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Species delimitation of the orchard-spider Leucauge venusta (Araneae, Tetragnathidae), the phylogeny of Leucauge and the identification of orthologous genes from transcriptomes Open Access

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The genus Leucauge (Tetragnathidae, Leucauginae) includes 174 described species from the tropical and subtropical regions of all continents with the exception of Europe and Antarctica. In this dissertation, evolutionary questions at different hierarchical levels are explored using the spider genus Leucauge as case study. At the microevolutionary scale, we test the species boundaries of the North American orchard spider Leucauge venusta using two genetic markers. The analyses clearly separate USA populations in two deeply divergent and geographically structured groups (North-South). We restrict the name L. venusta to the Northern clade and remove L. argyrobapta from its synonymy for the southern clade. We present the first attempt to unravel the phylogenetic relationships within this genus and their placement within Leucauginae based on traditional PCR targeted sequences from five loci commonly used in spider systematics plus Histone H4, used for the first time in spider phylogenetics. We include an assessment of the informativeness of the standard markers and test for base composition biases in the dataset. The results suggest Leucauge is not monophyletic as it includes species currently placed in the genera Opas, Opadometa, Mecynometa and Alcimosphenus. Evolutionary studies in spiders have been limited to comparisons of a relatively small number of genetic markers. At the same time, high throughput sequencing technologies are making available large amount of data which can potentially be used in the search of orthologous loci of utility in spider phylogenetics. We present a bioinformatic pipeline, including a new phylogenetic orthology criterion, to find orthologous gene groups from a collection of anonymous genomic sequences. The pipeline is demonstrated on a trivial gene family tree using vertebrate hemoglobins, asmall dataset from insect genomes and collection of 27 spider transcriptomes including Leucauge venusta. Using this new method, we were able to identify thousands oforthologous loci potentially useful for spider phylogenetics.

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