The overall goals of this project are: 1) to use the horseshoe crab, Limulus polyphemus, as a model system for investigating the endogenous processes that give rise to circadian and circatidal rhythms and; 2) to determine how both types of rhythms are coordinated with environmental stimuli and annual reproductive cycles. The horseshoe crab is an excellent subject for these studies because in the laboratory they exhibit clear, reproducible tidal and circadian rhythms that can be entrained to environmental stimuli (such as day/night and tidal changes). Further, in the field, their large size and mobility make it possible to quantify their movements with ultrasonic telemetry. Moreover, the fact that they exhibit a distinct intertidal mating behavior in the spring and summer that is synchronized to the high tides makes it possible to investigate how these behavioral rhythms are differentially expressed on a seasonal basis. Two methods will be used to collect locomotor activity: ultrasonic telemetry in the field and "running wheels" in the laboratory. Ultrasonic telemetry will be used to quantify the biological rhythms of freely behaving Limulus in their natural habitat and determine when each type of rhythm is expressed in order to gain insight into what environmental cues may help to synchronize each of the rhythms. Running wheels will be used to test the role of different stimuli in synchronizing circatidal vs. circadian rhythms and to test whether these rhythms are controlled by a single endogenous clock or by two (or more) separate endogenous clocks. One of the broader impacts of this study will be to directly address a central issue in the field of biological rhythms of intertidal marine species: whether behavioral rhythms are controlled by circalunidian oscillators or by both circadian and circatidal oscillators.
Broader Impacts: This study will have a number of additional broader impacts: 1) This is an RUI grant and it will significantly enhance the training of undergraduate students in the sciences, especially at Plymouth State, an institution that educates many of the K-12 educators in the state. 2) Importantly, the study proposes to investigate the internal and external factors that affect Limulus behavior over the course of a year and especially during its mating season. Since many recent studies have suggested that this species is in decline over most, if not all, of its' range, a better understanding of the factors that underlie this commercially and ecologically important species' mating behavior is crucial. 3) In addition, this study will enhance our understanding of how internal clocks and environmental influences combine to influence the expression of certain behaviors, and how these behaviors are differentially manifested in the lab versus the field. 4) Results from this study will also help to link information from the large body of work done on Limulus visual sensitivity to overall behavior in this species. 5) Additionally, this proposal directly addresses an important overall issue in the field of chronobiology, the mechanisms by which animals may control multiple physiological and behavioral processes.
