Global phylogenetic relationships of Butorides herons (Aves: Ardeidae) reveal the evolutionary history and taxonomic status of the Galápagos Lava Heron

AbstractGlobally-distributed genera and species provide important opportunities to understand divergence and dispersal across and within continents. Butorides herons (Aves: Ardeidae), including the highly variable Striated Heron (B. striata) and Green Heron (B. virescens), are two species similar in their ecology and plumage. B. striata occurs world-wide, is concentrated in tropical regions, and has highly variable plumage that has led to the classification of at least 29 subspecies. One of the more distinctive is the dark-plumaged Lava Heron of the Galápagos archipelago (B. s. sundevalli). This taxon has been treated as either a full species or a subspecies, but its taxonomic status has been hindered by the lack of genetic assessments. Here, we present a genus-level phylogeny of Butorides herons based on thousands of ultraconserved elements (UCEs). We also investigate morphological variation collected from 308 live and preserved specimens across its broad geographic range. Our genetic results suggest a biogeographic split between Old and New World Butorides herons as well as significant phylogenetic and morphological structure within the Americas, requiring subsequent taxonomic reassessment. Contrary to earlier taxonomic assumptions, Old World Butorides herons are not the closest relative to South American Butorides, and Lava Herons were recovered as a monophyletic lineage sister to Green Herons. Morphological data also highlights the Lava Heron’s evolutionary history as they possess unique bills that are possibly adapted to their insular diet behavior. Genetic and morphometric evidence adds to our understanding of Butorides and supports a reassessment of the B. striata label.