My central research focus is based on the evolution and systematics of actinopterygian fishes. Specifically, I am interested in evolutionary change in tandem with the ontogenetic transformation of complex morphological structures and the role they play in the vast diversity of actinopterygian fishes. Anatomists in the 19th century, such as Ernst Haeckel and Karl Ernst von Baer determined that the ontogeny of organisms provides information from their evolutionary history (recapitulation). In many cases this information provides the most convincing approach for understanding evolutionary trajectories. To incorporate this approach into my own research, I use standard methods, such as histology, as well as clearing and staining, but also advanced techniques, such as whole-mount immunohistochemistry, confocal microscopy, and X-ray computed micro-tomography (CT-scans) of soft tissues.
Rosaura to Gigantura
With G. David Johnson, the Smithsonian Institution, National Museum of Natural History
The family Giganturidae comprises two species, Gigantura indica and G. chuni, which undergo one of the most drastic developmental transformations known among teleostean fishes. The transformation is so radical that in 1954, Tucker described an 8.4 mm giganturid larva as a different genus and species, Rosaura rotunda and placed it in a separate family, Rosauridae. The relationship between Rosaura and Gigantura remained undiscovered until the mid-1960’s. Throughout the developmental journey to the adult stage, the larvae change dramatically. In addition to striking external changes in body shape and eye orientation, the jaws, gill arches, and pectoral girdle undergo radical reductions as well as topographic and structural changes that make them challenging to identify and homologize. Robert K. Johnson, well known for his work on aulopiform fishes, intended to describe the osteological transformation of Gigantura, but he abandoned the project prior to his untimely death. Inspired in part by specimens that Dave and I identified at a larval fish workshop in Tokyo we decided to revive R.K. Johnson’s planned project. We have located most of the transforming specimens R.K. Johnson pictured in the 1991 DANA report at their respective institutions. In a second step, after describing the adult morphology of giganturids (Konstantinidis & Johnson 2017), we are in the process to describe the incredible anatomical transition from the larval to the adult stage.
Pelvic fin development in triggerfishes of the family Balistidae
With James C. Tyler, the Smithsonian Institution, National Museum of Natural History, and Andrew Chione, Oregon State Univ.
Osteology of Parabrotula plagiophthalma
Eric J. Hilton, Virginia Institute of Marine Science, College of William and Mary, and Andrew Williston, Museum of Comparative Zoology, Harvard University
Parabrotulidae comprises two species of the genus Parabrotula and the monotypic Leucobrotula, and has been allied to aphyonids, zoarcids, and other groups. In Fishes of the World Nelson calls them a “family without a home.” These fishes are small (<50 mm TL) and eel-like, and inhabit the bathypelagic zone. We are analyzing the skeletal anatomy of P. plagiophthalma based on cleared and stained specimens and x-ray computed tomography of alcohol-stored specimens. The skeleton is highly reduced and the bones that are present are weakly ossified. The posttemporal and supracleithrum are thin rods of bone, (although the cleithrum is relatively massive and well ossified) and the chondral portion of the pectoral girdle is unossified. The dentary is the only tooth-bearing bone of the oral jaws and the vomer only variably has teeth. The ectopterygoid is extremely thin, and the pars autopalatina is entirely separate from the more posterior regions of the chondral suspensorium. The interopercle is broad anteriorly but tapers to a threadlike posterior region that broadly overlaps an equally thin subopercle. Most remarkably, the fifth ceratobranchials are represented only by a pair of small, weakly formed cartilages; it has not been determined if this is due to delayed development or secondary ontogenetic reduction. Among teleosts, the loss of ceratobranchial five is otherwise seen in only in some anguilliforms, in which it is an ontogenetic loss. These and other aspects of the morphology of Parabrotula will be discussed in a comparative framework.