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首页> 外文学位 >Intrapopulation sex ratio variation and sexual specialization in the dioecious grass Distichlis spicata.
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Intrapopulation sex ratio variation and sexual specialization in the dioecious grass Distichlis spicata.

机译：雌雄异株Distichlis spicata的种群内性别比变异和性专长。

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Within-population sex ratio variation along an environmental gradient---a pattern labeled spatial segregation of the sexes---is an extreme form of sex ratio bias commonly found in dioecious plants. Spatial segregation of male and female individuals is surprising in an immobile organism because limited dispersal of gametes should reduce sexual reproductive success, and presumably fitness, of individuals. Little is known about the ecological and evolutionary mechanisms responsible for this pattern.; In California populations of the clonal, perennial grass Distichlis spicata, I examined sex ratio variation along micro-elevation gradients correlated with soil fertility and tidal inundation. First, using RAPD markers, I demonstrated that this species exhibits spatial segregation of male and female genets, rather than simply segregation of ramets or flowering potential, and that sex is genetically determined. Second, although gender-specific juvenile mortality has rarely been examined in plants, I used RAPD markers to identify the sex of seedlings and thereby determine whether differential seed germination and seedling mortality are proximate mechanisms for spatial segregation of the sexes in this species. In majority-female habitats, gender-specific bias in seedling survivorship and seed germination do occur, but only variation in seedling survivorship helps explain the observed sex ratio bias. Third, I examined whether specialization of the sexes to different microhabitats occurs in D. spicata, a scenario not previously shown for a dioecious plant species. I determined that microhabitats differentially affect flowering in the sexes. Moreover, female seedlings have a greater suppressive effect on neighbors than do male seedlings, a finding that supports speculation that females competitively exclude males from high-quality habitats. Fourth, by examining pollen movement and the effects of pollen load, nutrient availability, and male ramet densities on seed set, I found that spatial segregation of the sexes in this species limits the mating success of males and females. These data are the first of their kind, and they give the most comprehensive picture of the causal mechanisms for, and consequences of, spatial segregation of the sexes in any plant species. Data of this kind are essential for evaluating hypotheses concerning the evolution of sexual segregation and dioecy.
机译：沿环境梯度的种群内性别比变化-一种标记为性别空间隔离的模式-是雌雄异株植物中常见的性别比偏差的一种极端形式。在不活动的生物中，男性和女性个体的空间隔离是令人惊讶的，因为配子的有限扩散会降低个体的性生殖成功率，并可能降低其适应性。对导致这种模式的生态和进化机制知之甚少。在加利福尼亚多年生无性系Distichlis spicata的无性系种群中，我研究了沿着微高梯度的性别比变化，该梯度与土壤肥力和潮汐淹没有关。首先，我使用RAPD标记证明该物种表现出男性和女性种系的空间隔离，而不仅仅是分株或开花潜能的隔离，并且性别是由基因决定的。其次，尽管很少在植物中检查过针对性别的少年死亡率，但我使用RAPD标记物来识别幼苗的性别，从而确定差异的种子萌发和幼苗死亡率是否是该物种中性别空间隔离的最接近机制。在多数雌性生境中，确实会出现性别差异对幼苗存活率和种子萌发的影响，但是只有幼苗存活率的变化有助于解释观察到的性别比偏差。第三，我检查了D. spicata中是否发生了将性别专门化为不同的微生境的情况，这种情况以前并未显示为雌雄异株的物种。我确定微生境对性别的开花有不同的影响。此外，雌性幼苗比雄性幼苗对邻居的抑制作用更大，这一发现支持了推测，即雌性竞争性地将雄性排除在优质栖息地之外。第四，通过研究花粉运动以及花粉负载，养分利用率和雄性分株密度对结实的影响，我发现该物种性别的空间隔离限制了雄性和雌性的交配成功。这些数据尚属首次，它们最全面地描绘了任何植物物种中性别空间隔离的原因机制及其后果。此类数据对于评估有关性别隔离和两性关系演变的假设至关重要。

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