Evolution of Photoperiodic Time Measurement in the Pitcher- Plant Mosquito, Wyeomyia smithii

各种各样的植物和动物利用一天的长度来使它们的发育和繁殖与夏季温暖的日子同步，并在冬天寒冷的日子之前同步进入冬眠。在更北的纬度地区，白天比南纬地区的白天更长时，冬天来得更早。因此，北方生物对较长的白天做出反应，从活跃的发育切换到冬眠，以应对即将到来的冬季。许多温带动植物，包括美国一些最具问题的农业害虫，起源于更热带的纬度，或在上一次冰河时代后向北迁徙。这种迁徙需要进化出对白天的适当反应，然后移民才能在他们新的北方栖息地茁壮成长。因此，进化的对日长的反应提示了发育、繁殖和冬眠的季节性规划，代表了温带生物最普遍和最重要的适应之一。那么，问题仍然是他们如何做到这一点。在地理上相距遥远的种群内部和之间测量日长的生理基础是什么？在种群内测量日长的遗传变异背后的生理过程是否与地理距离变化的过程相同；即，了解种群内生理时钟中的遗传变异是否允许我们预测种群未来可能如何演变？PI们在一种以前的热带蚊子的温度种群中研究了这些问题。PIS发现，在南方种群中，内部生物钟(昼夜节律)在测量白天长度的过程中发挥了作用；但是，生物钟的表达随着纬度的增加而下降，因此北方种群测量白天长度基本上是一个生理沙漏。然而，当不相关的种群杂交时，它们的后代表现出回归南方或祖先的昼夜切换。这项拨款将帮助私人投资者确定恢复到祖先的日长是否也带来了生物钟的祖先表达。除了有助于我们理解生物时间测量的适应性进化的遗传和生理基础外，这项研究的结果还意味着对不断变化的环境的生理适应。如果残留的生理能力隐蔽地存在于种群中，那么对环境变化的生理适应可能比从种群中该特征的现代显性遗传变异预测的速度要快得多。如果这些隐蔽的能力是隐藏在现有种群中的祖先基因的遗迹，那么对选择的反应可能会更快地向祖先传递新的能力。因此，预测对环境变化(如全球变暖)作出反应的进化速度可能关键取决于对隐蔽或隐蔽基因在生理适应中的历史作用的理解。

A wide variety of plants and animals use the length of day to synchronize theirdevelopment and reproduction with the warm days of summer and to synchronize their entry intohibernation in advance of the cold days of winter. At more northern latitudes, winter arrivesearlier when days are longer than at more southern latitudes. Consequently, northern organismsrespond to longer daylengths to switch from active development to hibernation in anticipation ofthe forthcoming winter. Many temperate plants and animals, including some of the mostproblematic agricultural pests in the United States, originated from more tropical latitudes ormigrated north after the last ice age. This migration required evolving the appropriate responsesto daylength before the immigrants could thrive in their new northern habitats. Thus, evolvedresponses to daylength to cue the seasonal programming of development, reproduction, andhibernation represent one of the most pervasive and important adaptations of temperateorganisms. The question then remains as to how they do it. What is the physiological basis for themeasuring of daylength within and between geographically distant populations? Are thephysiological processes that underlie genetic variation for day-length measuring withinpopulations the same processes that change over geographic distances; i.e., does understandinggenetic variation in the physiological clock within populations permit us to predict how thesepopulations might evolve in the future? The PIs have pursued these questions in temperatepopulations of a formerly tropical mosquito. The PIs have found that the internal biological clock(circadian rhythm) plays a role in the day-length measuring process in southern populations; but,the expression of the circadian clock declines with increasing latitudes so that northernpopulations measure day length with essentially a physiological hourglass. Yet, when unrelatedpopulations are crossed, their offspring show a reversion to the southern or ancestral switchingdaylength. This grant will help the PIs to determine whether reversion to the ancestral daylength also brings out the ancestral expression of the circadian clock. In addition to contributing to our understanding of the genetic and physiological basis foradaptive evolution of biological time measurement, results of this study have implications forphysiological adaptation to changing environments in general. If vestigial physiologicalcapabilities reside covertly within populations, physiological adaptation to environmental changemay proceed far more rapidly than would be predicted from present-day, overt genetic variationfor that trait in a population. If these covert capabilities are relics from ancestral genes lyinglatent in extant populations, then response to selection may proceed faster towards ancestral thantowards new capabilities. Hence, predicting the rate of evolution in response to environmentalchange such as global warming may depend critically upon understanding the historical role ofmasked or covert genes in physiological adaptation.