死寂的沼澤地“死亡谷”目前仍是北美洲海拔最低、最干燥,、最熱的地區(qū),，其中生存著一種類似加拉帕戈斯群島達爾文雀的沙漠魚pupfish,，人們可以觀察到其進化的全過程，它正揭示著環(huán)境如何重塑著動物的體型和行為,。
Pupfish的體型,、大腦和行為都很靈活，其發(fā)育受早年環(huán)境的影響很大,。這種靈活性稱為表型可塑性,，它對pupfish表型多樣性的形成起著關(guān)鍵作用。許多動物如蜜蜂和脊椎動物都有表形可塑性,。一些特殊表型的形成取決于他們特殊的棲息地,，一旦棲息地變了，表型特征也會發(fā)生變化,。死亡谷中的水溫不適宜pupfish的生存繁衍,，其中著名的“魔鬼洞”是pupfish唯一天然的棲息地?？伤苄砸彩怯羞z傳基礎(chǔ)的,，由生物個體的染色體組和生存環(huán)境共同決定。一個適應(yīng)性進化的新方向取決于生物體本身是可變異的,，這種變異共同取決于基因型和結(jié)構(gòu),、生理、行為上的表型可塑性,。
Pupfish的行為有賴于其棲息地的環(huán)境,，而對唯一棲息地的過分依賴會使魔鬼洞的pupfish極易滅絕，為此人們建了三個模仿魔鬼洞環(huán)境的避難所,。5年后發(fā)現(xiàn),，避難所中與魔鬼洞中的pupfish的表型差異很大，這正是環(huán)境差異使然,。這些差異還包括攻擊性和求愛行為的差異,。對pupfish表型可塑性的探索日益緊迫，因為魔鬼洞從1990年開始就不明原因的在縮小,。既然表現(xiàn)型由基因型和環(huán)境共同決定,，因此，我們將如何努力保護特殊的基因和在特殊環(huán)境下生長的物種呢,？ （陳仁杰/編譯）
生物谷推薦英文原文：
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......
