Seasonal Adaptations of Siberian Hamsters. II. Pattern of Change in Day Length Controls Annual Testicular and Body Weight Rhythms1

Gorman, Michael R.; Zucker, Irving H.

doi:10.1095/biolreprod53.1.116

Cited by 98 publications

(102 citation statements)

References 32 publications

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“…Growth of the testes in Siberian hamsters is not affected by the increase in day length between the winter solstice and the vernal equinox (Gorman & Zucker 1995). The regrowth process is initiated endogenously by the interval timer, all other environmental factors being held constant.…”

Section: Annual Timekeeping Mechanismsmentioning

confidence: 99%

“…At and around the equator, changes in photoperiod are minimal at best, and other environmental cues may not occur at the correct time with respect to ultimate factors. For example, rainfall may occur too close to the (Gorman et al 2001;Zucker 2001;Gwinner 2003). However, the functional role of photoperiod differs for the two mechanisms.…”

Section: (C) Timers Versus Clocksmentioning

confidence: 99%

“…Subsequent exposure to short day lengths is then required to break refractoriness. It has been proposed that a critical day length exists that defines all shorter photoperiods as winter and all longer photoperiods as summer (reviewed in Gorman et al 2001). Relatively sharp inflection day lengths have been reported for several species (Gaston & Menaker 1967;Elliott 1976;Hoffmann 1982a;Rhodes 1989).…”

Section: (C) Timers Versus Clocksmentioning

confidence: 99%

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Tracking the seasons: the internal calendars of vertebrates

Paul

Zucker

Schwartz

2007

Phil. Trans. R. Soc. B

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175

152

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Animals have evolved many season-specific behavioural and physiological adaptations that allow them to both cope with and exploit the cyclic annual environment. Two classes of endogenous annual timekeeping mechanisms enable animals to track, anticipate and prepare for the seasons: a timer that measures an interval of several months and a clock that oscillates with a period of approximately a year. Here, we discuss the basic properties and biological substrates of these timekeeping mechanisms, as well as their reliance on, and encoding of environmental cues to accurately time seasonal events. While the separate classification of interval timers and circannual clocks has elucidated important differences in their underlying properties, comparative physiological investigations, especially those regarding seasonal prolactin secretions, hint at the possibility of common substrates.Keywords: seasonality; photoperiodism; circannual; interval timers While the Earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.Genesis 8: 22, King James Version (1611) As the Earth makes its yearly orbit around the Sun, the planet's 23.58 axial tilt leads to the cyclical environmental changes that we call the seasons. Recurrent challenges to the survival of organisms and their offspring arise with the dawning of each new season, and animals have evolved seasonally induced changes in phenotype that adapt them to these predictable events. For example, in many temperate environments, winter is generally characterized by severe decreases in ambient temperature and food availability, leading to increased energetic demands at a time when resources are diminished. Because energy requirements of female mammals typically increase markedly during lactation (Bronson 1989) and newly weaned offspring are particularly vulnerable to environmental perturbations (Hill 1992), raising offspring during this time of year is often futile. Thus, many temperate species have evolved winter-specific behaviours and physiology to conserve energy (e.g. hibernation, a more insulative pelage, huddling) or provide for escape (e.g. migration). Many species also increase the chances of offspring survival by timing their mating behaviours so that parturition occurs during energetically favourable times of year.

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Section: Annual Timekeeping Mechanismsmentioning

confidence: 99%

Section: (C) Timers Versus Clocksmentioning

confidence: 99%

Section: (C) Timers Versus Clocksmentioning

confidence: 99%

See 1 more Smart Citation

Tracking the seasons: the internal calendars of vertebrates

Paul

Zucker

Schwartz

2007

Phil. Trans. R. Soc. B

Self Cite

175

152

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show abstract

“…Testis size was estimated by measuring the length and width of the left testis through the abdominal skin while under light isoflurane anesthesia. This provides a measure of estimated testis volume (ETV), which is correlated with testis weight, circulating testosterone and spermatogenesis (Gorman and Zucker, 1995;Schlatt et al, 1995).…”

Section: Photoperiod Manipulationsmentioning

confidence: 99%

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Wen

Dhabhar

Prendergast

2007

Hormones and Behavior

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Siberian hamsters (Phodopus sungorus) exhibit reproductive and immunological responses to photoperiod. Short (<10-h light/day) days induce gonadal atrophy, increase leukocyte concentrations, and attenuate thermoregulatory and behavioral responses to infection. Whereas hamster reproductive responses to photoperiod are dependent on pineal melatonin secretion, the role of the pineal in short-day induced changes in immune function is not fully understood. To examine this, adult hamsters were pinealectomized (PINx) or sham-PINx, and transferred to short days (9-h light/day; SD) or kept in their natal long-day (15-h light/day; LD) photoperiod. Intact and PINx hamsters housed in LD maintained large testes over the next 12 weeks; sham-PINx hamsters exhibited gonadal regression in SD, and PINx abolished this effect. Among pineal-intact hamsters, blood samples revealed increases in leukocyte, lymphocyte, CD62L+ lymphocyte, and T cell counts in SD relative to LD; PINx did not affect leukocyte numbers in LD hamsters, but abolished the SD increase in these measures. Hamsters were then treated with bacterial lipopolysaccharide (LPS), which induced thermoregulatory (fever), behavioral (anorexia, reductions in nest building), and somatic (weight loss) sickness responses in all groups. Among pineal-intact hamsters, febrile and behavioral responses to LPS were attenuated in SD relative to LD. PINx did not affect sickness responses to LPS in LD hamsters, but abolished the ameliorating effects of SD on behavioral responses to LPS. Surprisingly, PINx failed to abolish the effect of SD on fever. In common with the reproductive system, PINx induces the LD phenotype in most aspects of the immune system. The pineal gland is required for photoperiodic regulation of circulating leukocytes and neural-immune interactions that mediate select aspects of sickness behaviors.

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“…Simpson et al 1982). Photorefractoriness in mid-winter initiates the recovery of reproductive function many weeks in advance of permissive (long) day lengths (Gorman & Zucker 1995a) and permits early spring breeding (Clarke 1981). Surprisingly, the issue of photorefractoriness has not been addressed with regard to immune function.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous ‘regression’ of enhanced immune function in a photoperiodic rodent Peromyscus maniculatus

Prendergast

Nelson

2001

Proc. R. Soc. Lond. B

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Short days inhibit reproduction and enhance immune function in deer mice (Peromyscus maniculatus). Their reproductive inhibition is sustained by an endogenous timing mechanism: after ca. 20 weeks in short days, reproductive photorefractoriness develops, followed by spontaneous recrudescence of the reproductive system. It is unknown whether analogous seasonal timing mechanisms regulate their immune function or whether enhanced immune function is sustained inde¢nitely under short days. In order to test this hypothesis, we housed adult male deer mice under long (16 h light day 71 ) or short (8 h light day 71 ) day conditions for 32 weeks or under long day conditions for 20 weeks followed by 12 weeks of short days. Mice under the long day conditions remained photostimulated over the 32 weeks, whereas mice housed under the short day conditions exhibited gonadal regression followed by photorefractoriness and spontaneous recrudescence. Mice transferred to short days at week 20 were reproductively photoregressed at week 32. Total splenocytes, relative splenic mass and mitogen-activated splenocyte proliferation were greater in those mice transferred to short days at week 20 than in those mice housed under either long or short day conditions for 32 consecutive weeks, and immune function in mice exposed to short days for 32 weeks was comparable with that of long day animals. These data suggest that short day enhancement of immune function is not inde¢nite. With prolonged (4 32 weeks) exposure to short days, several measures of immune function exhibit`spontaneous' regression, restoring long day-like immunocompetence. The results suggest that formal similarities and, possibly, common substrates exist among the photoperiodic timekeeping mechanisms that regulate seasonal transitions in reproductive and immune function.

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Seasonal Adaptations of Siberian Hamsters. II. Pattern of Change in Day Length Controls Annual Testicular and Body Weight Rhythms1

Cited by 98 publications

References 32 publications

Tracking the seasons: the internal calendars of vertebrates

Tracking the seasons: the internal calendars of vertebrates

Pineal-dependent and -independent effects of photoperiod on immune function in Siberian hamsters (Phodopus sungorus)

Spontaneous ‘regression’ of enhanced immune function in a photoperiodic rodent Peromyscus maniculatus

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