隔离机制和隔离机制 -- -- 高级

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How did the mouse cross the river?
::老鼠是怎么过河的?

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Chances are, with a river like this, it didn't. If a of mice becomes divided into two as a river forms or some other geographic division occurs, will that population eventually become two distinct populations and two separate ?
::如果小鼠以河流的形式被分为两种,或者出现其他地理划分,人口最终会变成两个不同的人口和两个不同的人口吗?

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Isolating Mechanisms
::隔离机制

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Biologists today divide isolating mechanisms into two major categories based on whether they happen in different locations ( allopatric = “other fatherland”) or a single location ( sympatric = “same fatherland”) ( Figure  ).
::今天,生物学家将孤立机制分为两大类,主要根据是发生在不同地点(异父系或“其他祖国”)还是发生在单一地点(同父系或“同父系”)(图)。

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Allopatric Speciation
::国与国间团结

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Allopatric speciation involves geographic barriers, which physically isolate populations. Formation of a land bridge such as the Isthmus of Panama, for example, could separate members of a population into two groups. Emergence of a mountain range could separate members of a lowland species. According to the , the rifting of continents divided populations of and plants. In these cases, dramatic changes in landforms lead to geographic isolation; however, movements of animals and plants can also result in physical isolation. Single individuals or small groups of individuals may move away from a parent population to colonize a new area, and the new colony could be isolated from its parent population. Such movements are not always intentional; a storm apparently carried a small flock of finches from the coast of South America to the Galapagos Islands. In each case, geographic barriers (the land bridge, the ocean) isolate the two populations so that stops and genetic divergence can proceed. may lead each population to adapt to its own unique environment, or may lead to chance differences in gene pools. If genetic divergence results in reproductive incompatibility, the two populations have become two separate species.
::例如,巴拿马地峡等陆地桥梁的形成可以将人口分为两个群体; 山脉的出现可以将低地物种成员分开; 根据各大洲的分裂,各大洲的人口和植物的分裂; 在这些情况下,土地形态的急剧变化导致地理孤立; 然而,动物和植物的移动也可能导致实际隔离; 单个个人或小群个人可能离开母人口,进入新地区殖民,而新的殖民地可能与其母人口隔离; 这种移动并非始终是有意的; 一场风暴显然将一小群小群鳍从南美洲海岸到加拉帕戈斯群岛; 在每一种情况下,地理屏障(陆地桥梁、海洋)将两个人口隔离,从而导致停止和遗传差异的发生; 可能导致每个人口适应自己独特的环境,或可能导致基因群的偶然差异; 如果遗传差异导致生殖不相容,两个种群就变成两个单独的物种。

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Diane Dodd, working with a population of fruit flies ( Figure ), experimentally verified the idea that physical isolation can lead to reproductive isolation and . Dodd split the population into two groups, and fed maltose to one group and starch to the other. She observed that each new environment selected for improved efficiency in digesting the available food molecule. After eight or more generations of isolation, the two populations were recombined. After isolation, “starch” flies preferred to mate with other “starch” flies, and “maltose” flies preferred “maltose” mates. Although the preferences were not absolute, they did demonstrate at least initial formation of a reproductive barrier.
::Diane Dodd与一群果蝇一起工作(图 ) , 实验性地验证了身体隔离可能导致生殖隔离的想法。 Dodd将人口分为两个组,向一个组和另一个组喂麦芽,向另一个组提供淀粉。她指出,为了提高消化现有食物分子的效率而选择的每一种新环境,经过八代或八代以上的隔绝后,这两个组群重新组合。在隔绝后,“starch”苍蝇更愿意与其他“starch”苍蝇交配,“maltose”苍蝇更喜欢“maltose”伴侣。 虽然偏好不是绝对的,但至少显示了最初形成的生殖屏障。

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Sympatric Speciation
::血后血后血后血后血 血后血后血后 血后血后血后血后血后

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Sympatric speciation involves the emergence of a new species within the geographic range of the parent population. In the absence of geographic isolation, reproductive barriers must arise in different ways in order for new species to form. Some biologists doubt the relative importance of sympatric speciation to evolutionary change, but several examples demonstrate the potential for this mechanism of evolution.
::血缘特征是指在母系人口的地理范围内出现一种新的物种,在没有地理隔离的情况下,生殖障碍必须以不同的方式出现,以便形成新的物种。 一些生物学家怀疑血缘特征对于进化变化的相对重要性,但有几个例子表明这种进化机制的潜力。

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The following example shows one-way sympatric speciation can occur:
::以下例子显示了单向的血缘特征:

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1. Hawthorn flies lay eggs in hawthorn trees (see Figure  ). The eggs hatch into larvae that feed on hawthorn fruits. Both the flies and trees are native to the U.S.
   ::Hawthorn苍蝇在Hawthorn树上产卵(见图 ) 。 这些蛋孵化成以Hawthorn水果为食的幼虫。 这些苍蝇和树都是美国本土的。
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2. Apple trees were introduced to the U.S. and often grow near hawthorn trees. Some hawthorn flies started to lay eggs in nearby apple trees. When the eggs hatched, the larvae fed on apples.
   ::苹果树被引入美国,并常常在哈霍恩树附近生长。 一些哈霍恩苍蝇开始在附近的苹果树上产卵。 当蛋孵化时,幼虫靠苹果喂养。
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3. Over time, the two fly populations—those that fed on hawthorn trees and those that preferred apple trees—evolved reproductive isolation. Now they are reproductively isolated because they breed at different times. Their breeding season matches the season when the apple or hawthorn fruits mature.
   ::随着时间推移,两种苍蝇——即那些靠长角树为食的苍蝇和那些偏爱苹果树的苍蝇——在生殖上与世隔绝,现在它们由于在不同的时间繁殖而处于生殖上的孤立状态,它们的繁殖季节与苹果或长角水果成熟的季节相匹配。
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4. Because they rarely interbreed, the two populations of flies are evolving other genetic differences. They appear to be in the process of becoming separate species.
   ::这两组苍蝇很少相互交织,因此正在演变其他基因差异。 它们似乎正在成为独立的物种。

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Polyploidy
::聚球体

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In plants, new species occasionally arise by duplication of – a condition known as polyploidy ( Figure  ). Recall that our are diploid and that egg and cells are haploid . If fails to reduce the number of chromosomes, diploid sex cells result. In plants, which can self-pollinate , diploid pollen may fertilize a diploid egg, resulting in a tetraploid offspring. Although tetraploids may self-pollinate or interbreed with other tetraploids, they cannot successfully reproduce with their parents, because three sets of chromosomes (two from the tetraploid parent and one from the “normal” diploid parent) cannot successfully perform the intricate dance of meiosis. Peanuts, potatoes, and cotton are familiar crops that are tetraploid. Strawberries and sugarcane are octaploid (eight sets of chromosomes in each cell, compared to our two). Polyploidy is a common form of speciation in plants in nature, as well as in .
::在植物中,新物种偶尔会因重复而出现 — — 一种被称为聚虫(Figre ) 的状态。 回顾我们是低脂的,蛋和细胞是顺质的。如果不能减少染色体的数量,低脂的性细胞就会产生这种结果。在可以自我污染的植物中,低脂的花粉可能会对浸泡蛋施肥,从而产生一种四质的后代。尽管四酚可能会自我污染,或者与其他四质体(Figre ) 发生接触,但它们无法成功地与父母繁殖,因为三组染色体(两组来自四质的母体,另一组来自“正常”的母体 )无法成功地进行复杂的蜜质病舞蹈。 花生、土豆和棉花是常见的作物,都是四质的。 草莓和甘蔗是八色(每组有八组的染色体,而我们两个细胞有八组 ) 。 多质类是自然植物中常见的特征形式。

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Two species of plants may hybridize – often forming unusually vigorous hybrid offspring. Unfortunately, despite their vigor, these offspring are often infertile due to chromosome incompatibility. However, if polyploidy occurs within the offspring, each of the previously unmatched chromosomes has a partner, offspring fertility is restored, and a new species is formed. Triticale ( Figure ), a hexaploid hybrid of wheat and rye, was produced in the laboratory in this manner. Combining the high yield and quality of wheat with the disease-resistance of rye, triticale is now a successful grain crop in Europe, China, and Australia.
::两种植物可能混合 — — 通常形成异常活跃的混合后代。 不幸的是,尽管这些后代有活力,但由于染色体不相容,它们往往不育。 但是,如果多溴性在后代中出现,每个以前不相配的染色体都有伴侣,后代生育力得到恢复,新物种也形成。 以这种方式在实验室生产了三丁基(Figore ) , 即小麦和黑麦的六溴混合体。 将小麦的高产量和质量与莱伊病抗体相结合,三丁香现在在欧洲、中国和澳大利亚是成功的谷物作物。

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Polyploidy is less common in animals, perhaps because they less frequently self-fertilize. Some are polyploid, but offspring are usually sterile and “species” reproduce by parthenogenesis ( from unfertilized eggs). Human and other mammalian livers often contain many polyploid cells.
::在动物中,多胞胎不太常见,或许是因为多胞胎的自肥频率较低。 有些是多胞胎,但后代通常是不育的,“物种”则由(未受精的卵子)分泌而来。 人类和其他哺乳动物肝脏通常含有许多多胞胎细胞。

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Although polyploidy is rare among animals, other zoological modes of sympatric speciation exist. For example, environmental change within a population’s range may lead to two habitats in which genetic divergence may take place. Our hypothetical rabbit example, discussed in the concepts, is an example of this type of sympatric speciation. A field example involves the hawthorn fly discussed above ( Figure  ), whose larval maggot stage feeds on hawthorn fruit. Apple trees, introduced to the US, often grow near hawthorns, and some hawthorn flies have begun to feed on apples. The two populations, although sympatric, have developed significant genetic differences and, at least in the wild, no longer tend to interbreed. This apparent reproductive isolation involves temporal divergence (apples and hawthorns and their respective fly populations mature in slightly different seasons) and mating and egg-laying preferences (linking larval fruit to adult behavior). Many biologists consider these flies to be an example of sympatric speciation in progress. This environmental complexity has led to speciation as distinct groups of what was once the same population occupy different niches.
::尽管动物中多栖类动物很少见,但其他动物的共产性物种模式也存在。例如,一个人口范围内的环境变化可能导致两个生境出现遗传差异。我们在概念中讨论的假设兔子例子就是这种类共产性物种的例子。一个实地的例子涉及上文讨论的长毛蜂苍蝇(Figure ) , 其幼虫蠕虫阶段养成长在果上。 引入美国的苹果树,常常在附近生长,而一些蝇开始食用苹果。 这两种动物,尽管是双栖类,但已经发展了巨大的遗传差异,至少在野外,不再倾向于相互交织。这种明显的生殖隔离涉及时间差异(在稍有不同季节成熟的鹦鹉和它们各自的苍蝇群 ) , 以及交配配和产卵偏好(将幼蝇与成年人行为联系起来 ) 。 许多生物学家认为这些苍蝇是种的典型例子,尽管是双栖类动物,但它们发展了显著的基因,至少在野外,也不再倾向于相互交织。 这种明显的环境差异性环境差异性群体曾经导致不同的背景。

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Cichlid in East Africa’s Lake Victoria illustrate both allopatric and sympatric speciation ( Figure  ). Less than a million years old, the Lake harbors nearly 200 closely related cichlid species. Biologists conclude that adaptive radiation by a small group of colonizers into available niches explains the diversity of feeding specializations among these closely related species, much like Darwin’s finches in the Galapagos. Because the various habitats in the huge Lake (or islands in the oceans) isolate populations, adaptive radiation is often considered a type of allopatric speciation. However, nonrandom mating may have led to at least one more recent sympatric speciation. Females of two closely related species appear to select mates based on differing, brightly colored backs. Although the two color variations can still interbreed in the lab, they do not appear to do so in nature.
::东非维多利亚湖的Cichlid在东非维多利亚湖(Figure ) , 既说明了异族和同族物种(Figure ) 。 不到一百万年,湖中藏有近200种紧密相连的异族物种。 生物学家得出结论,少数殖民者将适应性辐射植入到现有位置,这解释了这些密切相关的物种(与加拉帕戈斯达尔文在加拉帕戈斯的雀巢类似 ) ) 之间不同的养殖专业。 由于巨大的湖(或海洋中的岛屿)中的不同生境隔离了人口,适应性辐射往往被视为一种异族物种。 然而,非随机交配至少导致了至少一个最近的异族物种。 两个密切相关的物种中的女性似乎根据不同、明亮的背色选择了伴侣。 尽管两种不同颜色的变异在实验室中仍然可以相互交织,但他们似乎并没有这样做。

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Summary
::摘要

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• Allopatric speciation involves geographic barriers, which physically isolate populations.
  ::宗教种族分界涉及地理障碍,使人口在身体上隔离。
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• Barriers to mating and barriers to development of zygotes can both cause reproductive isolation.
  ::结交的障碍和发展zygotes的障碍都可能造成生殖隔离。
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• Experiments with fruit flies support the possibility that geographic isolation can lead to reproductive isolation.
  ::果蝇实验支持了地理隔离可能导致生殖隔离的可能性。
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• Sympatric speciation involves the emergence of a new species within the geographic range of the parent population.
  ::血缘特征是指在母系人口的地理范围内出现一种新的物种。
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• In plants, polyploidy is a common sympatric form of “instant speciation.”
  ::在植物中,聚脂类是一种常见的“即时分化”的共性形式。
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• Hybridization and polyploidy have formed many vigorous crop species.
  ::混合化和多花类已形成许多活跃的作物物种。
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• In animals, environmental complexity may lead to sympatric speciation.
  ::在动物中,环境的复杂性可能导致同父异母的分化。
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• Cichlid fish in Lake Victoria illustrate both adaptive radiation – a form of allopatric speciation – and more recent sympatric speciation due to heritable changes in mating preference.
  ::维多利亚湖的Cichlid鱼既说明了适应性辐射 — — 一种统包父系物种形式 — — ,也说明了最近由于亲子关系偏好的遗传性变化而出现的共包父系物种特征。

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Review
::回顾

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1. Distinguish allopatric from sympatric speciation.
   ::将同父异母的同父异母的区别开来
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2. Describe two examples of reproductive isolation.
   ::描述生殖隔离的两个例子。
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3. Describe the use of hybridization and polyploidy to form new crop species.
   ::说明如何使用混合和聚ploy来形成新的作物品种。
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4. Analyze the importance of environmental complexity to sympatric speciation for animals.
   ::分析环境复杂性对于动物的同父异母物种特征的重要性。