Areas of Research
The major research focus in the Hadfield laboratory are the processes that occur when planktonic larvae of diverse marine invertebrate animals settle to the benthos and undergo the complex developmental processes of metamorphosis. Larvae of different species are known to respond to either surface-bound or, more rarely, dissolved cues to settlement and metamorphosis. We investigate these environmental cues in terms of the developmental processes that they induce; the stimulatory cues are thus investigated as chemical ligands that interact with the outer surfaces of larvae. This interaction produces a cascade of behavioral and morphogenetic processes, which result in the profound morphological and physiological alterations that are summarized as metamorphosis. Using especially a widely distributed tropical marine slug, Phestilla sibogae, and a common warm-water fouling organism, the tube worm Hydroides elegans, researchers in the lab collaborate to study the nature of the external cues, the sites of their perception, the nature of receptor mechanisms, the role of the nervous system in promulgating the morphogenetic signal, and the molecular events of metamorphic activation.
The role of marine-surface microbiomes in the recruitment of benthic invertebrates is now the major emphasis in our lab. The research has two major foci, the first being the genetic and structural identification of biofilm-bacterial mechanisms that specifically induce settlement of larvae of Hydroides elegans. A number of biofilm bacteria have been isolated to single-species culture allowing both quantitative and qualitative investigations. Employing transposon mutagenesis, we have created non-inductive mutant strains of the bacterium Pseudoalteromonas luteoviolacea and examined the transposon insertion sites to identify sets of ORFs responsible for coding induction factors. This led to the recognition of gene sets derived from phage-tail assemblages that produce arrays of type IV bacteriocins involved in the process of metamorphic stimulation in the worm larvae. Comparative studies are now underway with other inductive bacterial species in an effort to recognize general pathways among biofilm bacteria. In addition, the Hadfield lab group has undertaken metagenomic analyse of complex biofilms from different marine habitats with a goal of understanding the roles(s) of surface bacteria in determining the assemblages of benthic invertebrates living in the different habitats. In this effort, the group is studying the settlement biology of polychaete worms, corals, sponges, molluscs and other benthic invertebrates.
A second research area in the Hadfield lab is the conservation biology of a large group of tree snails unique to Hawaiʻi (family Achatinellidae). This effort led to the establishment of a captive-rearing facility where many species of endemic Hawaiian tree snails have been propagated in a setting free of the introduced predators responsible for the extinction of many of the endemic snails. Current research efforts focus on genetically defining populations of the tree-snail species that are adapted to differing ecological conditions across their ranges, as well as to the impacts of inbreeding on the survival of the snails. An outgrowth of this effort, has been studies of the partulid tree snails of the Mariana Islands, which are also endangered.