Derby Lab Research
Research in the Laboratory of Charles Derby
Research field: Chemosensory Neurobiology and Behavior
- Crustaceans (lobsters, crabs, crayfish)
- Molluscs: Gastropods (sea hares), Cephalopods (squid, octopus, cuttlefish),
- Fish (flounder, bluehead wrasse, sea catfish)
- Molecular and Biochemical: Identifying bioactive molecules
- Cellular: Calcium Imaging and Electrophysiology
- Systems: Coding of stimuli by chemosensory systems
The focus of research in the Derby lab involves studies of the chemical senses. Our general objective is to understand how nervous systems are organized to allow animals to detect, identify, and respond to natural chemicals. We use crustaceans (lobsters, crabs, crayfish), mollusks (sea hares, cephalopods), and fish (sea catfish, wrasses, flounder) as model organisms. We are presently employing a variety of techniques to answer questions involving different levels of sensory systems, including molecular, immunocytochemical, anatomical, electrophysiological, and behavioral approaches.
RESEARCH PROJECTS INCLUDE THE FOLLOWING:
How do animals chemically defend themselves against predators?
- A diversity of marine molluscs, including sea hares (Aplysia spp.) and cephalopods (squid, octopus, cuttlefish) chemically defend themselves against predators such as crustaceans, anemones, and fish by releasing an ink. This ink has many chemicals that act through diverse and interesting mechanisms, including the following:
- Phagomimicry: creating a supernormal chemical attractant of itself, such that the predator attends to the phagomimic while the sea hare escapes.
- Chemical disruption: inactivating or disrupting in various ways the predator’s chemical senses, thus affecting its perception of potential prey.
- Deterrent chemicals: chemicals that are noxious or cause cell damage. For sea hares, these include products of escapin (an L-amino acid oxidase) that oxidizes L-lysine to form hydrogen peroxide, ammonia, and a variety of acids and other compounds), phycoerythrobilin, and others. For cephalopods, these include currently unidentified molecules mostly associated with melanin granules.
- Alarm cues: sea hares and cephalopods can respond to ink from neighbors with escape behavior, and some of these compounds have been identified.
We are exploring these and other mechanisms of the sea hare’s chemical defense, and how these defensive molecules may be used for human applications, using a diversity of experimental approaches.
Adult neurogenesis and the stem cell niche: How does the olfactory system stay functional in long-lived animals?
The olfactory organ of crustaceans is continually growing throughout the animal’s life. There is continuous turnover of olfactory receptor neurons in the antennule, with cell birth, maturation, and death occurring in less than one year. There is also continuous addition of new olfactory interneurons in the brain of adult crustaceans, and this neurogenesis occurs in a stem cell niche. We are examining the dynamics to these processes, using cell and molecular techniques, calcium imagining of odor responses, and other techniques.
How do crustaceans communicate through pheromones?
We are examining chemical communication in crustaceans. Blue crabs communicate reproductive status via pheromones. For example, when female crabs are ready to mate, they release signals in their urine that elicit courtship display behaviors and chemical signaling by males. We are searching for the bioactive molecules constituting this female sex pheromone. Another example that we are studying is social odors in spiny lobsters. Spiny lobsters are social animals that are socially attracted to each other via aggregation cues and that avoid damaged neighbors due to alarm cues in their blood. We are exploring the sensory biology of these behaviors, including identifying the molecules involved.
Why do crustaceans have such complex olfactory systems?
The olfactory organ of crustaceans – the first antenna or antennule – mediates many behaviors of crustaceans, including detection of sex pheromones, social cues, and food odors, orientation to those cues in odor plumes, discrimination of and learning about odors, and grooming of the antennule. Their olfactory organ has a rich diversity of sensors and at least two major pathways into the brain, yet we know very little about how this diversity enables the vast behavioral repertoire of crustaceans. Thus, we are exploring the functional organization of this chemosensory system, with behavioral to molecular approaches, and from a broadly comparative perspective.
What is the value of marine reserves to spiny lobsters?
Marine reserves are being established around Florida and the Caribbean with the notion that they will protect and enhance populations of animals including commercially important species such as spiny lobsters. To evaluate the impact of marine reserves, we need to know the population structure of target species, including the animals’ ages. This is easily done on fish, using otoliths or scales. For crustaceans, this is not so easy – the only established and reliable method is by quantification of lipofuscin. Lipofuscin is a product of lipid metabolism that accumulates in tissues proportionally to the physiological age of animals. Lipofuscin levels are most accurately measured in tissues using light microscopy (lipofuscin autofluoresces, so it can be visualized as glowing granules), and the best tissue for quantification of lipofuscin in crustaceans is the brain. The age of a lobster can be assigned by quantifying its lipofuscin and comparing this to lipofuscin levels in a population of animals of known age. Together with scientists at the Florida Marine Research Institute, we have shown that this technique works for spiny lobsters, we are now using it to evaluate the effect of the Dry Tortugas and Western Sambos Reserves on lobsters by comparing their population structure inside and outside of these reserves.