Modularity's Role in Cranial Disparification of the Loricarioidei - A Hyperdiverse Clade of Neotropical Catfishes

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Resolving drivers of phenotypic evolution is a central goal of Evolutionary Biology. This proposal will test how biomechanical decoupling - evolutionary loss or relaxation of ligamentous linkages - affects osteological diversification, using the Neotropical catfish suborder Loricarioidei as a model. Loricarioids span >1600 species having bizarre head shapes and unique skull modifications for feeding, defence, and locomotion, such as jaws specialized to eat blood, slimecoat, or wood, and evertible cheek-teeth for competition and surface attachment. They also exhibit the variable, clade-specific absence of three major intracranial ligaments linking: 1) premaxillae to the mesethmoid, 2) bilateral mandibular rami to each other, and 3) mandibles to the opercula. An influential 1996 study found cranial disparity to be lowest in family Trichomycteridae, which retains all three linkages, and highest in Loricariidae, which lacks all three linkages, but few genera were examined and phylogenetic influence was not explicitly considered. This proposal leverages >20 years of field collections with state-of-the-art methods in phylogenomics, anatomical visualization, comparative methods, and population genomics to refine theory regarding how anatomical decoupling and modularization affects biological diversification. I will train a diverse group of 20 HQP (14 undergrads, 3 MSc, 3PhD) in innovative and integrative biodiversity research with opportunities to gain field, laboratory, and taxonomic expertise. We will generate and analyze: 1) taxon-dense phylogenetic hypotheses for Loricarioidei spanning >800 protein-coding loci, 439 species (26%), and all 170 genera, 2) a node-dated phylogenetic chronogram for loricarioid diversification using fossil and geological vicariance age calibrations, and 3) a 3D digital anatomical library comprising high-resolution cranial CT-scans from all taxa in the phylogeny. CT-based surface meshes and landmark-based geometric morphometrics will delimit the morphospace of intracranial character suites that are variably interlinked across Loricarioidei. We will use phylogenetic comparative methods to estimate diversification rates, lineage overlap in morphospace, and evolutionary convergence to adaptive peaks, and will examine speciation and selection mechanisms using SNP-based structure and demography of a highly admixed 3-species Amazonian assemblage. With an estimated origin in the Early Cretaceous, Loricarioidei has diversified throughout freshwaters of northern South and southern Central America for more than 100 Ma. They are now ubiquitous Neotropical algivores, detritivores, invertivores, and parasites. Thus, my research program will help to understand how a species-rich clade of specialized consumers diversified in one of Earth's most biodiverse evolutionary theatres, and will inform an active debate on modularity's role as a diversification accelerant and a motif capable of unifying genomic and phenotypic evolutionary theory.