Characteristics To Adapt Cave Environment And Molecular Phylogeny Of Diestrammena Caverna Sp. N.

Diestrammena caverna sp. n. is a recently reported new cave-dwelling insect species, which belongs to Orthoptera, Rhaphidophoridae. Morphological and biological characteristics of Diestrammena caverna sp.n. were studied through laboratory rearing and field investigation. Under the scanning electron microscope and microscopic observation, specific structure characters that well-adapted to the cave environment such as antennal receptor, mid-gut, proventriculus, Malpighian tubeles cell and ovary cell were specified. Moreover, the phylogenetic relationships are established together with molecular evolution phylogenesis by using 16S rDNA sequenxes. The main results are as follows:1. Characters associated with adaptability to the cave environment1.1 MorphologyThe length of adult body is approximately 11.0-12.Omm, which is charactered as snuff color and dust-color dapple. It has two coniform prominency, filamentous antenna, various and large quantity of receptors, strong scape, short pedicel with a dent inside, a markedly longer fist flagella. Also, its compound eyes consist of a certain amount of ommatidias, which is hemispherical. Maxillary palpus is slight and Labial palpus is relatively thick and strong covered by sensilla. Legs are acerose and tibias of hind leg have 28-48 stabs. Ovipositor is knife-shaped, acerose and hard. Newly-oviposition eggs are ivory and then turn brown when they are about to hatch with alveolar grain. The most remarkable character of the adult is to be covered with dense sensilla and is highly-sensory. It enables the adult to detect the enemies and foods quickly to well adapt to the cave environment.1.2 BiologyDiestrammena caverna sp. n. takes two years to finish one generation. Nymphal stage is relatively long with 8-14 months. Nymphae inhabit dark and damp rock tunnels in the cave and mainly feed on litter and dead bodies of other cave organisms. In addition, they also feed on ecdysis of their own as supplemental nutrition. The adult stage usually lasts 6-10 months. The female mate and oviposit for several times, and 2-8 eggs for each egg-laying. The eggs were laid in a scattered way in damp rock tunnels and the egg stage usually last 3-4 months. 1.3. Antenna sensillaSeven kinds of antenna sensillas were found in the antenna of adult:sensilla trichodea, sensilla chaetica, sensilla coeloconic, sensilla squamiforma, sensilla auricillica, sensilla basiconica and one new sensilla. Sensilla trichodea and sensilla chaetica were mainly found in flagella, sensilla coeloconic and sensilla squamiforma in pedicel. Sensilla auricillica were only observed in flagella venter of the male adult and sensilla basiconica were scattered in scape. In addition, a new antenna sensilla tribar was found which has not been reported before. The sensilla tribar were mainly in the dimple of the antenna’s surface. Each sensilla has protrusions with three tiny ones. The features of the antenna sensillas can be described as various and substantial, which enables Diestrammena caverna sp. n. to detect and escape enemies and to reach food quickly, effectively adapting to the dark cave environment.1.4. CellularityThe cells of mid-gut were closed and crimped, which increase the digestive area of the mid-gut and therefore raise the utilization for the foods. There is large quantity of teeth in the proventriculus and the structure was complex along with muscle layer. This was favorable to grind food and thus increase the utilization of foods. Large amount of cells in Malpighian tubeles and strong muscle fibers in basement membrane were also favorable to reabsorbing. There was few ovarioles but they were large, which could ensure the sufficient nutrition required for the development. These are indicators for Diestrammena caverna sp.n. to be well adapted to the cave environment regarding the food utilization and reproduction.2. Molecular PhylogenyThe fragments of 16S rDNA of 2 species from genus Diestrammena were compared with that from the 41 homologous sequences of genus Dolichopoda downloaded from the GenBank data library. The molecular phylogenetic trees were reconstructed by using Hadenoecus cumberlandicus、Euhadenoecus insolitus、Ceuthophilus gracilipes and Troglophilus cavicola as complex outgroups with NJ and ME methods, based on the Model Kimure-2 of MEGA software. There were 188 variable sites,133 parsimoney informative sites and 329 conserved sites from the 521bp sequences obtained. The average content of A, T, C and G were 35.15%、37.1%、10.625% and 17.125%, respectively. The base compositions had A+T bias. Among the 20 kinds of amino acid, Leu, Asp, Phe and Ser are in high level. Most of the Dolichopoda is free of Arg (except for TS and WN in China). The phylogenetic trees showed that the ingroup were divided into 6 clades. They were Greece i cluster, Russia cluster, Italy cluster, Greece II cluster, Turkey cluster and Diestrammena in China, among which Diestrammena was closed with turkey cluster than other relatives.In this study, the adaptability to the cave environment of Diestrammena caverna sp.n. was revealed by studying the biology, morphology, antenna sensilla and the character of cell structure. Also, the phylogenetic relationships were investigated by using molecular evolution approach. The results served as basis for the evolution of genus Diestrammena insects and also deepen the study of cave insects and conservation in China.