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Lecture 18

BIOLOGY 321 Lecture 18: Lecture 18

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Primate Sexuality 321 End of Female Sexuality Behavior Lecture: Evidence of peaks in sexual behavior and sexual desire during the days leading up to ovulation and peaking at ovulation I. Male Cycles a. Cycle of T and sperm is a lifetime cycle (see graph on slides) b. Testosterone peaks in mid gestation, goes to zero at birth, then postnatal peak when a few weeks old in baby boys i. Prenatal rise of T related to immunity later in life (organizational hormone??) c. At puberty there is a rise in testosterone to levels that plateau and then decrease starting at the mid 20s and continuing through life i. Mirrored by sperm production, only begins at puberty but then follows the T trend ii. However, men are still reproductively capable, whereas in female there would be compromises for the fetus d. Tradeoffs for health benefits and cost for testosterone e. Diurnal Androgen Secretion i. Throughout 24hr, in a squirrel monkey there are peaks and troughs of androgen production, but these are species specific ii. In humans, highest levels in the morning, lowest in evening iii. These peaks and troughs are important to know in controlling for variation between individuals that might be simply due to diurnal variations at different times of day f. Photoperiod effects on receptors in human pineal i. Seasonal breeders have singnificant seasonal changesseasonality generally not seen in greater apes ii.There is evidence of LH and FSH differences based on summer vs. winter (shown to be stat. signif. In a study from 1997) g. Seasonal Cycle: Androgens i. Testosterone and DHT have minimums in marchApril, then the most dramatic rise in June, peaking at 3x more in NovemberDecember ii. There is a lag, as sex actually increases in AugSeptember despite hormones increasing in June iii.This correlates with increases in births in April through August during perhaps when it is best to have children (most available resources) iv. In the study shown, births are timed when day lengths are on the rise, timed so they are weened when food is most plentiful v.In other species, precipitation dictates seasonalitybirth timed during wet season when vegetation and food available vi. Environmental control shown through cycles changing when environment is manipulated
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