Michael G. Hadfield
Professor Emeritus, Pacific Biosciences Research Center
Larval Settlement and Metamorphosis; Conservation and Evolutionary Biology of Hawaiian Tree Snails
Henke 336/Kewalo Lab 214
We take a very broad approach to studies of settlement and metamorphosis of marine invertebrate animals. Metamorphosis in larvae of many invertebrates depends on very specific external chemical signals. Our studies include investigation of the chemical nature of a small metabolite from prey coral that induces settlement and metamorphosis in the sea slug Phestilla sibogae and of a complex substance from bacterial films that induces metamorphosis in the small fouling worm Hydroides elegans. We have extensively investigated settlement-signal transduction mechanisms in these larvae, as well as the roles of de novo transcription events following induction. We are interested in the genetics of both bacteria and larval populations in determining settlement in larval H. elegans. The latter work has led us to a major interest on the composition of marine biofilms, and thus on the interactions between marine microorganisms and developing marine animals at the time of larval recruitment. Finally, together with a collaborator from the University of California, we are studying the responses of invertebrate larvae with living benthic communities, both coral reefs and biofouling communities.This effort includes extensive field studies, research in very large and very small flumes, and extensive micro-videography of larvae at the point of settlement.
Among the spectacular endemic evolutionary radiations for which Hawai'i is famous is that of the terrestrial and arboreal snails. These snails are famous for both their high rates of speciation and, more recently, their disastrously high extinction rates. We study, in the field and the laboratory, the demography and conservation biology of a single family of endemic Hawaiian snails, the Achatinellidae. These snails have suffered from habitat alteration and outright destruction and from introduced predators. Our field studies provide models for determining demographic patterns and analyzing causes of mortality of terrestrial invertebrates in their natural habitat, and they reveal much about the mechanisms of evolution in these snails. Our captive propagation effort now includes eight Achatinella species. Currently we are studying microsatellite DNA sequences to compare genetic identities of individual snails, analyze the degree of inbreeding in very small, remnant field populations, and improve breeding plans for captive-rearing.
Huang, Y., C. Callahan and M. G. Hadfield. 2012. Recruitment in the sea: bacterial genes required for inducing larval settlement in a marine worm. Scientific Reports 2:228 | DOI: 10.1038/srep00228.
Pelep, P. O. and M. G. Hadfield. 2011. The status of the endemic snails of the genus Partula (Gastropoda: Partulidae) on Pohnpei, Federated States of Micronesia. Micronesica 41(2):253–262.
Ruiz-Jones, G. J. and M. G. Hadfield. 2011. The loss of sensory elements in the apical sensory organ during metamorphosis in the nudibranch Phestilla sibogae. Biol. Bull. 22:39-46.