“重女轻男”细菌扳倒进化平衡【转】

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1、Gender-biasedbacteriathrowoffanevolutionarybalanceApril2011SweetpotatowhitefliesThismonth,biologistsreportedthatabacterialinfectionhasrunrampantinpopulationsofamajorcroppestintheSouthwest.Thebacterium(calledRickettsia)isacloserelativeofthespeciesthatcausestyphusinhumans.Itshostisthesweetp

2、otatowhitefly,atinybugthatcanoccurinlargeenoughnumberstoformvisibleclouds.Whitefliessuckthesapfromplantsandspreadcropdiseases,causinghundredsofmillionsofdollarsofdamageinasingleseason.Injustafewyears,thepercentageofsouthwesternwhitefliesinfectedwithRickettsiahasskyrocketedfrom1%tomorethan

3、90%.Unfortunately,thisisnottheboonforlocalfarmersthatitmightseem.Rickettsiadon'tsickenthewhitefly;instead,thebacteriumactivelyhelpsthepestspreadandincreaseinnumbers.Evolutionarytheoryaccountsforthissurprisingobservationandhighlightshowwemightturnitinourfavor.Where'stheevolution?Wearemostf

4、amiliarwithbacteriathatcauseillness;however,awholehostofbacterialspeciesaresymbiontsandprovidebenefitstotheirhosts.TheadvantagethatRickettsiaprovidestothewhiteflyishuge:infectedwhitefliesproducetwiceasmanyoffspringasRickettsia-freewhiteflies,andtheseoffspringaremuchmorelikelytosurvivetoad

5、ulthoodthantheoffspringofuninfectedindividuals.Whywouldonespeciesbesobenevolenttowardsanother?Theanswerseemstolieintheevolutionaryfitnessofthebacterium.Inthiscase,what'sgoodforthehostalsohappenstobegoodfortheresident.Rickettsiaaretransmittedthroughthewhiteflypopulationfrommothertooffsprin

6、g—not,forexample,betweenbugsthatalightonthesameleaf.Intermsofnaturalselection,thismeansthatanybacteriumthathappenedtohaveageneversionthatbenefitteditshost'ssurvivalandreproductionwouldbepassedontomorenewhosts.Throughmanygenerations,thesegeneticvariantswouldbecomemoreandmorecommonintheRick

7、ettsiapopulation,andeventually,bacteriathatprovidedbiggerandbiggerbenefitstothehostcouldevolve.Anevolutionaryperspectiveexplainsanotherunusualquirkofthisinteraction:Rickettsianotonlyimprovetheirhosts'reproductivecapacity,theybiasitaswell—towardshavinggirls.Uninfecte