ARTS: Taxonomy and Molecular Systematics of Mesh Web Spiders (Araneae: Dictynidae)

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Spiders are an incredibly diverse group of organisms that play an essential role in ecosystems all over the world. In spite of their notoriety and the fear that they often inspire, huge gaps in our knowledge remain for some groups of spiders. Often generalized as small and brown or grey, many spiders in the family Dictynidae are quite colorful, and are perhaps most notable for their intriguing distributional patterns and fascinating ecological characteristics. In fact, this “dark corner” of the spider tree of life comprises a group that occupies virtually every terrestrial ecosystem on earth and contains the only fully aquatic spider species. While some species are endemic to very small areas, others are some of the most widespread of all spider species. This level of variation within a single family of spiders shows considerable potential as a system for answering a broad range of evolutionary and ecological questions, especially as they relate to the evolution of specific characteristics or behaviors. This project aims to resolve the evolutionary relationships among this group of spiders and their relative position within the spider tree of life, shining a light on one of the most poorly known parts of the spider tree of life. Additionally, a main goal of this project is to train the next generation of taxonomic experts, organismal biologists and systematists in Dictynid spiders in the US. Dictynidae are a hugely diverse family nested within the “marronoid clade”. Because the relationships of the genera, of species in the genera, and the relationship of the family within the spider tree of life, are largely unknown, efforts to ask interesting questions in an evolutionary context are stymied. We aim to open the door to evolutionary and ecological studies of the group by creating a taxonomic and phylogenetic scaffold in support of further research for years to come. We will accomplish this by: 1) Revising the moderately diverse, unusual genus Lathys using morphological data and data gathered from Next Generation Sequencing (NGS); 2) Determining the phylogenetic relationships of all dictynid genera using NGS data; 3) Using NGS data to determine the placement of Dictynidae within the spider tree of life. We will collect both specimens of Lathys and representatives of all dictynid genera worldwide with our multinational team of collaborators. Standardized images from all specimens, including types, will be produced using high-resolution stacked images, SEM micrographs, and microCT scanning of nearly 50 amber fossils to allow for consistent morphological analysis. Low coverage genome sequencing will be used to produce molecular data that will be incorporated with the morphological matrix to subsequently be analyzed using Bayesian Inference. This method allows the analysis of a combined morphological and molecular dataset, paramount for the inclusion of fossil taxa, which subsequently allows us to use tip dating to produce a time-calibrated phylogeny. We will conduct these analyses separately at three taxonomic scales: Lathys, all dictynid genera, and the “marronoid clade”. We will use probabilistic inference on the resulting Lathys phylogeny to test Laurasian biogeographic hypotheses. Finally, ancestral state reconstruction will be conducted to examine the evolution of morphological characters as well as ecological and behavioral characters, including aquatic habitat association and hunting strategy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.