Chapter 10 - Chapter 10 Chapter Reproductive behavior...

Unformatted text preview: Chapter 10 Chapter Reproductive behavior Reproductive behaviors Reproductive Constitute the most important category of social behaviors, because Constitute without them, most species would not survive without These behaviors (e.g. courting, mating, parental behavior) are These categories of sexually dimorphic behaviors, ii.e. behaviors that differ .e. sexually in males and females in Hormones present both before and after birth play a role in the Hormones development and control of sexually dimorphic behaviors development Sexual development Sexual Production of gametes and Production fertilization fertilization The production of gametes (ova and The gametes sperm) is a special form of cell division: produces cells that contain one member of each of the 23 pairs of chromosomes; the development of a human begins at the time of fertilization, when a sperm and ovum join, sharing their chromosomes to create 23 pairs chromosomes The last pair of chromosomes The determines the sex of the offspring (sex chromosomes; XX female, XY male) chromosomes Sexual development Sexual Development of the sex organs Only sex hormones are responsible for our sexual dimorphism 3 general categories of sex organs: • Gonads – testes or ovaries produce ova or sperm and secrete hormones produce the factor that controls their development into either testes or ovaries is the a single gene on the Y chromosome called Sry, which produces a Sry which protein called testis-determining factor; thus if not present, ovaries testis-determining thus develop develop Sexual development Sexual Development of the sex organs (con’t) Gonads (con’t) Internal sex organs • Müllerian system – the embryonic precursors of the female internal sex organs organs • Wolffian system – the embryonic precursors of the male internal sex organs • Gender of fetus determined by presence or absence of hormones secreted Gender by the testes: by Anti-Müllerian hormone prevents female system from developing (defeminizing effect) effect Androgens – stimulates development of Wolffian system (masculinizing effect) • Once gonads have developed, a series of events directed by hormones Once occur that determine the gender of the offspring occur • Two effects: Organizational effects – the effect of a hormone on tissue differentiation and development; occurs during prenatal development development; Activational effects – the effect of a hormone that occurs in the fully developed organism; may depend on the organism’s prior exposure to the organizational effects of hormones effects Sexual development Sexual Development of the sex organs (con’t) Internal sex organs (con’t) • Two types of androgens Testosterone – secreted from testes; principle androgen found in males Dihydrotestosterone – an androgen, produced from testosterone through the action of the enzyme 5α reductase action • The Wolffian system thus contains androgen receptors in order for the The androgens to take action androgens • Androgen insensitivity syndrome – a condition caused by a congenital lack of functioning androgen receptors; in a person with XY sex chromosomes, causes the development of a female with testes but no internal sex organs causes • Persistent Müllerian duct syndrome – condition caused by a congenital lck of anti-Müllerian hormone or receptors for this hormone; in a male, causes development of both male and female internal sex organs development • Tuner’s syndrome – the presence of only one sex chromosome (X); characterized by lack of ovaries but otherwise normal female sex organs and genitalia genitalia Androgen Insensitivity Syndrome Syndrome Sexual development Sexual Development of the sex organs (con’t) External genitalia • Visible sex organs, including penis and scrotum in males and labia, clitoris, and the Visible outer part of the vagina in females outer • In the presence of dihyrdotestosterone the external genitalia will become male Sexual maturation Primary sex characteristics include gonads, internal sex organs, and external Primary genitalia; all present at birth genitalia; Secondary sex characteristics (e.g. enlarged hips and breasts, facial hair and Secondary deep voice) appear at puberty deep The onset of puberty occurs when the cells in the hypothalamus secrete The gonadotropin-releasing hormone (GnRH), which stimulates the production of 2 gonadotropin-releasing gonadotropic hormones by the anterior pituitary gland gonadotropic • Follicle-stimulating hormone (FSH) – causes development of an ovarian follicle and the maturation of an ovum maturation • Luteinizing hormone – causes ovulation and development of the ovarian follicle into a corpus luteum corpus • Both hormones are also produced in males, to stimulate the testes to produce sperm Both and to secrete testosterone and Sexual development Sexual Sexual maturation (con’t) In response to the gonadotropins, the gonads secrete steroid sex In hormones hormones • e.g. the ovaries produce estradiol one of a class of hormones known as e.g. estradiol estrogens estrogens Hormonal control of sexual behavior behavior Female reproductive cycles Menstrual cycle – primate species; characterized by the growth of the lining of the uterus, ovulation, development of a corpus luteum, and (if pregnancy does not occur), menstruation pregnancy Other species have estrous cycles Other estrous Cycle begins with secretion of gonadotropins by the anterior pituitary, Cycle which stimulate the growth of ovarian follicles, and ovulation (release of ovarian and ovum); the ruptured ovarian follicle becomes a corpus luteum and corpus produces estrodiol and progesterone (promotes pregnancy) estrodiol progesterone Hormonal control of sexual behavior behavior Sexual behavior of lab animals Males • Male sexual behavior is quite varied, however, the essential features Male (intromission, pelvic thrusting, and ejaculation) are characteristic of all male mammals mammals • Rat sexual behaviors studied most • After ejaculation, males enter a refractory period, during which they cannot After refractory during ejaculate again ejaculate • In behavioral studies, observe Coolidge effect – the restorative effect of In Coolidge introducing a new female sex partner to a male that has apparently become “exhausted” by sexual activity “exhausted” Females • Lordosis – a spinal sexual reflex seen in many four-legged female mammals; arching of the back in response to approach of a male or to touching the flanks, which elevates the hindquarters flanks, Hormonal control of sexual behavior behavior Masculinization and Defeminization If a rodent brain is exposed to androgens during development, two If phenomenon occur: phenomenon • Behavioral defeminization – the organizational effect of androgens that Behavioral prevents an animal from displaying female sexual behaviors in adulthood prevents • Behavioral masculinization – enables animals to engage in male sexual Behavioral behavior behavior Effects of pheromones A chemical released by one animal that affects the behavior or chemical physiology of another animal; usually smelled or tasted physiology Whitten effect – the synchronization of the menstrual or estrous cycles of a group of females, which occurs only in the presence of a pheromone in a male’s urine pheromone Detection of pheromones is mediated by the vomeronasal organ (VNO), Detection vomeronasal which projects to the olfactory accessory bulb which Olfactory accessory bulb then projects to the medial nucleus of the Olfactory amygdala, which then projects to the hypothalamus amygdala Hormonal control of sexual behavior behavior Human sexual behavior Activational effects of sex hormones in women • In higher primates (including humans), ovarian hormones are not necessary In to have intercourse, as with other mammals to • However, ovarian hormones can have an influence on their sexual interest In men • Levels of testosterone not only affect sexual activity, but is also affected by it Sexual orientation Sexual Exclusive homosexuality appears to occur only in humans A llikely biological cause of homosexuality is a subtle difference in ikely brain structure cased by differences in the amount of prenatal exposure to androgens exposure However, these are speculations and have not been supported by However, speculations human data human Congenital adrenal hyperplasia – a condition characterized by hypersecretion of androgens by the adrenal cortex; in females, causes masculinization of the external genitalia; studies have seen a higher proportion of homosexual women with this disorder higher The sexual dimorphism of the brain (e.g. different sizes, more The sharing of functions in female brains) may be a result of differential exposure to androgens during early postnatal life exposure Many studies have shown possible relations between sizes of Many certain brain structures and homosexuality; however, no real conclusive data conclusive Neural control of sexual behavior Neural Males Spinal mechanisms • Some sexual response are controlled by neural circuits in the spinal Some cord (e.g. erection and ejaculation) cord • e.g. spinal nucleus of the bulbocavernosus in the male rat e.g. spinal Brain mechanisms • Both excitatory and inhibitory controls over the spinal mechanisms • e.g. medial preoptic area – most critical for sexual behavior in males e.g. medial • Sexually dimorphic nucleus – larger in males than in females; plays a role in male sexual behavior role • Periaqueductal gray matter – region of the midbrain that surrounds the cerebral aqueduct; plays an essential role in various species typical behaviors typical Neural control of sexual behavior Neural Females Ventromedial nucleus of Ventromedial the hypothalamus – plays the an essential role in female sexual behaviors; injection of ovarian hormones into the nucleus will elicit sexual behavior even in females without ovaries females Parental behavior Parental Maternal behavior of rodents Hormonal control of maternal behavior During gestation (pregnancy) female rats and mice build nests At the time of parturition (giving birth), the female will prepare herself for labor, At parturition and afterwards nurse the pups and Mother will lick the pups’ anogenital region in order to stimulate urination and Mother defecation defecation Will retrieve pups that may leave the nest Continue to nurse the pups until weaning No evidence that organizational effects of hormones play a role Although hormones may affect maternal behavior, they do not control them Neural control of maternal and paternal behaviors The medial preoptic area plays a role in maternal behavior (lesions elicit The indifference towards pups in new mothers) indifference In some species, the male will care for the offspring (e.g in monogamous prairie In vols) vols) ...
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