或患病邻居比例较高的斑块中的植物，其孢子沉积也更高。多元回归分析表明，在对邻域疾病丰度的影响进行统计控制后，花瓣大小或花蜜回报会影响孢子沉积。在顺序分析中，去除疾病密度或频率以及植物性别的影响后，花瓣长度解释了孢子沉积的显著变化。患病植物的雌性生殖器官减少，但萼片大小介于该雌雄异株 - 雌雄同株物种的健康完全花和雌花之间，并且患病植物的花朵花瓣最大。这可能反映了这种疾病的症状或病因，如果大花植物更有可能被感染的话。我们得出结论，对传粉者吸引力的投入可能会增加感染这种由传粉者传播的绝育疾病的风险，因此紫罗兰色微座孢菌的自然选择作用是降低对传粉者的吸引力。
