Comparative Morphology And Ultrastructure Of The Male Reproductive System Of Bittacidae And Panorpidae(Mecoptera)

Bittacidae and Panorpidae are most two speciose families in Mecoptera.Previous researches mainly focused on external mophology.The internal organs are difficult to examine and relevent researches requir fresh specimens,and has thus largely been neglected,especially internal reproductive system.The reproductive system is important for the reproduction of insects as organs producing gametes and mating.The research of the reproductive system can explore its main function and understand the physiological bases of reproduction.Because the morphology of male reproductive system is conservative and has variations to some extent,it can provide valuable characters for the assessment of systematic revision.The usage of terminologies of some organs are inconsistent in male reproductive system of Bittacidae and Panorpidae.Besides,the studies of the ultratructures of male reproductive system are scarce,only the seminal vesicle and the mesodermal accessory glands are involved.The morphology and structure of the male reproductive system were investigated using light and electron microscopy in Bittacidae and Panorpidae.We also compared the morphologies of the male reproductive systems of 19 species of Panorpidae to analyse the phylogeny of Panorpidae.The main results are as follows.The male reproductive system consists of one pair of testes,vasa deferentia,epididymis,seminal vesicles,postvesicular vasa deferentia and an ejaculatory duct.The male reproductive accessory gland complexes consist of a pair of mesodermal accessory glands openning into the vas deferens,two pairs of appendices(except Bitaccidae)and paied ectodermal accessory glands located on both sides of the ejaculatory duct(except Neopanorpa).We have defined the terminologies of the organs having controversial names.The enlargement part of the vas deferens is the seminal vesicle.The middle pair of structure emerging from the seminal vesicle is the mesodermal accessory glands of Panorpidae.The inner and outer pairs of structure emerging from the seminal vesicle are the appendices.The duct connected caudal side of the seminal vesicle is the postvesicular vas deferens.The terminal part of the male reproductive system is the ejaculatory duct.The secretory modes of the male reproductive system and the gland complexes were investigated for the first time.The merocine is widespread in the organs of mesodermal origin,such as the vas deferens,the seminal vesicle,the mesodermal accessory glands and the appendices.The apocrine also occurs in the mesodermal accessory glands in Bittacidae and the seminal vesicle and the appendices in Panorpidae.The ectodermal organs mainly correspond to Class I cells sensu Noirot and Quennedey(1974),including the postvesicular vas deferens and the ejaculatory duct in both families.Only the ectodermal accessory glands correspond to Class III type.The structures and functions of the seminal vesicle,the ejaculatory duct,and the postvesicular vas deferens have been modified greatly,according to their ultrastructures.Specifically,the seminal vesicle serves a secretory function rather than storing sperm.The ejaculatory duct has thin muscular layers and a small central lumen,thus does not have the ability of ejaculating or temporarily storing a large amount of sperm.It has abundant secretory cells containing a few lysosomes,thus the main function of the ejaculatory duct may become secreting nutrients.The epithelium of the postvesicular vas deferens is enlarged to prevent the backflow of sperm and strengthens itself.We investigated the morphology of the male reproductive system in combination of other characters to analyze the phylogenetic relationship of Panorpidae.The phylogenetic analysis was conducted using the maximum parsimony analysis with TNT and WinClada.The maximum parsimony analyses yielded two most parsimonious trees and one strict consensus tree.The genera Cerapanorpa Gao,Ma & Hua,2016,Neopanorpa Weele,1909,and Sinopanorpa Cai & Hua,2008 are definitely monophyletic,but the genus Panorpa Linneaus,1758 is paraphyletic with Cerapanorpa,Dicerapanorpa Zhong & Hua and Sinopanorpa.The species of the genus Panorpa may need further split.Our results on the ultrastructures of male reproductive system of Bittacidae and Panorpidae will enable future studies of function and secretion pattern of organs.Moreover,the characters of morphology of male reproductive system have distint interspecific variations and can help to solve phylogenetic problems.We also need to cover more species in Mecoptera and provide valuable basis for phylogeny.