Faculty of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan.
J Theor Biol. 2010 May 21;264(2):223-36. doi: 10.1016/j.jtbi.2010.01.030. Epub 2010 Feb 2.
Masting is synchronous intermittent production of seeds in perennial plant populations. Some self-compatible monoecious Quercus species, such as oaks, exhibit sex ratio dimorphism and produce a certain proportion of male flowers, even in a year when no seed set occurs. To investigate sex ratio dimorphism in masting trees, we introduced sexual allocation as an evolutionary trait into the Resource Budget Model and examined the evolution of the sex ratio. Analytical and numerical findings show that (1) perfectly synchronous intermittent reproduction does not evolve; (2) if the fruiting cost of female flowers R(c) is sufficiently large and the pollen limitation beta is intermediate, annual reproduction does not evolve; (3) under conditions (2), sex ratio dimorphism can evolve across a wide region of parameter space; (4) after dimorphism is established, individuals with a female-biased sex ratio receive much more pollen supply from male-biased individuals and tend to show intermittent reproduction with or without synchrony; and (5) dimorphism is maintained with irregular and nearly discontinuous changes of sex ratio. These results suggest that sex ratio dimorphism contributes to improving pollen availability and causes resource depletion and the occurrence of intermittent reproduction in female-biased individuals.
结实朿性是多年生植物种群中同步的间歇性种子生产。一些自交雌雄同体的栎属物种，如橡树，表现出性别二态性，并产生一定比例的雄花，即使在当年没有种子形成的情况下也是如此。为了研究结实朿性树木的性别二态性，我们将性资源分配作为一个进化特征引入资源预算模型，并研究了性别比的进化。分析和数值结果表明：(1)完全同步的间歇性繁殖不会进化；(2)如果雌花的结实成本 R(c)足够大，花粉限制β处于中间水平，那么年度繁殖就不会进化；(3)在条件(2)下，性别二态性可以在参数空间的广泛区域进化；(4)在建立二态性之后，具有雌性偏性性别比的个体从雄性偏性个体获得更多的花粉供应，并倾向于表现出有或没有同步性的间歇性繁殖；(5)二态性通过性别比的不规则且几乎不连续的变化得以维持。这些结果表明，性别二态性有助于提高花粉的可用性，并导致雌性偏性个体中资源枯竭和间歇性繁殖的发生。
