RUI: Development and application of genomic resources for ascidian taxonomy and holobiont evolution

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The ascidians, informally known as sea squirts, are an important group of marine invertebrates. For instance, they are our closest invertebrate relatives, and are thus often used as models to study vertebrate development and evolution. Further, certain ascidians are very effective at invading new coastal habitats where they thrive, altering natural communities and causing considerable economic loss to the aquaculture industry. Identifying ascidian species in the wild is important but can be challenging, as they differ only subtly in their appearance and also in the short stretches of DNA typically used to identify marine species. Thus, finding a new set of DNA regions that will allow researchers to more accurately identify ascidian species and address important questions in invasive species spread will be a key aspect of this research. The research will also focus on the microbes of the sea squirt gut. These appear to play a key role in allowing certain species to succeed when they invade new regions. This research will better characterize ascidian gut microbes, shed light on whether these microbes evolve in concert with the hosts they occur in, and help shed light on the role microbes play in allowing the successful establishment of sea squirts in new habitats. This project will provide hands-on research experience for at least nine undergraduate students at three universities and will train 24 students in ascidian taxonomy, including students underrepresented in STEM. A workshop on ascidian diversity in both relatively pristine and altered marine habitats will be offered to natural resource managers and other scientists. This project will develop new nuclear genome markers across the ascidian tree of life, which will enhance opportunities to conduct phylogenetic and systematic research on the group. Further, analysis of these novel markers, along with morphological studies, will be used to survey and inventory ascidians from both harbor and reef habitats in Belize, a biodiversity hot spot for the group; information on taxonomic identification and distribution which will be made freely available as a catalog. This inventory will extend and update our knowledge of ascidian biodiversity and distribution along the Mesoamerican Barrier Reef System, a key, threatened ecosystem. It will also document the prevalence of introduced ascidian species and provide identifications based on integrated molecular and morphological data for over 40 species never previously sequenced. Furthermore, this project will characterize the microbiome of the ascidian gut. This microbiome plays a key role in allowing certain ascidians to successfully invade new habitats and may have been important in ascidian evolution. The variation in structural (taxonomic groups) and functional (specific gene) features will be mapped out across the ascidian tree of life to provide more insight into the role of microbial symbionts in ascidian evolution. By combining morphology with newly developed molecular markers, applying this integrative approach to introduced species identification, and investigating microbial symbiosis as a driver of ascidian evolution, this project will significantly advance our understanding of ascidian diversity and phylogenetics and the factors promoting biological invasions.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.