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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Simulated natural day lengths synchronize seasonal rhythms of asynchronously born male Siberian hamsters

¹Departments of Integrative Biology and ²Psychology, University of California, Berkeley, California; and ³Molecular and Integrative Physiological Sciences Program, Harvard School of Public Health, Boston, Massachusetts

Submitted 28 February 2007 ; accepted in final form 20 March 2007

Photoperiodism research has relied on static day lengths and abrupt transitions between long and short days to characterize the signals that drive seasonal rhythms. To identify ecologically relevant critical day lengths and to test the extent to which naturally changing day lengths synchronize important developmental events, we monitored nine cohorts of male Siberian hamsters (Phodopus sungorus) born every 2 wk from 4 wk before to 12 wk after the summer solstice in a simulated natural photoperiod (SNP). SNP hamsters born from 4 wk before to 2 wk after the solstice underwent rapid somatic and gonadal growth; among those born 4–6 wk after the solstice, some delayed puberty by many weeks, whereas others manifested early puberty. Hamsters born eight or more weeks after the solstice failed to undergo early testicular development. The transition to delayed development occurred at long day lengths, which induce early puberty when presented as static photoperiods. The first animals to delay puberty may do so predominantly on the basis of postnatal decreases in day length, whereas in later cohorts, a comparison of postnatal day length to gestational day length may contribute to arrested development. Despite differences in timing of birth and timing of puberty, autumn gonadal regression and spring gonadal and somatic growth occurred at similar calendar dates in all cohorts. Incrementally changing photoperiods exert a strong organizing effect on seasonal rhythms by providing hamsters with a richer source of environmental timing cues than are available in simple static day lengths.

Phodopus sungorus; simulated natural photoperiod; puberty; interval timer; critical day length

This article has been cited by other articles:

				M. J. Paul, N. T. George, I. Zucker, and M. P. Butler Photoperiodic and hormonal influences on fur density and regrowth in two hamster species Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2007; 293(6): R2363 - R2369. [Abstract] [Full Text] [PDF]