Chapter 11: Reproductive Behaviors


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Sexual behavior and hormones, mating behavior, and sexual orientation.

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Chapter 11: Reproductive Behaviors

  1. 1. Reproductive Behavior
  2. 2. The Effects of Sex Hormones Hormones Chemicals secreted by the glands & carried by the blood to other organs whose activity they influence Endocrine Glands Hormones coordinate long-lasting changes in many parts of the body
  3. 3. Classes of Hormones <ul><li>Protein & Peptide Hormones </li></ul><ul><li>Composed of chains of amino acids </li></ul><ul><li>Proteins are longer chains; peptides are shorter chains </li></ul><ul><li>Attach to receptors on cell membranes where they activate 2 nd messengers within the cell </li></ul><ul><li>Steroid Hormones </li></ul><ul><li>Cortisol & corticosterone </li></ul><ul><li>Bind to membrane receptors like protein or peptide hormones </li></ul><ul><li>Enter cells & attach to receptors in the cytoplasm, which then move to the nucleus where they determine gene expression </li></ul><ul><li>Sex Hormones </li></ul><ul><li>Androgens : testosterone </li></ul><ul><li>Estrogen : estradiol </li></ul><ul><li>Anabolic steroids : testosterone & other androgens, & synthetic chemicals derived from them </li></ul><ul><li>Sex-linked genes : genes activated by sex hormones </li></ul><ul><li>Other Hormones </li></ul><ul><li>Thyroid hormones : released by the thyroid gland containing iodine </li></ul><ul><li>Monoamine hormones : norepinephrine & dopamine </li></ul>
  4. 4. Control of Hormone Release <ul><li>Pituitary Gland </li></ul><ul><li>Called the “master gland” because its secretions influence other glands </li></ul><ul><li>Posterior Pituitary Gland </li></ul><ul><li>Releases oxytocin & vasopressin </li></ul><ul><li>Anterior Pituitary Gland </li></ul><ul><li>Synthesizes 6 hormones: </li></ul><ul><li>Adrenocorticotropic hormone (ACTH) </li></ul><ul><li>Thyroid-stimulating hormone (TSH) </li></ul><ul><li>Prolactin </li></ul><ul><li>Somatotropin or Growth hormone (GH) </li></ul><ul><li>Follicle-stimulating hormone (FSH) </li></ul><ul><li>Leutinizing hormone (LH) </li></ul>
  5. 5. Organizing Effects of Sex Hormones <ul><li>Organizing Effects </li></ul><ul><li>Occurs mainly during a sensitive stage of development </li></ul><ul><li>Determines whether the brain & body develop as a male or female </li></ul><ul><li>Activating Effects </li></ul><ul><li>Are temporary, happening only while a hormone is present </li></ul><ul><li>Can occur at any time in life </li></ul><ul><li>Sex Differences in the Gonads & Hypothalamus </li></ul><ul><li>Differentiation begins with the chromosomes </li></ul><ul><li>Female = XX & Male = XY </li></ul><ul><li>Gonads are the reproductive organs </li></ul><ul><li>In mammals, the gonads of males & females are identical early in prenatal development </li></ul><ul><li>SRY Gene </li></ul><ul><li>Gene on the Y chromosome responsible for causing the primitive gonads in males to become testes </li></ul><ul><li>Testes </li></ul><ul><li>Sperm-producing organs which also synthesize the androgens </li></ul><ul><li>Wolffian Ducts </li></ul><ul><li>Precursors of the male reproductive organs that develop into the seminal vesicles & the vas deferons after testosterone exposure during prenatal development </li></ul>
  6. 6. Organizing Effects of Sex Hormones <ul><li>M  llerian Inhibiting Hormone (MIH) </li></ul><ul><li>A peptide hormone that degenerates the M  llerian ducts in males </li></ul><ul><li>Testosterone also results in the development of the penis & scrotum </li></ul><ul><li>In females, primitive gonads become ovaries and her M  llerian ducts develop & mature as long as she’s not exposed to large amounts of testosterone </li></ul><ul><li>M  llerian Ducts </li></ul><ul><li>Precursor of female reproductive organs that develop into the oviduct, uterus & upper vagina during prenatal development </li></ul>
  7. 7. Organizing Effects of Sex Hormones <ul><li>The Sexually Dimorphic Nucleus </li></ul><ul><li>Part of the medial preoptic hypothalamus that is larger in males than in females </li></ul><ul><li>This area is linked to male sexual behavior </li></ul><ul><li>The female hypothalamus differs from the male hypothalamus </li></ul><ul><li>It can generate a cyclic pattern of hormone release; the male cannot </li></ul><ul><li>Sensitive Period </li></ul><ul><li>In early prenatal development, when a particular event has a long-lasting effect </li></ul><ul><li>A mammal with low levels of hormones in early development will develop female anatomy </li></ul><ul><li>Male characteristics develop with the introduction of testosterone </li></ul><ul><li>Alpha-fetoprotein </li></ul><ul><li>A protein that binds with estrogen & keeps it from entering cells during the early sensitive period </li></ul><ul><li>This process keeps females from becoming masculinized with their own estsrogen </li></ul><ul><li>Sex Differences in Nonreproductive Characteristics </li></ul><ul><li>If female fetuses are exposed to androgens, they tend toward masculine behaviors </li></ul><ul><li>Male & female brains differ in regions unrelated to sexual behavior </li></ul><ul><li>I.e. language areas of the left temporal lobe & the corpus callosum </li></ul>
  8. 8. Activating Effects of Sex Hormones <ul><li>Rat Research </li></ul><ul><li>Sex hormones activate sexual behavior partly by enhancing sensations </li></ul><ul><li>Medial preoptic area, ventromedial nucleus & anterior hypothalamus are principle areas affected by sex hormones </li></ul><ul><li>Sex hormones prime the MPOA & other areas to release dopamine </li></ul><ul><li>At low concentrations, dopamine stimulates D 1 and D 5 receptors which facilitate erections in male & sexually receptive postures in female rats </li></ul><ul><li>Higher concentrations of dopamine stimulate D 2 receptors which lead to orgasm </li></ul>
  9. 9. Sexual Behavior in Humans <ul><li>Effects on Men </li></ul><ul><li>Sexual excitement is highest when testosterone levels are highest </li></ul><ul><li>Sexual pleasure during orgasm is due to the secretion of large amounts of oxytocin </li></ul><ul><li>Decreases in testosterone levels generally decrease sexual activity </li></ul><ul><li>Impotence: the inability to have or maintain an erection </li></ul><ul><li>Usually not caused by low testosterone levels </li></ul><ul><li>Treated by increasing blood circulation in the penis & hypothalamus </li></ul><ul><li>Decreasing testosterone activity is a method to treat sex offenders </li></ul>
  10. 10. Sexual Behavior in Humans <ul><li>Effects on Women </li></ul><ul><li>Menstrual cycle: periodic variation in hormones & fertility over the course of about one month </li></ul><ul><li>At the end of the period, the anterior pituitary releases Follicle-stimulating Hormone (FSH) that promotes the growth of a follicle in the ovary </li></ul><ul><li>Toward the middle of the cycle the follicle produces increasing amounts of estradiol leading to an increase in release of FSH & LH from the anterior pituitary </li></ul><ul><li>At the end of the cycle, levels of LH, FSH, esstradiol & progesterone all decline </li></ul>
  11. 11. Sexual Behavior in Humans <ul><li>Effects on Women </li></ul><ul><li>Birth control pills containing estrogen & progesterone prevent a surge of FSH & LH that would release an ovum </li></ul><ul><li>This makes it harder for the sperm to reach the egg & for the egg to be implanted </li></ul><ul><li>Preovulatory period : the midpoint of the menstrual cycle when sexual interest increases </li></ul><ul><li>Premenstrual syndrome (premenstrual dysmorphic syndrome): characterized by anxiety, irritability & depression during the days before the menstruation </li></ul>
  12. 12. Sexual Behavior in Humans <ul><li>Nonsexual Behavior </li></ul><ul><li>Testosterone increases aggressive behavior in many species </li></ul><ul><li>Estrogen stimulates growth of dendritic spines in the hippocampus & prevents neuronal death </li></ul><ul><li>Estrogen increases the production of dopamine (D 2 ) & serotonin 5-HT 2A ) receptors in the nucleus accumbens, prefrontal cortex & several other cortical areas </li></ul><ul><li>Estrogen is linked to the ability to perform motor & cognitive skills </li></ul>
  13. 13. Parental Behavior <ul><li>The Biochemistry of Parenthood </li></ul><ul><li>Increase in oxytocin & prolactin by the day of delivery is necessary for maternal behavior in rats </li></ul><ul><li>Damage to the medial preoptic area impairs parental behavior in rats </li></ul><ul><li>Later stages of maternal behavior is not dependent on hormones </li></ul><ul><li>In male rats, testosterone levels drop after the delivery of the pups & prolactin levels increase </li></ul>
  14. 14. Interpertations of Mating Behavior <ul><li>Interest in Multiple Mates </li></ul><ul><li>Men are more likely to be interested in short-term sexual relationships with many partners </li></ul><ul><li>Men’s mating strategies: </li></ul><ul><li>One-mate strategy </li></ul><ul><li>Multiple-mate strategy </li></ul><ul><li>Evolutionarily, either strategy (or both) will be effective in spreading the man’s genes </li></ul><ul><li>Women have less to gain in multiple-mate strategy </li></ul><ul><li>They have a limited number of pregnancies </li></ul>
  15. 15. What Men & Women Prefer in a Mate <ul><li>Main Preferences </li></ul><ul><li>Healthy, intelligent, honest & physical attractiveness </li></ul><ul><li>Women’s Additional Preferences </li></ul><ul><li>Acceptable odor, being a good provider </li></ul><ul><li>Power is highly attractive </li></ul><ul><li>Men’s Additional Preferences </li></ul><ul><li>Physical appearance is important </li></ul><ul><li>Men have a strong preference for a younger partner </li></ul>
  16. 16. Jealousy <ul><li>Differences in Jealousy </li></ul><ul><li>Men tend to be more upset about wives’ sexual infidelities than women about their husbands’ infidelities </li></ul><ul><li>Women tend to be more upset about emotional infidelity than sexual infidelity </li></ul><ul><li>If a behavior has a clear advantage for survival or reproduction & is similar across cultures, it can’t be concluded it developed by evolution </li></ul>
  17. 17. Determinants of Gender Identity <ul><li>Gender Identity </li></ul><ul><li>How you identify yourself sexually & whether you call yourself male or female </li></ul><ul><li>Your sense of maleness or femaleness </li></ul><ul><li>Intersexes </li></ul><ul><li>If a female fetus is exposed to elevated androgen levels, than partial masculinization of her anatomy will occur </li></ul><ul><li>Hermaphrodites : individual whose genitals do not match normal development for their genetic sex </li></ul><ul><li>Intersexes (pseudohermaphrodite) : individuals whose development is intermediate between male & female (not androgynous) </li></ul>
  18. 18. Determinants of Gender Identity <ul><li>Androgen Insensitivity </li></ul><ul><li>Males with genital appearance of females </li></ul><ul><li>Cause: inability of androgens to bind to cells </li></ul><ul><li>Cells are insensitive to androgens & the external genitals develop similar to those of a female </li></ul><ul><li>5  -Reductase Deficiency </li></ul><ul><li>Genetic disorder in males where the penis does not develop until puberty & the child is usually identified as female </li></ul>
  19. 19. Biological Basis of Sexual Orientation <ul><li>Probability of Homosexuality </li></ul><ul><li>Highest in monozygotic twins of the originally identified homosexual person </li></ul><ul><li>Lowest in dizygotic twins </li></ul><ul><li>Lowest in adopted brothers & sisters </li></ul><ul><li>Genetic factors not only the determinant of sexual orientation </li></ul><ul><li>Animal Studies </li></ul><ul><li>Suggest low testosterone levels during pregnancy may cause male offspring to respond sexually to either male or female partner </li></ul><ul><li>Prenatal Stress </li></ul><ul><li>Prenatal stress decreases male sexual behaviors </li></ul><ul><li>Diethylstilbestrol (DES) , a synthetic estrogen can exert a masculinizing effect similar to testosterone </li></ul><ul><li>Brain Anatomy </li></ul><ul><li>Anterior commisure & suprachiasmatic nucleus is larger in homosexual men than in heterosexual men </li></ul><ul><li>Interstitial nucleus 3 of the anterior hypothalamus (INAH-3) in homosexual males & heterosexual females is similar in size, but smaller in heterosexual males </li></ul>