11-rhythms%20%26%20seasonal%20breeding

11-rhythms%20%26%20seasonal%20breeding - Biological rhythms...

Info icon This preview shows pages 1–13. Sign up to view the full content.

View Full Document Right Arrow Icon
Biological rhythms and seasonal reproduction.
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Many species breed only at certain times of year – in order to give birth when ample food is available Breed during the summer Stop breeding when days get short in fall Spontaneous recovery in the spring the summer Hamsters:
Image of page 2
Quite a few seasonal rhythms are cued by photoperiod (day length), because photoperiod is the single most reliable environmental index of seasonal change. Days are longer in the summer than in the winter, and animals can detect these differences in photoperiod. Maine NC Peru The further you live from the equator, the greater the difference between summer and winter.
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Reproduction Before artificial lighting Energy balance Some species fatten in preparation for winter, others lose weight Depression – seasonal affective disorder. Some seasonal rhythms cued by photoperiod (day length): – maybe humans, too.
Image of page 4
Animals use circadian rhythms to keep track of day length. (circa = around, dies = day) Level of some physiological variable τ ( The two important parts of any rhythm are the amplitude (how much it changes) and the period (time required for a full cycle, τ ). For circadian rhythms, τ ≈ 24 hours.
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
They are approximately ( not exactly ) 24 hours in length, τ ≈ 24 hr. Properties of circadian rhythms: They are endogenous – generated from within the animal – not by external events.
Image of page 6
DAY NIGHT Measuring daily activity patterns in hamsters. Hamsters are nocturnal active at night. Animals that are active during the day are diurnal .
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
If running wheel activity reflects a circadian rhythm, then it should persist in constant conditions. If running wheel activity reflects a circadian rhythm, then the period should be roughly, but not exactly , 24 hours. constant darkness And it does. And it is. τ > 24 τ = 24 constant conditions day & night
Image of page 8
Another example: Resetting the light-dark cycle phase-shifts the running rhythm Reentrainment Activity free runs in constant conditions, and B is always close to 24 hr, e.g ., 23.9 < B >24.1 In constant conditions, activity free-runs and τ is always close to 24 hr, e.g ., 23.9 < τ >24.1 τ >24.1
Image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Humans have daily rhythms, too. And some of them are circadian.
Image of page 10
So where is it? It turns out that we have little clocks all over our bodies, but the biggie (the master clock) is in the suprachiasmatic nucleus (SCN) of the hypo- thalamus. OK we have this internal endogenous clock . . .
Image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
What’s the evidence that the SCN is the master clock? 1. If you lesion the SCN, animals become arrhythmic. They run at all different times of day with no organized pattern.
Image of page 12
Image of page 13
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern