A Preliminary Study On The Phylogeny Of Entomobryinae(Collembola,Entomobryidae)

Collembola,commonly known as springtails,is widely distributed in various terrestrial ecosystems.It is one of the three soil animals(nematodes and mites)and its diversity plays an irreplaceable role in litter decomposition and nutrient cycling.As small and medium sized soil animals,Collembola is characterised by its specialised abdominal appendages,tenaculum(furca-holding organ)and jumping organ(furcula).At present,the external morphology is still the main tool for the taxonomy of Collembola.Entomobryinae has the greatest diversity in species and morphology among entomobryid subfamilies,and thus it is of great importance in systematics.However,the current morphological classification in Entomobryinae has encountered many bottlenecks,the understanding of morphological characteristics is full of controversy,and the phylogeny of the subfamily has not been resolved.A preliminary study on the phylogeny of Entomobryinae by sampling main genera is conducted here.The dissertation includes four chapters.In the first chapter,the history of collembolan taxonomy,including detailed morphological features and the historical development of systematics are reviewed,summarizing the current taxonomy and phylogeny of Entomobryinae and Entomobrya.In the second chapter concerns materials and methods of the study,containing species sampling,sequencing,assembling and data analyses,etc.In the third chapter,one new genus and three new species are described,with the Entomobryinae redefined.Body scales are fundamental in the classification of Entomobryidae at all taxonomical levels.Traditionally,scales on dens were considered to be absent in Entomobryinae,but present in other scaled subfamilies;however,this opinion was strongly challenged by recent morphological advances in tergal specialised chaetae(S-chaetae).A new genus,Lepidodens,is strikingly similar to the scaled Entomobryinae genus Willowsia in having pointed scales with relatively long ribs and 2,2|1,2,2,8,3 tergal S-chaetae,but differs from it in having dental scales and a unique position of S-microchaetae on the first abdominal segment.Multilocus phylogeny based on COI,16SrRNA,18SrRNA and 28SrRNA Dl-2 and topology tests also support this view,the new genus clustering with Entomobryinae rather than Seirinae.Three new species,L.nigrofasciatus,L.similis and L.hainanicus,are described from South China.This study clearly undermines the traditional separation of Entomobryinae and Seirinae/Lepidocyrtinae,and demonstrates that dental scales could occur in all entomobryid subfamilies containing scaled taxa.In this new phylogenetic hypothesis,Entomobryinae has the greatest diversity in scale morphology and distribution among scaled collembolan groups,indicating multiple independent origins of scales.The fourth chapter,based on Entomobrya,the largest genus in Entomobryinae,we conduct a preliminary study on the phylogeny of Entomobryinae.Highly diversified colourations among springtails have been widely used for species diagnosis,but their phylogenetic significance is poorly unknown.We addressed this issue in Entomobrya,which possessed variable colour patterns among species.Based on the material mainly from China,we have conducted a multilocus phylogeny and topology tests with likelihood and Bayesian algorithms,and accordingly demonstrated the non-monophyly of Entomobrya and the phylogeny of Entomobryinae was unresolved.The division of five clades,including Entomobrya and several related genera,coincided well with five types of colourations,respectively.Further analyses of divergence time and historical biogeography revealed that Chinese Entomobrya originated mainly from Palearctic(northern and western)China in the Paleocene and Eocene.This study highlights the great phylogenetic values as well as taxonomic uses of colouration in Entomobrya.Multiple phylogenetic and biogeographic origins of Entomobrya imply its complicated relationships with both scaled and unscaled genera of Entomobryinae.