Animal Photoperiodism & Circannual Rhythms PDF

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose ot...

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose other than to study for BSci 3230. Thanks, Carl Johnson  BSci 3230 Animal Photoperiodism & Circannual Rhythms Annual cycles of photoperiod (day/nightlength) Evidence that a circadian system measures daylength: a Photo- Periodic Time Measurement (PPTM) Melatonin as a PPTM signal Circannual cycles What about humans? Annual Hibernation Annual Migration Seasonal diapause: phase of suspended development Spring phenotype Fall phenotype  Photoperiodism was first reported in plants Tobacco is usually a "long-day" or a "day-neutral” plant day/night length Short-day plant Long-day plant Photoperiodism was first reported in plants Tobacco cultivar “Maryland Mammoth” (a spontaneous mutant) Flowering Short day (7 h L) Long day (14 – 15 h L) “Winter” “Early summer” W.Garner and H.Allard (1920) J. Agri. Res. 18:553 “Effect of the Relative Length of Day and Night and Other Factors of the Environment on Growth and Reproduction in Plants”  Photoperiodism was first reported in plants W. Garner and H. Allard (1920) J. Agri. Res. 18:553 “Effect of the Relative Length of Day and Night and Other Factors of the Environment on Growth and Reproduction in Plants”  Building a Seasonal Clock Yosemite Valley, California To cope with the increased energetic demands and diminished resources of winter, organisms have evolved behaviors and physiology to conserve energy, e.g.: hibernation, increased fur), avoid detection (e.g., coloration), time their reproduction (to favor the survival of offspring), or provide for escape (migration)  Tracking the Seasons Coloration Reproduction Summer Winter Soay sheep (Ovis Ptarmigan aries), gestation 150 (Lagopus muta) days (short day breeder) Snowshoe hare (Lepus americanus) Siberian hamster, gestation 21 days (long day breeder) Siberian hamster (Phodopus sungorus) movie courtesy of Frank Scherbarth Prof. Irwin Zucker  Tracking the Seasons Many animals (and plants) regulate their reproduction and physiology in a seasonal manner and use their circadian clock to measure day-length and trigger seasonal responses.  Tracking the Seasons In seasonally breeding animals, gestation time determines the season of breeding: sheep/deer in autumn, small rodents/birds in spring.  Tracking the Seasons Reproduction The onset of reproductive behavior is often controlled seasonally: e.g., flowering in plants and reproduction in animals. Not only behavior, but also reproductive organs are often seasonally controlled House sparrow  Biological Clocks are adaptations to environment cycles caused by living on a rotating, orbiting, and tilted planet. Photoperiodism – the earth’s tilted axis relative to its orbit around the sun ensures that there is an annual rhythm of daylength that creates the seasons. Photoperiod = daylength/nightlength LD 24:0 LD 0:24 LD 18:6 LD 6:18 LD 14:10 LD 10:14 LD 12:12 LD 12:12 LD 10:14 LD 14:10 LD 6:18 LD 18:6 LD 0:24 LD 24:0 The change of day length (photoperiod) is the best predictor of annual phase; seasonal changes in food availability and temperature are less accurate. Latitude impacts the annual cycle of day length  Photoperiodic Time Measurement (PPTM) long-day short-day percent response response response long-day vs. short-day response ”critical photoperiod” Two formal models Hourglass Model Circadian Model Threshold Sensitive Phase Short days Long days Some product accumulates in Circadian system is sensitive proportion to length of night to light at certain phases  Photoperiodic Time Measurement (PPTM) Scotophil or Photoinducible Phase or Photosensitive Phase The circadian model was first proposed by Erwin Bünning in the 1930s and is therefore called “Bünning’s Hypothesis” Erwin Bünning (1906 – 1990)  Photoperiodic Time Measurement (PPTM) Scotophil or Photoinducible Phase or Photosensitive Phase The circadian model was first proposed by Erwin Bünning in the 1930s and is photoinducible phase NOT illuminated therefore called “Bünning’s Hypothesis” Bünning’s Hypothesis is now usually referred to as the “External photoinducible phase illuminated Coincidence Model” for photoperiodism Erwin Bünning (1906 – 1990)  Photoperiodic Time Measurement (PPTM) Two formal models Hourglass Model Circadian Model Threshold Sensitive Phase Short days Long days Some product accumulates in Circadian system is sensitive proportion to length of night to light at certain phases Both Bünning’s Hypothesis and the Hourglass Model can explain how we get one response in short days and a different response in long days, so how can we test which one is correct?  Photoperiodic Time Measurement (PPTM) Two formal models Hourglass Model Circadian Model Threshold Sensitive Phase Short days Long days Some product accumulates in Circadian system is sensitive proportion to length of night to light at certain phases Night interruption experiment for a long-day response: LD 16:8 (long day) + response LD 8:16 (short day) no response LD 8:16 (interrupted) + response Night-interrupted photoperiods are interpreted as a long day  Photoperiodic Time Measurement (PPTM) If “diapause” is the regulated endpoint, what kind of a response is this? Note: LD 6:18 is inductive Pieris brassicae the large white cabbage butterfly One interpretation of the night- Can be interpreted as interruption experiment: it is the “asymmetric” skeleton duration of the night that is being photoperiods measured, not the ”day-length.”  Photoperiodic Time Measurement (PPTM) short-day response brief light pulses during the night long-day response brief light pulses during the night Is the night-interruption result consistent with the “hourglass model?” With the “circadian model?”  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment control: only one 8-h pulse Birds were given two 8-hour light pulses with various intervals of darkness between the light pulses. Is this a short- day or a long-day response? Can this result be interpreted in terms of the hourglass model?  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment control: only one 8-h pulse Birds were given two 8-hour light pulses with various intervals of darkness between the light pulses. Is this a short- day or a long-day response? Can this result be interpreted in terms of the circadian model?  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment Birds were given two 8-hour light pulses with various intervals of darkness between the light pulses. Is this a short- day or a long-day response? Can this result be interpreted in terms of the circadian model?  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment critical PP LONG DAYS is ~ 12 h 12-14 mm, 1.5 – 2.0 g 3-6 mm, 0.1 – 0.5 g SHORT DAYS  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the Nanda-Hamner Resonance Experiment Initial (T=24) (T=36) condition controls: LD14:10 Resonance Cycles (T=48) (T=60) Resonance Cycles LD 6:18 = T-cycle  Photoperiodic Time Measurement (PPTM) Test of the “circadian model:” the T-cycle Experiment Can this result be interpreted in terms of the “hourglass model?” Why or why not? What about the ”circadian model?” Why or why not?  Photoperiodic Time Measurement (PPTM) and Melatonin Is pineal melatonin production involved in PTM ? Melatonin levels in blood are high at night in all species. “The hormone of darkness” - clock-controlled - suppressed by light  Photoperiodic Time Measurement (PPTM) and Melatonin Is pineal melatonin production involved in PTM ? Melatonin levels in blood are high at night in all species. In multiple species, short the melatonin days profile is different long between long days days and short days short Is this relevant? days And if so, what is long the relevant days feature(s) of the melatonin profile? duration? short days phasing? long or what? days  Photoperiodic Time Measurement (PPTM) and Melatonin Is pineal melatonin production involved in PPTM ? Long day Syrian hamster Short day Modified from RY Moore, Fundamental Neuroscience 2nd edition (L. Squire et al., eds)  Photoperiodic Time Measurement (PPTM) and Melatonin Is pineal melatonin production involved in PTM ? Testes Weight: Long day Mean weight 3 grams Syrian hamster Short day Mean weight 0.5 grams Modified from RY Moore, Fundamental Neuroscience 2nd edition (L. Squire et al., eds) Photoperiodic Time Measurement (PPTM) and Melatonin LD 12:12 Experimental infusions of melatonin into pinealectomized hamsters Testicular size is a long-day (=short night) response in hamsters Melatonin mediates seasonal photoperiodic responses ! And, the duration of the melatonin signal is the critical feature  Anatomical Sites of Photoperiodic Time Measurement (PPTM) 1-s2.0-S0960982210015265-gr1_lrg.jpg 2,171×1,780 pixels 8/16/18, 4(04 PM PG pituitary gland SCN note  Anatomical Sites of Photoperiodic Time Measurement (PPTM) In birds and mammals, thyroxine and TSH appear to be involved in PPTM inactive pituitary gland active ec PPTM transduction in birds. Light information is detected by “deep brain photoreceptors” (OPN5 CSF-neurons) and transmitted to the pars tuberalis of the pituitary gland, inducing thyroid-stimulating hormone (TSH). TSH acts on the nearby ependymal cells (“ec”) to induce type 2 deiodinase (DIO2), which converts thyroxine (T4) to the active T3 form. This regulates GnRH secretion and hence gonadotropin (LH, FSH) secretion from the anterior pituitary gland. Yoshimura, Front. Neuroendocrinol. 34: 157–166 (2013)  Anatomical Sites of Photoperiodic Time Measurement (PPTM) 1-s2.0-S0960982210015265-gr1_lrg.jpg 2,171×1,780 pixels 8/16/18, 4(04 PM PG Tanycytes (ec) In mammals, light information is only perceived by the eye and transmitted to the pineal gland via the circadian pacemaker in the SCN. The duration of the pineal melatonin signal encodes the length of night and regulates TSH secretion in the pars tuberalis. Tanycytes = ependymal cells (“ec”) of the 3rd ventricle  Anatomical Sites of Photoperiodic Time Measurement (PPTM) In birds and mammals, thyroxine and TSH appear to be involved in PPTM Comparison of the photoperiodic signal transduction pathway in mammals vs. birds: In mammals, light information is only perceived by the eye and transmitted to the pineal gland via the circadian pacemaker in the SCN. The duration of the pineal melatonin signal encodes the length of night and regulates TSH secretion by the pars tuberalis. In contrast, in birds the light information received by deep brain photoreceptors induces TSH secretion from the pars tuberalis. Note that melatonin is not involved in the seasonal reproduction of birds. Note: pars tuberalis TSH is a master factor regulating seasonal reproduction in both birds and mammals (is there crosstalk with TSH that is regulating metabolism in general?). Yoshimura, Frontiers in Neuroendocrinology 34: 157–166 (2013)  Circannual Clocks 2. Circannual Clock Paul, Zucker, & Schwartz, Phil Trans R Soc B 363:341, 2008 Ÿ Does not require environmental input to generate seasonal/annual cycles Ÿ Cycles free-run in constant conditions (approx. 10-month period in many species) Ÿ Environment (predominantly day length) entrains the clock to a 12-month period Golden-mantled ground squirrel (Callospermophilus lateralis): Body Mass Ruby et al.,1998 LD 12:12 LD 14:10 6.5°C LL 23°C 6.5°C Years  Circannual Clocks Golden-mantled ground squirrels Laboratory-born, never experienced hibernation seasons or annual cycles, maintained in LD 12:12 at constant temperature. Black bars indicate hibernation; x indicates animal died Pengelley & Asmundson, Comp Biochem Physiol 32:155, 1970 Stonechats (passerine songbirds) Constant LD 12:12 photoperiod European (Saxicola rubicola) Siberian (Saxicola maurus) Helm, Schwabl, & Gwinner, J Exp Biol 212:1259, 2009  Annual Migrations & Sun-compass orientation in Butterflies Monarch butterflies provide a vivid example of the involvement of the circadian clock in migration and orientation. Starting in March, the eastern/northeastern populations migrate from the overwintering sites in central Mexico towards their summer grounds in southern Canada/northern United States, arriving in June/July. They start the return trip in September, arriving around November (~2,000 miles). No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least 4-5 generations are involved in the annual cycle. (We’ve already discussed HOW they orient, using the sun’s plane of UV polarization to detect the sun’s position, even on cloudy days.) (letztjährige generation = last year’s generation) Seasonal Cycles in a Migrating Bird’s Life Bartell & Moore, 2013  Annual Migrations & Sun-compass orientation in Birds Circannual Clocks? Starling “zugunruhe” = migratory restlessness body weight molt nocturnal activity  Circannual Clocks blackcap blackcap garden warbler garden warbler summer molts winter molts (black bars) (gray bars)  Circannual Clocks Circannual 12-month PP normal rhythms can be annually cycling entrained by the photoperiod annual changes (12 months) in photoperiod ! 6-month PP experimental half-year cycling molting photoperiod (6 months) constant LD 12:12 constant LD 12:12 photoperiod zugunruhe Various Annual Cycles in Humans Seasonal Affective Disorder (S.A.D.):  Annual Cycles in Humans: Conception Rates 1815-1827 1946-1958 1976-1982 1941-1949 1959-1965 1947-1973 1955-1966 1939-1952 The introduction of artificial lighting, temperature controlled housing, etc., into human culture has dramatically changed our life ! Roenneberg & Aschoff, J. Biol. Rhythms 1990  Food for Thought In the Nanda-Hamner experiment with white-crowned sparrows (LH hormone response), how would the data have looked if this had been a short-day response? What would the following result mean in the Nanda-Hamner protocol? % response Duration of darkness (h) in cycle If melatonin is involved in reproduction in lower mammals, what do you think about using it as a sleep aid in humans? Although there is little evidence for photoperiodism in humans, what are the factors in current human society that might invalidate a “no photoperiodism in humans” conclusion ?