Correlation Between Flower-visiting Behaviors Of Colocasiomyiaflies And Flowering Phenology,Thermogenesis Rhythm,and Floral Odor Composition Of Rhaphidophoralaichouensis

The aroid plant Rhaphidophora laichouensis Gagn.belongs to the subfamily Monsteroideae,family Araceae.Compared to the spadices in the subfamily Aroideae(characterized by unisexual florets,distinct spadix zonation,and presence of an appendix)of the same family,the spadices of Monsteroideae are characterized by bisexual florets,less zonation,and absence of appendix.Previous studies on Aroideae plants revealed varied effects of the flowering thermogenesis,i.e.,promoting the synthesis and emission of the floral scents,which are attractive to the Colocasiomyia flies visiting the inflorescences.In addition,the heat produced by the inflorescences also serves as reward to the pollinating flies,which depend on the host throughout their entire life cycles,thus evolved intimate mutualism with their host plants,forming ideal system for studies of mutualism evolution.In this study,the phenology of Rhaphidophora laichouensis during the anthesis,as well corresponding flower-visiting behaviors of the Colocasiomyia flies utilizing this plant were,were observed,with temperatures at different parts of the spadix and the ambient temperature recorded using a data-logger thermometer for multiple days.In addition,samples of floral scent chemicals were collected and analysis using the SPME as well GC-MS methods.The results are summarized as the following:1.The flowering process of R.laichouensis lasts about five days,and can be divided into five stage:Stages ?-?,with Stages ?-? correspond to the female phase,while the Stages ? and ? correspond to the male phase.2.The inflorescences of R.laichouensis generate small amplitude heat before the anthesis.Two peaks were found during the anthesis,at the Stages ?(female phase)and?(early male phase),respectively.Comparison of temperature revealed highly consistent rhythm as well amplitude among different(proximal,medial and distal)portions of the inflorescence of R.laichouensis.This results is consistent with the specificity floral traits(i.e.,bisexual florets,spatially undifferentiated spadix)of R.laichouensis,thus revealed quite different flower thermogenetic pattern between Monsteroideae and Aroideae.3.The behaviors of the Colocasiomyia flies(most were identified as of C.longivalva.with the remaining as of C.hailini and other species of the C.giganlea group)on the inflorescences of R.laichouensis showed intimate synchrony with the flowering phenology of the host.Before the anthesis,no Colocasiomyia flies was found on the inflorescences,while in the Stage ?(the initial anthesis),the slight heat production was detected,resulting slightly higher temperature of spadix than the ambient one.At the same time,the Colocasiomyia flies are attracted to the spadix by strong floral odor.During the Stages ?,the spathe loosed more,the first distinct peak of heat generation was detected,strong floral odor can be smelled,and more Colocasiomyia flies were attracted to the spadix.During the Stage ?,the spathe became fully open,and the second distinct peak of heat generation was detected,and strong floral odor smelled,more Colocasiomyia flies were observed feeding,mating,or ovipositing on the spadix.During the Stage IV,the spadix continued to release some pollens,but no heat generation was detected,and the Colocasiomyia flies,all dusted with pollen grains,left the inflorescence.During the Stage V,the stamens withered/decayed,all the flies left the inflorescence,leaving their eggs in slits between pistils.The 1st-instar larvae are expected to hatch after the ripening of the infructescence.4.A total of 45 volatile organic compounds(VOCs)were detected in the GC-MS analyses of the R.laichouensis floral scent samples,each from four inflorescences.The main constitutents of the compounds proved to be 3-pentanone,?-piperine,2-pentenol and 1,8-eucalyptine,with the first one(3-pentanone),which had the highest relative concentration,was considered as key component to attract the flies.The 3-pentanone had been commonly detected in the previous studies of angiosperm plants,including those of the subfamily Monsteroideae,but not the subfamily Aroideae,indicating that this trait(i.e.,3-pentanone serving as component of floral scent)may had been possessed by the MRCA(most recent common ancestor)of the angiosperm plants but lost in the subfamily Aroideae.This provide us with evidence for tracing the adaptation history of Colocasiomyia flies to their aroid hosts,and the evolution of the mutualism between them.The above results indicated that the flower-visiting behaviors of Colocasiomyia flies(most are adults of C.longivalva)are closely related to the flowering phenology,the thermogenesis rhythm and the floral odor composition of R.laichouensis.The 3-pentanone serving as component of floral scent of R.laichouensis may had been possessed by the MRCA of the angiosperm plants but lost in the subfamily Aroideae.The interaction pattern varied with the taxa of the flies(i.e.,flies of the C.gigantea group or not)as well the hosts(i.e.,hosts from the subfamilies Monsteroideae or Aroideae hosts).The present study provide more evidence for the intimate mutualism has been evolved between the Colocasiomyia flies and their host aroid hosts.