Convergent evolution of a reproductive trait through distinct developmental mechanisms in Drosophila

摘要

Convergentmorphologiesoftenariseduetosimilarselectivepressuresinindependentlineages.Itispoorlyunderstoodwhetherthesameordifferentdevelopmentalgeneticmechanismsunderliesuchconvergence.Hereweshowthatindependentevolutionofareproductivetrait,ovariolenumber,hasresultedfromchangesindistinctdevelopmentalmechanisms,eachofwhichmayhaveadifferentunderlyinggeneticbasisinemDrosophila/em.OvariolenumberinemDrosophila/emisspecies-specific,highlyvariable,andlargelyundergeneticcontrol.ConvergentchangesinemDrosophila/emovariolenumberhaveevolvedindependentlywithinandbetweenspecies.Wepreviouslyshowedthatthenumberofaspecificovariancelltype,terminalfilament(TF)cells,determinesovariolenumber.HereweexamineTFcelldevelopmentindifferentemDrosophila/emlineagesthatindependentlyevolvedasignificantlylowerovariolenumberthantheemD.melanogasterOregonR/emstrain.WeshowthatintheseemDrosophila/emlineages,reductioninovariolenumberoccursprimarilythroughvariationsinoneoftwodifferentdevelopmentalmechanisms:(1)reducednumberofsomaticgonadprecursors(SGPcells)specifiedduringembryogenesis;or(2)alterationsofsomaticgonadcellmorphogenesisanddifferentiationinlarvallife.MutationsintheemD.melanogaster/emInsulinReceptor(emInR/em)alterSGPcellnumberbutnotovarianmorphogenesis,whiletargetedlossoffunctionofembric-agrave;-brac2/em(embab2/em)affectsmorphogenesiswithoutchangingSGPcellnumber.Thus,evolutioncanproducesimilarovariolenumbersthroughdistinctdevelopmentalmechanisms,likelycontrolledbydifferentgeneticmechanisms./p/div