Evolution in Dryopteris: The Role of Hybrids in Polyploid Speciation

不同物种之间的杂交是一种偶然现象， 在某些情况下可能会产生非常重要的结果： 新物种的起源 混合动力车通常无法 通过普通的性方式繁殖，因为它们含有 在减数分裂期间不配对的不相容染色体， 减数分裂产生单倍体细胞， 产生卵子和精子。 然而，第二个意外，染色体 加倍（多倍性）可以通过提供每个 有一个可以配对的完全相同的染色体。这些 两个过程，杂交和多倍性，结合在一起， 一种产生大量新植物物种的方法， 异源多倍体 异源多倍体包括了一些我们最重要的 农作物，其中包括小麦、棉花、咖啡、花生和烟草。 尽管如此，令人惊讶的是， 产生异源多倍体的细胞机制，或 当成功的时候， 异源多倍体形成。 本建议旨在加强我们对以下问题的认识： 异源多倍体的起源，通过详细的研究自然 鳞毛蕨属（Dryopteris）物种之间的杂交，鳞毛蕨属是一种常见的蕨类植物 北美洲东部 鳞毛蕨是一个理想的模式系统， （1）作为蕨类植物， 鳞毛蕨是孢子，可以直接生长成植物， 开花植物的花粉粒或胚囊， 更不适合进一步研究;（2）鳞毛蕨属植物大 并产生大量的孢子， 观察到相对罕见的事件;（3）许多杂交种产生于 自然，其中一些非常频繁，允许变化 在属于各种杂交种的过程之间， 评估。 本研究将包括两个阶段，实验室阶段和 一个实地阶段。 在实验室中， 将遵循双染色体。 这种孢子被认为是 可以被区分为大的球形（“巨型”）孢子， 从通常产生的枯萎孢子中分离出来 混合动力车 遗传组成和生长潜力 这些“巨型”孢子将通过将它们培养成 幼年蕨类植物（配子体），并使用分子生物学技术 和显微技术。 还将尝试生产 成年蕨类植物（孢子体）从配子体通过有性和 无性的手段。 在该领域，将研究杂交种的集群 以确定它们是否真的通过 多倍体孢子，即杂种是否都是第一个 一代，或包括一些后代。 分子 将使用指纹识别技术， 这两种可能性。 从这些组合场和 实验室研究将提供重要的新信息 杂种可以产生异源多倍体物种的手段。

Hybridization between different species is an accident of nature that may in some instances have a very important outcome: the origin of new species. Hybrids are typically unable to reproduce through ordinary sexual means because they contain incompatible chromosomes that do not pair during meiosis, the reduction division that produces the haploid cells that ultimately produce eggs and sperms. However, a second accident, chromosome doubling (polyploidy) may restore fertility by providing each chromosome with an exact duplicate with which it can pair. These two processes, hybridization and polyploidy, have combined in this way to produce a vast number of new plant species, termed allopolyploids. Allopolyploids include some of our most important crops, among them wheat, cotton, coffee, peanut, and tobacco. Nonetheless, surprisingly little is known about the precise cellular mechanisms that operate to produce allopolyploids, or about the circumstances that prevail in nature when successful allopolyploids become established. The present proposal is designed to bolster our knowledge of the origin of allopolyploids through detailed studies of natural hybrids between species of Dryopteris, a genus of ferns common in eastern North America. Dryopteris is an ideal model system for the following reasons: (1) as a fern, the products of meiosis in Dryopteris are spores that can be grown directly into plants rather than the pollen grains or embryo sacs of flowering plants which are much less amenable to further study; (2) Dryopteris plants are large and produce numerous spores, offering an enhanced opportunity to observe relatively rare events; (3) numerous hybrids are produce in nature, some of them very frequently, allowing for the variation between processes that pertain to individual kinds of hybrids to be evaluated. This study will consist of two phases, a laboratory phase and a field phase. In the laboratory, the production of spores with doubled chromosomes will be followed. Such spores are believed to be distinguishable as large spherical ("giant") spores that stand out from the remainder of the shriveled spores ordinarily produced by the hybrid. The genetic constitution and growth potential of these "giant" spores will be evaluated by growing them into juvenile ferns (gametophytes) and examining these using molecular and microscopic techniques. Attempts will also be made to produce adult ferns (sporophytes) from the gametophytes by both sexual and asexual means. In the field, clusters of hybrids will be studied to determine whether they are actually reproducing through polyploid spores, i.e. whether the hybrids are all first generation, or include some later generations. Molecular fingerprinting techniques will be used that can distinguish between these two possibilities. The results from these combined field and laboratory studies will provide important new information on the means by which hybrids can give rise to allopolyploid species.