Morphology And Ultrastructure Of Spermatozoa In Seven Cicada Species From China(Hemiptera:Cicadidae)

Spermatozoa are a special kind of cells with diverse morphology and ultrastructure.Sperms of different insect groups have unique characteristics and can provide important information for taxonomic and phylogenetic analyses.So far,only the sperm structure in the family Cicadidae,i.e.,only 13 species belonging to 11 genera of subfamilies Cicadinae,Cicadettinae,and Tettigomyiinae have been reported.No research on the spermatozoa of the subfamily Tettigadinae has yet been conducted.In order to further clarify the sperm morphology and ultrastructure of cicadas and provide more information for taxonomic and phylogenetic analysis of Cicadidae,the mature spermatozoa of Subpsaltria yangi,Tettigetta sp.,Karenia caelatata,Platypleura kaempferi,Meimuna mongolica,Cryptotympana atrata,Pycna repanda of Cicadidae were investigated in the present thesis using fluorescence and transmission electron microscopies,respectively.The main findings are as follows:The sperm morphology and ultrastucture of these seven cicada species are similar.The filiform spermatozoa aggregate into bundles,and their heads are embedded in a homogenous matrix to form the spermatodesmata.The head region contains a short acrosome and a nucleus.The neck region consists of a centriole and a centriolar adjunct,and the centriole is located at the end of the nucleus;the centriolar adjunct is the main organelle connecting the head and the tail region,which is located at the posterolateral invagination of the nucleus.The tail region generally consists of a single axoneme and a pair of symmetrical mitochondrial derivatives,but some sperms of certain species have multiple axonemes and mitochondrial derivatives.The axoneme is a typical 9 + 9 + 2 arrangement of microtubules(i.e.,9 accessory microtubules,9 doublet microtubules,2 central microtubules).The mitochondrial derivatives consist of regularly arranged cristae,and each derivative has a single crystalline region.At the end of the flagellum,the microtubes of axoneme are irregularly arranged or disappeared.The length of spermatozoa is significantly different within and between species,viz,polymegaly.According to the various length of spermatozoa,spermatozoa of K.caelatata and Py.repanda can be divided into three types: Long spermatozoa,Medium spermatozoa,and Short spermatozoa;the other five investigated cicada species(S.yangi,Tettigetta sp.,Pl.kaempferi,M.mongolica,and C.atrata)can produce only two types of spermatozoa: Long spermatozoa and Short spermatozoa.An electron-dense deltoid region was observed in the sperm tail of K.caelatata and Py.repanda in the Cicadinae which has not been found in other cicadas.Spermatozoa of C.atrata possess less electron-dense nucleui which are distinctly different from other known cicada species.A significant difference also performs in the structure of the centriolar adjunct of sperms among different subfamilies of Cicadidae,i.e.,the centriolar adjunct appears to be a sheath structure in Cicadinae,a lamellar structure in Cicadettinae,and a granular structure in Tibicininae.Our results indicate that a lamellar centriolar adjunct is a synapomorphy of Cicadettinae.The results of this study indicate that the difference in structure of the centriolar adjunct may serve as an important feature in distinguishing the three subfamilies within Cicadidae.Based on the ultrastructure of the centriolar adjunct of spermatozoa combined with other related morphological features,it is more reasonable to assign K.caelatata to Cicadinae instead of Cicadettinae.In addition,we observed that there are multiple axonemes and mitochondrial derivatives in one flagellum of some spermatozoa,which may be related to that the flagellum can provide available genetic material(cytoplasmic inheritance)for fertilization,and to that the flagellum provides motility(competitiveness)to the sperm during copulation.In comparison with the spermatozoa of the other two groups within Cicadomorpha(i.e.,Membracoidea and Cercopoidea),only the spermatozoa of Cicadidae exhibit polymegaly.The differences in the sperm morphology and ultrastructure of different groups of Cicadidae can provide significant information for the taxonomy of Cicadidae and the phylogeny of the Cicadomorpha.