Taylor Douglas R, Trimble Steven, McCauley David E
Department of Biology, Gilmer Hall, University of Virginia, Charlottesville, Virginia, 22903.
Department of Biology, Denison University, Granville, Ohio, 45005.
Evolution. 1999 Jun;53(3):745-751. doi: 10.1111/j.1558-5646.1999.tb05368.x.
Recent theoretical models have addressed the influence of metapopulation dynamics on the fitness of females and hermaphrodites in gynodioecious plants. In particular, selection is thought to favor hermaphrodites during population establishment because that sex should be less prone to pollen limitation, especially if self-fertilization is possible. However, inbreeding depression could limit this advantage. In this experimental study of Silene vulgaris, a weedy gynodioecious plant, the fitness of females and hermaphrodites was estimated from seed production in both mixed-sex populations and for individuals isolated from these populations by 20, 40, 80, or 160 m. In mixed populations females display statistically significant greater per capita seed production owing to higher capsule production and higher rates of seed germination. The fitness of both sexes declines with increasing isolation, but at different rates, such that in the 160-m treatment hermaphrodites are by far the more fit sex. Allozyme studies suggest that this differential decline is because the selfing rate in hermaphrodites increases as a function of isolation, at least partially compensating for a decline in the availability of outcross pollen. Overall, the negative effects of pollen limitation on females far outweighs the negative effects of inbreeding depression following selfing in hermaphrodites. Thus, extinction/recolonization dynamics would appear to favor hermaphrodites as long as seed dispersal events exceed some critical distance.
最近的理论模型探讨了集合种群动态对雌雄异株植物中雌性和雌雄同体适合度的影响。具体而言，在种群建立过程中，选择似乎有利于雌雄同体，因为该性别应该较少受到花粉限制，特别是如果自花受精是可能的。然而，近亲繁殖衰退可能会限制这一优势。在对杂草性雌雄异株植物普通麦瓶草的这项实验研究中，通过混合性别种群以及从这些种群中分离20米、40米、80米或160米的个体的种子产量来估计雌性和雌雄同体的适合度。在混合种群中，由于更高的蒴果产量和更高的种子发芽率，雌性的人均种子产量在统计学上显著更高。两性的适合度都随着隔离距离的增加而下降，但下降速率不同，因此在160米处理中，雌雄同体是到目前为止更适合的性别。等位酶研究表明，这种差异下降是因为雌雄同体的自交率随着隔离距离的增加而增加，至少部分补偿了异交花粉可用性的下降。总体而言，花粉限制对雌性的负面影响远远超过雌雄同体自交后近亲繁殖衰退的负面影响。因此，只要种子传播事件超过某个临界距离，灭绝/再定殖动态似乎有利于雌雄同体。
