Adaptive Significance of Circadian Timing Systems in Wild, Free-Living Chipmunks

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9603878 DeCoursey Circadian pacemakers are presumed to be highly adaptive for survival and for genetic fitness of organisms since they play a role in diverse daily physiological and behavioral functions of nearly all animals. No direct test has been made, however, to assess the survival value of circadian pacemakers in wild species, primarily due to the technical difficulties involved. The object of this project is to use a favorable rodent circadian model to test the importance of the primary mammalian circadian pacemaker, the suprachiasmatic nuclei (SCN). The rationale of the research is to surgically create clockless, arrhythmic cohorts of a wild population by SCN lesioning, then compare and control and clockless groups. The study system will be the chipmunks of a southern Appalachian wilderness population at Mountain Lake Biological Research Station, Pembroke, Virginia. A year-long pilot study has demonstrated the feasibility of lesioning the SCN of wild-caught individuals, reintroducing them back into their burrows, and then documenting selected measures of fitness by periodic trapping censuses, daily visual observations, and tracking of radiotransmitter-collared animals. In the proposed study, all chipmunks of a 4-hectare grid will be marked by permanent ear tags and colored bead necklaces for visual observation. Twenty SCN-lesioned, 20 sham-lesioned, and 24 intact control animals will then be radiocollared and followed intensely for a two-year period; measures of fitness will include daily activity patterns, mortality, feeding success as evidenced by body weight, den and core territory defense, reproductive success, and hibernation behavior. In parallel with these free-living individuals, 5 control chipmunks and 5 SCN-lesioned chipmunkds will be monitored by radiotelemetry during the winter months from November to April in an outdoor Hibernaculum facility to obtain additional information on hibernation during the time that wild chipmunks are largely inactive underground and di fficult to monitor.