Collaborative Research: RUI: Extraordinary circadian clocks in araneoid spiders: an integrative approach to understanding their evolutionary origins and underlying mechanisms

Circadian rhythms are daily rhythms of behavior, physiology, and cellular metabolism that are driven by molecular cycles of an internal biological clock. Internal clocks remain in sync with the earth’s 24-h day by making small adjustments to their own internal clock period. However, there are negative physiological consequences if the clock is forced to make large adjustments (e.g., jetlag) so most organisms’ clocks do not vary much from 24 hours. Surprisingly, a group of spider species possess clocks that differ from 24 hours by as much as 5 hours with no apparent consequences. In theory, these species should not exist! However, the spider system provides a unique opportunity to explore basic mechanisms of circadian clocks, particularly how organisms synchronize with their environment. This multi-institutional project is designed to understand: (1) the evolutionary changes in clock genes and circadian properties in spiders, (2) the limits and physiological consequences of synchronizing to the 24-h day, and (3) the fundamental molecular clockworks of spiders. Overall, this project will develop a new, and uniquely powerful, model system to understand circadian rhythms and, potentially, circadian illnesses. Circadian rhythms are conceptually accessible to students and this project will support rich opportunities for undergraduates in the Appalachian region to participate in research at all three institutions. Societal impacts of this project will include development of user-friendly, open-access applications for rigorous analyses of circadian data, annual public outreach events including nature/STEM programs for K-12 students as well as adults, and conducting original experiments in local high schools. Araneoid spider circadian rhythms are unlike most others found on Earth. They exhibit remarkably broad distributions of endogenous free-running periods (FRPs) both within and among species, including species with exceptionally short or long mean FRPs (17.8-29.1 hours). Rather than suffering negative consequences typically associated with dissonance between endogenous circadian period and the 24-hour day, survivorship experiments suggest that they are somehow released from these selective constraints. Using an integrative, multi-level approach, this project will exploit the apparent evolutionary shift in circadian clock system function between araneoid and non-araneoid spider species to identify changes in the clock mechanisms that enable these unusual araneoid clocks to exist. Using genomic or transcriptomic-scale data to estimate rates of evolutionary change in eight different chronobiological parameters for species spanning the diversity of spiders will enable reconstruction of ancestral states and pinpoint the timing of evolutionary shifts. Comparing survivorship among araneoid and non-araneoid species will determine if araneoid spiders truly have been released from the costs of entrainment to non-resonant light/dark cycles. Classic phase-shifting and phase-response curve experiments will probe differences in entrainment potential between araneoid and non-araneoid spiders. Comparing canonical clock gene expression amplitudes between araneoid and non-araneoid spiders and to established insect models will explore potential clock function differences. Comparing the functionality of the clock component CRY1 between araneoid and non-araneoid species will test for differences in light sensitivity of the circadian system. Using molecular, behavioral, and phylogenetic approaches, this project explores the extent and functional ramifications of circadian plasticity in wild clocks.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.