Rotifers are tiny (≤2 mm) invertebrate animals that can be found anywhere there is liquid water. For instance, they inhabit shallow sea water, lakes, ponds, streams, irrigation ditches, ephemeral basins in deserts, meltwater puddles on glaciers, and thin layers of water on soils and plants. Rotifers play vital roles in ecological systems as both predators and prey, and the nutrients they contain are passed up the food chain to insects and fish. Scientists study rotifers to better understand aging, aquaculture, ecology, development, and the evolution of reproductive modes. A fascinating feature of rotifers are their complex life cycles: some alternate generations, whereas others primarily reproduce by creating clones of themselves. This work will use genetic analyses and comparisons of anatomy that rely on advanced microscopic imaging to determine the evolutionary history of a major group of rotifers and examine how life cycles and reproductive mode changed as the group evolved. Many species from diverse habitats will be considered, and the research will also result in better characterization of the life cycles of species that are poorly known. As part of the project, educational workshops and museum displays will be produced, contributions will be made to online databases, and a scientific symposium will be held at a national meeting. Further, a postdoctoral scientist, along with graduate, undergraduate, and high school students, will be trained to conduct studies of this diverse animal group.

The goal of this project is to build a comprehensive phylogeny of rotifers with a focus on the Class Monogononta, the most speciose and diverse lineage in the phylum. This research will provide a framework for testing how the diversification of the group is associated with the origins of different reproductive modes. The project has three aims. (1) It will produce a comprehensive phylogeny of rotifers using molecular sequence data and morphology; the morphological studies will utilize conventional electron microscopy, focused ion-beam scanning electron microscopy, atomic force microscopy, and confocal laser scanning microscopy; the morphology of at least 100 species representing nearly 90% of family diversity will be considered. (2) It will use the phylogeny and ancestral state reconstruction methods to investigate questions concerning the evolution of reproductive traits in rotifers. In particular, (a) how did the maternal provisioning of nutrients (i.e., matrotrophy) and internal brooding evolve from egg-laying species? (b) how did the ability to produce both mitotic and meiotic ova in a single animal evolve from cyclical parthenogenesis? (c) do eggshells produced by species with different reproductive modes show similarities in morphology, chemistry, and mechanical properties, and are these correlated with life history traits? And (d) has the small size of certain life cycle stages evolved more than once? (3) The phylogeny will also be used to identify monophyletic groups, present a predictive classification of rotifers, revise or produce new diagnoses for taxa above the genus level, and produce species keys. Additionally, because Rotifera is the most diverse clade (>2000 species) and the only gonochoristic group within the larger lineage Gnathifera (~3575 species from five higher taxa: Chaetognatha, Gnathostomulida, Micrognathozoa, Rotifera, Acanthocephala), rotifers are ideal candidates to provide insights into gnathiferan evolution and help answer questions about the evolution of reproductive diversity, jaws (e.g., Gnathifera), and parasitism (e.g., Acanthocephala).

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.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Bruce Lieberman
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University of Texas at El Paso
El Paso
United States
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