Developmental genetic studies of the embryonic development and metamorphosis of the pedipalp using the spider Parasteatoda tepidariorum (C. L. Koch, 1841)

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The spider pedipalp is a multifunctional appendage used e.g. for feeding, sensing and mating. It therefore has an important role in adaptation and speciation in spiders. The genetical basis of pedipalp development and metamorphosis, however, is not well understood. Thus, the contribution of developmental mechanisms to the evolution of pedipalp morphology and functional diversification and adaptation cannot currently be appreciated. The aim of the project is therefore to identify genes that are required for pedipalp formation in the embryo and pedipalp metamorphosis in the post-embryonic stages in the model spider species Parasteatoda tepidariorum, and to determine their role in these processes. The project is divided into two complementary subprojects. Subproject 1 investigates the embryonic contribution to pedipalp morphology. It uses two available RNA interference (RNAi) mediated phenotypes that lead to embryonic pedipalp loss (labial-1 RNAi) and embryonic pedipalp duplication (Deformed RNAi). Differential gene expression analysis of embryonic transcriptomes of labial-1 RNAi and Deformed RNAi animals with the embryonic transcriptome of wildtype animals will thus identify the gene set required for embryonic pedipalp formation. Subproject 2 investigates the postembryonic contribution to pedipalp morphology. A special focus is placed on the formation of the bulb apparatus, which is a male specific structure used for sperm transfer and that forms in a metamorphic process before the final molt. Analysis of differential gene expression in male pedipalp tissue before, during, and after metamorphosis, and the comparison with the same tissue of age-matched females will identify the gene set controlling pedipalp metamorphosis and bulb apparatus size and shape. The function of these genes will be tested via RNAi, and a modified technique for postembryonic RNAi has been devised to affect only the metamorphosis of the pedipalp. Genes resulting in an especially interesting RNAi phenotype in Parasteatoda tepidariorum will also be isolated and studied in Parasteatoda lunata, a closely related spider species that, however, differs in bulb apparatus morphology, to provide a comparative perspective.