The Caenorhabditis elegans dauer larva: Developmental effects of pheromone, food, and temperature☆

摘要

Threeenvironmentalcuesinfluenceboththeentryintoandexitfromthedevelopmentallyarresteddispersalstagecalledthedauerlarva:adauer-inducingpheromone,food,andtemperature.Thepheromone,whichisameasureofpopulationdensity,inducesdauerlarvaformationatthesecond(L2)moltandinhibitsrecoveryinadose-dependentmanner.Foodactscompetitivelytoreducethefrequencyofdauerlarvaformationandtoenhancerecovery.Thepheromonecausesaspecificextensionofthesecondlarvalstage,coupledwithatransientdecreaseinthegrowthrateoftheL2.Second-stagelarvaegrowninthepresenceofaddedpheromonearemorphologicallydistinguishablefromL2larvaegrownwithoutpheromone.Wehavenamedthepre-dauerL2larvatheL2d.CommitmenttodauerlarvaformationcanoccurattheL2dmolt.WhenL2dlarvaeareshiftedoutofpheromonetoalawnofE.colijustbeforetheL2dmolt,afewwormscompletedevelopmentintodauerlarvae.Incontrast,wormsareessentiallycommittedtothenon-dauerlifecyclebythefirstlarvalmoltiftheL1larvaearenotgrowninappropriatelyhighlevelsofpheromone.Inthepresenceofpheromone,thepercentageofdauerlarvaformationisenhancedathighertemperatureswithinthenormalgrowthrange.Temperaturedown-shiftsinducedauerlarvarecovery.Temperature-shiftexperimentsshowthattheenhancementofdauerlarvaformationrequiresexposuretothehighertemperaturearoundtheL1molt.Twosensorymutantsdefectiveinthermotaxisarealteredintheirsensitivitytothedauer-inducingpheromone,buttheirpheromoneresponseretainstemperaturedependence.Responseofdauerlarvaetoenvironmentalcuesishighlyagedependent,witholderdauerlarvaeexhibitinganincreasedtendencytorecover.