TY - JOUR TI - Bichir external gills arise via heterochronic shift that accelerates hyoid arch development AU - Stundl, Jan AU - Pospisilova, Anna AU - Jandzik, David AU - Fabian, Peter AU - Dobiasova, Barbora AU - Minarik, Martin AU - Metscher, Brian D AU - Soukup, Vladimir AU - Cerny, Robert A2 - Whitfield, Tanya T A2 - Tautz, Diethard A2 - Gillis, Andrew A2 - Ahlberg, Per E VL - 8 PY - 2019 DA - 2019/03/26 SP - e43531 C1 - eLife 2019;8:e43531 DO - 10.7554/eLife.43531 UR - https://doi.org/10.7554/eLife.43531 AB - In most vertebrates, pharyngeal arches form in a stereotypic anterior-to-posterior progression. To gain insight into the mechanisms underlying evolutionary changes in pharyngeal arch development, here we investigate embryos and larvae of bichirs. Bichirs represent the earliest diverged living group of ray-finned fishes, and possess intriguing traits otherwise typical for lobe-finned fishes such as ventral paired lungs and larval external gills. In bichir embryos, we find that the anteroposterior way of formation of cranial segments is modified by the unique acceleration of the entire hyoid arch segment, with earlier and orchestrated development of the endodermal, mesodermal, and neural crest tissues. This major heterochronic shift in the anteroposterior developmental sequence enables early appearance of the external gills that represent key breathing organs of bichir free-living embryos and early larvae. Bichirs thus stay as unique models for understanding developmental mechanisms facilitating increased breathing capacity. KW - bichir KW - pharynx KW - head KW - breathing KW - external gills JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -