Molecular Genetics of Pre-Mating Reproductive Isolation in Mimulus

在加利福尼亚的内华达山脉中部，有两种猴花，Mimulus lewisii和M. cardinalis，它们由不同的动物授粉——M. louisii由大黄蜂授粉，而M. cardinalis由蜂鸟授粉。为了吸引合适的传粉者，每一种Mimulus的花在颜色、大小、形状和花蜜产量上都有所不同。由于传粉者不同，这两种猴花在自然界中不能杂交，但通过人工授粉可以很容易地产生人工杂交。杂交品种的后代表现出巨大的花性状多样性，因为每个后代都从蜜蜂授粉的祖先那里继承了一部分基因组，从蜂鸟授粉的祖先那里继承了一部分基因组。没有两个杂交后代是完全相同的。200多只杂交后代将被带到加利福尼亚州的约塞米蒂国家公园，在那里，路易斯红雀和红雀一起被自然发现，大黄蜂和蜂鸟的到访率通过直接观察来测量。新的基因组测绘技术最初是为研究人类疾病和动植物育种而开发的，将用于确定花中的哪些基因负责吸引大黄蜂和蜂鸟。工作的假设是，一些基因，比如那些控制花朵颜色和花蜜生产的基因，将对传粉者选择访问特定的花朵有很大的影响。研究物种形成的遗传学——一个物种分裂成两个或两个以上新物种的过程——是理解生物多样性起源的基础。物种形成源于阻止两个物种杂交的基因变化。自达尔文以来，关于物种形成所需的基因变化的数量和大小一直存在争论。一种观点认为，生殖隔离是许多突变的累积结果，每个突变在很长一段时间内都有很小的影响。另一些人则认为，少数影响较大的基因起着突出的作用，物种形成可能会迅速发生。这个问题还没有解决，很大程度上是因为详细的基因研究仅限于少数生物，比如果蝇，它们作为实验模型已经有很长的历史了。基因组研究方法的改进使利用野生猴花物种建立现代实验室分子生物学与野外生态学研究的综合成为可能。这种一般的方法可以用来解决生物学中许多长期存在的问题。

9616522 Bradshaw In the central Sierra Nevada mountains of California there are two monkeyflower species, Mimulus lewisii and M. cardinalis, which are pollinated by different animals -- M. lewisii is bumblebee-pollinated, while M. cardinalis is pollinated by hummingbirds. The flowers of each Mimulus species differ in color, size, shape, and nectar production to best attract the appropriate pollinator. The two monkeyflower species do not crossbreed in nature because of their different pollinators, but artificial hybrids can be produced easily by hand-pollination. Offspring from the hybrids display a tremendous variety of floral traits, since each offspring has inherited part of its genome from a bee-pollinated ancestor and part from a hummingbird-pollinated ancestor. No two hybrid offspring are exactly alike. More than 200 hybrid offspring will be taken to Yosemite National Park in California, where M. lewisii and M. cardinalis are found together naturally, and the rates of bumblebee and hummingbird visitation measured by direct observation. New genome mapping techniques, originally developed for studying human disease and for plant and animal breeding, will be used to determine which genes in the flowers are responsible for attracting bumblebees and hummingbirds. The working hypothesis is that a few genes, such as those governing flower color and nectar production, will have a large impact on which pollinator chooses to visit a particular flower. Investigating the genetics of speciation -- the process by which one species splits into two or more new species -- is fundamental to understanding the origin of biodiversity. Speciation results from genetic changes that prevent the two species from crossbreeding. Since Darwin, there has been debate about the number and magnitude of genetic changes required for speciation. One view is that reproductive isolation is the cumulative result of many mutations, each with a small effect, over long periods of time. Alternatively, others have suggested that a few genes of large effect play a prominent role, and that speciation could occur rapidly. This issue has not been resolved, largely because detailed genetic studies have been limited to a few organisms, such as fruit flies, which have a long history as experimental models. Improved methods in genome research make it feasible to use wild monkeyflower species to establish a synthesis of modern laboratory molecular biology with ecological studies in the field. This general approach could be used to address many long-standing questions in biology.