Studies On Mitochondrial Genome And Phylogenetic Position Of Argyroneta Aquatica

Water spider (Argyroneta aquatica) is the only known spider who spend its whole life under water and that is why it differs from its terrestrial relatives. However, its systematic position is highly controversial and remains unresolved since Clerk discovered this species in 1757. Instead of getting this problem settled, some researchers, who revised and changed its systematic position purely based on morphological characters, made this issue even worse. Present viewpoint of its systematic position is really a chaos. With the widespread use of molecular data, the present viewpoint of putting Argyroneta aquatica in Cybaeidae was challenged. In the meantime, these studies had provided us with many ingenious clues that the water spider may not be a cybaeid. Furthermore, compared with the great number of sequenced insect mitochondrial genomes, the numbers of sequenced arachnid mitochondrial genomes are very scarce. This situation is even worse for spiders, with only 9 species’ mitoohondrial genome sequenced. More and more studies have proved that mitochondrial genome can be applied to molecular phylogeny and get many problems settled. Hence, the main themes of this thesis are composed by two parts. First, we sequenced the almost completely mitochondrial genome of water spider (except for a highly repeated region, about 100 bp in the control region). Arachnida phylogeny was analyzed and reconstructed by using all current avalaible arachnid mitochondrial genome sequences (9 orders and 59 species). Moreover, mitochondrial gene rearrangements were mapped into the reconstructed phylogenetic tree to test the relationships between the gene rearrangenment character and arachnid phylogeny. Second, to explore the systematic position of water spider, more spider species were sampled and sequenced. The systematic position of the water spider was analyzed by combining the data deposited in GenBank and the data from our study. The main results were as follows:1. The nearly complete mitochondrial genome of A. aquatica was sequenced through overlapping PCR fragments. The total length of all the 13 PCGs (protein-coding genes) is 10,787 bp, with an overall G+C content 30.2%, ranging from 23.9%(ATP8) to 33.8%(COX1). Most of the protein-coding genes are inferred to use ATN as start codon, which are typical for Metazoan mitochondria. The nonstandard putative start codon use of TTG is found in COX1, COX2, COX3, ND4 and ND6, respectively. Only 6 PCGs present incomplete stop codon (ND2, ND3, ND4, ND4L, ND5 and CYTB) with only a single thymine as partial stop codon. The most striking feature is well resolved relationship of Pseudoscorpiones among Arachnida. Pseudoscorpiones is not closely related to Solifugae, but a sister group of Acariformes (Acari) with high support values. Our results can notably support the monophyly of each order excluded Acari with high support values. Gene rearrangements are very common in arachnid mitochondrial genome. The water spider shares the same gene order with Habronattus oregonensis (Salticidae) and Nephila clavata (Nephilidae), but markedly differs from other 7 spiders being sequenced. Gene order seems not robust as previously proposed as useful character for distinguishing Arachnida phylogeny, but it provides phylogenetic signal in resolving some closely related groups of Arachnida.2. We added representative species of Agenlenidae, Cybaeidae, Desidae, Dictynidae and Hahniidae to comprehensively analyze the systematic position of water spider. Combined molecular data were analyzed by using molecular systematic methods, the results show that the water spider and Argenna patula are sister group. The two species form a clade belonging to the Dictynidae clade. Though other research had suggested the water spider was a sister group with Paratheuma armata, the viewpoint that the two species nested in Dictynidae clade was recovered. Our results support the close relationship between water spider and Paratheuma armata in some extent. Tricholathys sp. and Paratheuma armata together form a clade which is a sister group with the water spider clade (Argyroneta aquatica 2014+ Argyroneta aquatica 2008+ Argenna patula) with high node support (mostly are> 95%/1.00, bootstrap value/posterior probabilities).3. The monophyly of Agenlenidae is supported in our result. As we can see, the representatives of Agenleninae solely form a clade while the representatives of Coelotinae also form a clade which has a 100% bootstrap value and posterior probabilities. The remained agenlenids together form a sister group with the two subfamilies. Furthermore, our results have validated the conclusion in Miller et al. (2010) who transferred Coelotinae and Tamgrinia from Amaurobiidae to Agenlenidae.