TILDEN, Andrea R.; CRANE , Meredith J.; CARY, Greg A.; PFEIFFER, Aubris L.; SHANAHAN, Kearney J.; Colby College; Colby College; Colby College; Colby College; Colby College: Influence of melatonin on locomotion and metabolic responses to stress in the fiddler crab Uca pugilator

Melatonin (MEL) influences locomotor activity in crustaceans, an effect that may be partly mediated by the enhanced release of neurotransmitter at the neuromuscular junction. This influence may be either excitatory or inhibitory, depending on the timing of injection relative to the phase of activity of the animal. Furthermore, MEL affects hemolymph glucose and lactate levels in a manner that is primarily independent of eyestalk factors such as CHH. Crabs acclimated to a 12L:12D photoperiod and 6L:6H:6L:6H tidal cycle were injected with MEL or saline at low tides (active phase) or high tides (inactive phase) and activity was monitored for three hours after injection. Melatonin had significant activity-enhancing effects during low tides, with a much smaller effect at high tides. MEL-treated crabs had lower glucose and lactate levels post-exercise but not post-osmotic stress.