The Systematic Position,Population Differentiation And Bioacoustics Of The Genus Subpsaltria

Males of most species of cicadas are particularly known for their loud and amazing varieties of sounds.The main method of sound production in cicadas is the tymbal mechanism which has been described in detail.In Cicadoidea,besides the tymbal organs,stridulatory systems have also been developed in a few species.However,studies on these peculiar cicadas have been almost entirely ignored.In China,Subpsaltria yangi Chen is the sole cicada species which possess both tymbal and stridulatory organs.Here,the cicada S.yangi is used as study species.We focus on three objectives:(1)we conduct molecular phylogeny analysis to determine the systematic position of the genus Subpsaltria;(2)we use molecular markers to explore the degree of genetic divergence between populations;and(3)bioacoustics of this cicada species is investigated.Mitochondrial and nuclear DNA data(i.e.CO?,CO? and EF-1a)were used to explore the phylogeny of Subpsaltria and other related taxa.We use maximum parsimony(MP),maximum likelihood(ML)and Bayesian(BI)methods to conduct phylogenetic analysis.The inferred phylogeny trees show that S.yangi and all species of Tibicina Amyot are grouped into a monophyletic clade.Furthermore,the genetic distances between S.yangi and the species of the genus Tibicina are within the range of distances among taxa of the Tibicina.These results suggest that Subpsaltria should be synonymized with Tibicina.We use four mitochondrial genes(i.e.CO?,CO?,Cytb and A6A8)and one nuclear gene(i.e.ITS1)to investigate the degree of genetic divergence among eight populations of S.yangi.The phylogenetic trees(ML and BI trees)indicate that all specimens of the population from Mts.Helan in Ningxia Hui Nationality Autonomous Region are all clustered into a clade.The populations from Shaanxi and Shanxi provinces are not clustered in their own clades.These results suggest that there is genetic divergence between the population from Ningxia and populations distributed in Shaanxi and Shanxi.In addition,the genetic distance estimates in this study show that the genetic divergence between the populations does not reach species level.The potential influence of geographical barriers and ecological differences on population divergence and allopatric speciation is discussed.Based on morphological studies,behavioral observation,acoustic analysis and acousticplayback experiments,we investigate the acoustic behavior of S.yangi.Both males and females of S.yangi possess stridulatory organ,and the morphology of the stridulatory organ is similar in both sexes.The file is a modification of an area on the anterior angle of the mesonotum,and the base of the inner margin of the forewing is slightly curved outwards,functioning as the scraper.We reveal that males of S.yangi can emit sounds using both tymbal and stridulatory mechanisms,and the females are able to produce sounds by the stridulatory organ.Our study provides the first experimental evidence for sound production by a stridulatory mechanism in cicadas.Females of this cicada species prefer to produce sounds from concealed perches,e.g.the canopy of the shrubs,and grasses.In contrast,the males generally produce sound signals from high and exposed perch sites.Predation and sexual selection may result in males and females of S.yangi choosing different places to produce sounds.The sounds produced by both males and females of S.yangi function in the context of pair formation.The process of pair formation of S.yangi is as follows:(1)males use both their tymbal and stridulatory organs to produce advertisement signals;(2)sexually receptive females emit sounds in response to advertising males;and(3)the males rely on females' acoustic responses to locate and find females.The post-copulated females of this species are no longer able to produce sound signals.In S.yangi,the forewings would strike the body during performing stridulatory sound-producing movements,which generate impact sounds.However,the impact sounds play no role in acoustic communication.Acoustic analyses show that the stridulatory sound signals produced by males are extremely similar,if not identical,to those of females,which indicates that males mimic the signals produced by females during pair formation.Acoustic playback experiments suggest that,by producing female-like sound signals,a male can deceive a receptive female into treating him as a rival female,which makes the male more effective in eliciting acoustic responses from the receptive female.Therefore,the males can gain reproductive benefit by mimicking female sound signals,since they rely primarily on females' acoustic responses to find females.In addition,we find that one type of sound produced by our mouths can effectively attract the males of this cicada species.Acoustic playback experiments and signal analysis suggest that the reason why S.yangi males exhibit this abnormal phonotaxis behavior is that the male cicadas mistake the sounds produced by our mouths for acoustic signals of conspecific females.The cicada species of the genus Karenia Distant,similar to S.yangi,can produce sounds using their forewings.Therefore,the acoustic behavior of one species of Karenia(i.e.K.caelatata Distant)is also investigated and is compared with that of S.yangi.Although both S.yangi and K.caelatata have the ability to produce sounds by means of forewing movements,the sound-producing mechanism of S.yangi is different from that of K.caelatata.On thebasis of behavioral observations of individuals when producing sounds,we find that males of K.caelatata can produce sounds by banging the forewing costa against the corresponding operculum.This is the first known case of a cicada species producing sounds with this type of mechanism.The structures involved in sound production of K.caelatata(i.e.forewing,operculum,cruciform elevation,and wing-holding groove on scutellum)are all morphologically modified.The sounds produced by K.caelatata males are used in intraspecific communication and function as calling songs.