死寂的沼泽地“死亡谷”目前仍是北美洲海拔最低、最干燥、最热的地区，其中生存着一种类似加拉帕戈斯群岛达尔文雀的沙漠鱼pupfish，人们可以观察到其进化的全过程，它正揭示着环境如何重塑着动物的体型和行为。
Pupfish的体型、大脑和行为都很灵活，其发育受早年环境的影响很大。这种灵活性称为表型可塑性，它对pupfish表型多样性的形成起着关键作用。许多动物如蜜蜂和脊椎动物都有表形可塑性。一些特殊表型的形成取决于他们特殊的栖息地，一旦栖息地变了，表型特征也会发生变化。死亡谷中的水温不适宜pupfish的生存繁衍，其中著名的“魔鬼洞”是pupfish唯一天然的栖息地。可塑性也是有遗传基础的，由生物个体的染色体组和生存环境共同决定。一个适应性进化的新方向取决于生物体本身是可变异的，这种变异共同取决于基因型和结构、生理、行为上的表型可塑性。
Pupfish的行为有赖于其栖息地的环境，而对唯一栖息地的过分依赖会使魔鬼洞的pupfish极易灭绝，为此人们建了三个模仿魔鬼洞环境的避难所。5年后发现，避难所中与魔鬼洞中的pupfish的表型差异很大，这正是环境差异使然。这些差异还包括攻击性和求爱行为的差异。对pupfish表型可塑性的探索日益紧迫，因为魔鬼洞从1990年开始就不明原因的在缩小。既然表现型由基因型和环境共同决定，因此，我们将如何努力保护特殊的基因和在特殊环境下生长的物种呢？ （陈仁杰/编译）
生物谷推荐英文原文：
The Phenotypic Plasticity of Death Valley's Pupfish
Desert fish are revealing how the environment alters development to modify body shape and behavior
Sean C. Lema
After a visit to Death Valley, the desert wanderer Edward Abbey wrote that "the first impression remains a just one. Despite variety, most of the surface of Death Valley is dead … a land of jagged salt pillars, crackling and tortured crusts of mud, sunburnt gravel bars the color of rust, rocks and boulders of metallic blue naked even of lichen." For the most part, that description is accurate. As one of the world's harshest desert regions, Death Valley is a land of eroding badlands, scorching alluvial fans, and barren flats of mud and salt.
Even maps of the Death Valley region of California and Nevada allude to the region's sweltering temperatures. Furnace Creek, the Funeral Mountains, Dante's View, the Devil's Golf Course—the names of its geological features are omens of an extreme landscape. And, in those extremes, Death Valley delivers. Death Valley holds concurrent titles of being the lowest, driest and hottest location in North America. The valley's floor dips 86 meters below sea level and is the lowest location in the Western Hemisphere. In an average year, Death Valley receives only 5 centimeters of precipitation, and temperatures soar routinely above 49 degrees Celsius during summer.
Figure 2. Amargosa pupfish (Cyprinodon nevadensis) are one of the most plentiful of the seven remaining pupfishes in Death Valley, and the author’s studies of how they adapt to ecologically dissimilar environments are providing insights into how phenotypes diverge in the wild. The male is the darker and larger of the two.
Photograph courtesy of Sean C. Lema.
Yet hidden in remote corners of Death Valley live the desert pupfishes—several related species that survive in an archipelago of permanent water habitats scattered in a sea of desert. Death Valley's pupfishes inhabit isolated springs, streams and marshes that are remnants of the region's milder climate less than 20,000 years ago. Since that cooler and wetter time, pupfishes in this region have evolved from a common ancestor into nine closely related species and subspecies, with each taxon living in full geographic isolation from the others. Death Valley's pupfishes are thus a little like the well-known Darwin's finches of the Galapagos Islands, in that they offer an opportunity to watch the process of evolution in action.
In the case of pupfish, variations in body shape and behavior play the role that beak sizes played for Darwin. The body shape, behavior and even the brain of a pupfish is flexible so that its development is influenced by the environmental conditions experienced during early life. This flexibility is termed phenotypic plasticity, and studies by myself and colleagues are uncovering how it plays a key role in shaping the phenotypic diversity of Death Valley's pupfishes.
You might be familiar with phenotypic plasticity in other animals. Many social insects have a division of labor within the colony where individuals have phenotypes specialized for certain tasks. In the honeybee, for example, one female serves as the colony queen and all other females act as workers. Phenotypic plasticity determines whether a female develops into the queen or worker phenotype; the diet received by a female during the first days of larval life determines which phenotype she expresses later in life. Many vertebrates also show phenotypic plasticity. Such plasticity may be a gradual phenotypic response as an individual develops or a rapid, reversible shift in behavior as an adult.
As research on phenotypic plasticity accrues, it is becoming clear that almost all traits show some plasticity. My own studies on the physiological underpinnings of variation in body shape and behavior, however, are revealing something unexpected. Patterns of phenotypic variation among pupfish populations are generated in part through the plastic developmental responses of fish to their ecologically distinct habitats. This finding suggests that what we consider population- or species-specific phenotypes can be malleable and depend in part on the development of that population in the unique habitats where they live. And when the habitats change, species' phenotypic characteristics may quickly follow......
