Meeting Abstract
Body elongation is one of the most prominent aspects of morphological diversification in fishes. Evolutionary transitions between disc-shaped, fusiform, and eel-like bodies involve some combination of changes to head shape or vertebral dimensions, but it is unknown whether major shifts in body shape require particular suites of anatomical changes. In this study, we investigate the evolutionary origins of the remarkable diversity of body shape within Pelagiaria—a radiation of open-ocean fishes containing 15 recognized families that span much of the range of body shapes exhibited among ray-finned fishes. Using a robust fossil-calibrated molecular phylogeny and a Bayesian method for estimating the adaptive landscape, we identify shifts in optima for overall body shape and for the anatomical components that determine it. We estimate a relatively deep-bodied pelagiarian ancestor, a shift to a fusiform optimum that is widely shared among lineages (e.g., tunas and mackerels, bluefish), and several transitions to elongated forms. One of these transitions—the one leading to the highly elongated Trichiuridae (e.g. cutlassfishes)—is associated with shifts in optima for most underlying anatomical components (i.e., lengthening of the head and abdominal and caudal vertebral regions). Other instances of body elongation, however, are associated with peak shifts for different subsets of anatomical components, revealing a mosaic of adaptive landscapes for the parts of the body that drive body shape diversification in Pelagiaria.
