The biogenic amines serotonin (5-HT) and octopamine (OA) have many roles in neurological systems in decapod crustaceans influencing processes as diverse as sensitivity of individual sensory neurons and agonistic behaviours. I examined aspects of the aminergic system in the squat lobster Munida quadrispina (Anomura, Galatheidae) and compared my results with data on aminergic systems and behaviours in more extensively studied species. M. quadrispina has a complex set of agonistic behaviours, and in comparisons with crayfish and lobster behaviour one major difference stands out: squat lobsters do not normally fight. Injecting carefully controlled doses of 5-HT induces M. quadrispina to perform stereotypical aggressive behaviours in the absence of any additional stimulation, and animals under the influence of injected 5-HT will fight. Animals under the influence of injected OA are much more likely to initiate escape responses to a standardized stimulus than are untreated animals, and assume, under certain circumstances, a submissive stance in the absence of additional external stimulation. The distributions of serotonergic and octopaminergic neurons in M. quadrispina are overall fairly similar to those of crayfish, lobsters, and crabs. However, several important differences, such as a lack of unpaired medial serontonergic neurons and far fewer octopaminergic “crotch” cells in M. quadrispina than in lobsters may relate to functional differences in the aminergic systems and other systems influenced by the amines. The pereiopod depressor muscles lift the body of the animal above the substrate and, therefore, are important in aggressive, and other behaviours. In M. quadrispina, as in all decapods, the depressor muscle and its antagonist, the levator muscle, are composed of multiple anatomically distinct heads. Most published studies have treated the depressor muscle as a single functional unit, despite documented differences in the population of depressor excitatory motor neurons. In M. quadrispina, each head has individualistic patterns of excitatory innervation, and the heads are activated differentially during walking and maintained stance. These differences reveal a functional subdivision among the heads of the depressor muscle, with different combinations of heads responsible for movement of the leg, stance maintenance, and joint tension. Injecting 5-HT into freely moving animals increases the excitatory input to all of the heads of the depressor muscle, whereas injecting OA decreases excitatory input. / Graduate

Natural cycles of environmental variability and long-term deoxygenation in the ocean impose oxygen deficiency (hypoxia) on marine communities. My research exploits a naturally occurring hypoxia cycle in Saanich Inlet, British Columbia, Canada where I combined spatial surveys with remotely operated vehicles, ecological time-series from the subsea cabled observatory VENUS, and lab-based respirometry experiments to examine the influence of seasonally variable oxygen conditions on epibenthic communities. In situ oxygen thresholds established for dozens of fish and invertebrate species in this system show they naturally occur in lower oxygen levels than what general lethal and sublethal thresholds would predict. Expansion of hypoxic waters induced a loss of community structure which was previously characterized by disjunct distributions among species. Communities in variable hypoxia also have scale-dependent structure across a range of time scales but are primarily synchronized to a seasonal oscillation between two phases. Time-series revealed timing of diurnal movement in the slender sole Lyopsetta exilis and reproductive behavior of squat lobster Munida quadrispina in the hypoxia cycle. Hypoxia-induced mortality of sessile species slowed the rate of community recovery after deoxygenation. The 10-year oxygen time-series from VENUS, revealed a significant increase in the annual low-oxygen period in Saanich Inlet and that deoxygenation has occurred in this system since 2006. Differences in the critical oxygen thresholds (O2crit) and standard metabolic rates of key species (spot prawn Pandalus platyceros, slender sole, and squat lobster) determined the lowest in situ oxygen at which populations occurred and explained disproportionate shifts in distributions and community respiration. Finally, a meta-analysis on global O2crit reported for crustaceans showed that hypoxia tolerance differs among major ocean basins. Long-term trends of deoxygenation suggest a future regime shift may occur when the duration at which a system remains below critical oxygen levels exceeds the time needed for communities to recover. Species-specific traits will determine the critical threshold and the nature of the community response in systems influenced by variable states of oxygen deficiency. However, oceanographic and evolutionary history provides context when determining the regional response of benthic communities influenced by rapidly changing environments. / Graduate / 0329 / 0416 / 0433 / jwfchu@gmail.com