SG: Collaborative Research: The evolution of extreme phenotypic convergence across fish lineages in the hyper-diverse lower Congo River

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The lower Congo River is one of the most extreme freshwater habitats on Earth, with some of the planet's largest whitewater rapids and deepest underwater canyons. These rapids, eddies and canyons are home to an extraordinary array of fishes, many of which are striking in appearance and exhibit numerous adaptations to life in turbulent, high-energy waters. In such extreme habitats, evolution sometimes produces independently derived yet remarkably similar traits. For example, many distantly related fishes in the lower Congo have independently lost body coloration, have reduced or absent eyes, and share similar elongate body shapes and modified sensory features. How and when did these unusual features evolve? These striking examples of convergence (when similar traits evolve independently) strongly suggest a shared signature of selection, likely in response to the extraordinary hydrology of the river itself. This research project will examine the phylogenetic and morphological basis of convergence in the lower Congo fish fauna to address fundamental questions about the mechanisms that promote adaptation and diversification in extreme environments. These analyses will provide new insights into how limbs are reduced or lost in diverse fish lineages that can then be applied more broadly to other vertebrates. U.S. undergraduate students from a minority-serving, principally undergraduate institution will receive broad training in tropical field studies, molecular systematics, and African biodiversity more generally. Findings from the study will be incorporated within both graduate and undergraduate courses, and results will be disseminated more broadly by a Science Explorations video and project website. Other data will be deposited in online, open-access repositories. This study investigates a newly discovered system of complex in situ phenotypic convergence among members of phylogenetically diverse fish lineages. Two major datasets will be generated and integrated: 1) a phylogenetic framework based on ultra-conserved elements to determine the topology and temporal framework of within-clade divergences; and 2) a detailed morphological characterization of within-group convergence utilizing a range of quantification and visualization techniques, including 3-dimensional computed tomography (3D CT) reconstruction, histology, scanning electron microscopy (SEM), and multivariate morphometric approaches. Using these datasets, the study will investigate how rapidly these phenotypes arose, morphological correspondence of convergence within and between clades, and whether multiple traits evolved in concert. By conducting in-depth, foundational phylogenetic, anatomical, and morphometric analyses of this unparalleled natural experiment, the study will potentially transform understanding of the variety of mechanisms by which convergent phenotypes have repeatedly evolved across deep phylogenetic time. This research will also generate a broadly useful resource for future comparative studies with similar convergent systems (e.g. Astyanax cavefishes) and will establish the foundation for determining the genomic basis of these phenotypes.