1. Reproductive behavior
Chapter 10
Reproductive behavior

2. Reproductive behaviors
Constitute the most important category of social behaviors, because without them, most species would not survive
These behaviors (e.g. courting, mating, parental behavior) are categories of sexually dimorphic behaviors, i.e. behaviors that differ in males and females
Hormones present both before and after birth play a role in the development and control of sexually dimorphic behaviors

3. Sexual development Production of gametes and fertilization
The production of gametes (ova and 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
The last pair of chromosomes determines the sex of the offspring (sex chromosomes; XX female, XY male)

4. Sexual development 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
the factor that controls their development into either testes or ovaries is a single gene on the Y chromosome called Sry, which produces a protein called testis-determining factor; thus if not present, ovaries develop

5. Sexual development Development of the sex organs (con’t)
Gonads (con’t)
Internal sex organs
Müllerian system – the embryonic precursors of the female internal sex organs
Wolffian system – the embryonic precursors of the male internal sex organs
Gender of fetus determined by presence or absence of hormones secreted by the testes:
Anti-Müllerian hormone prevents female system from developing (defeminizing effect)
Androgens – stimulates development of Wolffian system (masculinizing effect)
Once gonads have developed, a series of events directed by hormones occur that determine the gender of the offspring
Two effects:
Organizational effects – the effect of a hormone on tissue differentiation and development; occurs during prenatal 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

7. Sexual development 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
The Wolffian system thus contains androgen receptors in order for the androgens to take action
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
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
Tuner’s syndrome – the presence of only one sex chromosome (X); characterized by lack of ovaries but otherwise normal female sex organs and genitalia
Congenital – present at birth; due to heredity

8. Androgen Insensitivity Syndrome

9. Sexual development Development of the sex organs (con’t)
External genitalia
Visible sex organs, including penis and scrotum in males and labia, clitoris, and the outer part of the vagina in females
In the presence of dihyrdotestosterone the external genitalia will become male
Sexual maturation
Primary sex characteristics include gonads, internal sex organs, and external genitalia; all present at birth
Secondary sex characteristics (e.g. enlarged hips and breasts, facial hair and deep voice) appear at puberty
The onset of puberty occurs when the cells in the hypothalamus secrete gonadotropin-releasing hormone (GnRH), which stimulates the production of 2 gonadotropic hormones by the anterior pituitary gland
Follicle-stimulating hormone (FSH) – causes development of an ovarian follicle and the maturation of an ovum
Luteinizing hormone – causes ovulation and development of the ovarian follicle into a corpus luteum
Both hormones are also produced in males, to stimulate the testes to produce sperm and to secrete testosterone

12. Sexual development Sexual maturation (con’t)
In response to the gonadotropins, the gonads secrete steroid sex hormones
e.g. the ovaries produce estradiol one of a class of hormones known as estrogens

13. Hormonal control of sexual 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
Other species have estrous cycles
Cycle begins with secretion of gonadotropins by the anterior pituitary, which stimulate the growth of ovarian follicles, and ovulation (release of ovum); the ruptured ovarian follicle becomes a corpus luteum and produces estrodiol and progesterone (promotes pregnancy)

15. Hormonal control of sexual behavior
Sexual behavior of lab animals
Males
Male sexual behavior is quite varied, however, the essential features (intromission, pelvic thrusting, and ejaculation) are characteristic of all male mammals
Rat sexual behaviors studied most
After ejaculation, males enter a refractory period, during which they cannot ejaculate again
In behavioral studies, observe Coolidge effect – the restorative effect of introducing a new female sex partner to a male that has apparently become “exhausted” by sexual activity
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

17. Hormonal control of sexual behavior
Masculinization and Defeminization
If a rodent brain is exposed to androgens during development, two phenomenon occur:
Behavioral defeminization – the organizational effect of androgens that prevents an animal from displaying female sexual behaviors in adulthood
Behavioral masculinization – enables animals to engage in male sexual behavior
Effects of pheromones
A chemical released by one animal that affects the behavior or physiology of another animal; usually smelled or tasted
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
Detection of pheromones is mediated by the vomeronasal organ (VNO), which projects to the olfactory accessory bulb
Olfactory accessory bulb then projects to the medial nucleus of the amygdala, which then projects to the hypothalamus

19. Hormonal control of sexual behavior
Human sexual behavior
Activational effects of sex hormones in women
In higher primates (including humans), ovarian hormones are not necessary to have intercourse, as with other mammals
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

20. Sexual orientation
Exclusive homosexuality appears to occur only in humans
A likely biological cause of homosexuality is a subtle difference in brain structure cased by differences in the amount of prenatal exposure to androgens
However, these are speculations and have not been supported by human data
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
The sexual dimorphism of the brain (e.g. different sizes, more sharing of functions in female brains) may be a result of differential exposure to androgens during early postnatal life
Many studies have shown possible relations between sizes of certain brain structures and homosexuality; however, no real conclusive data

21. Neural control of sexual behavior
Males
Spinal mechanisms
Some sexual response are controlled by neural circuits in the spinal cord (e.g. erection and ejaculation)
e.g. spinal nucleus of the bulbocavernosus in the male rat
Brain mechanisms
Both excitatory and inhibitory controls over the spinal mechanisms
e.g. medial preoptic area – most critical for sexual behavior in males
Sexually dimorphic nucleus – larger in males than in females; plays a role in male sexual behavior
Periaqueductal gray matter – region of the midbrain that surrounds the cerebral aqueduct; plays an essential role in various species typical behaviors

23. Neural control of sexual behavior
Females
Ventromedial nucleus of the hypothalamus – plays an essential role in female sexual behaviors; injection of ovarian hormones into the nucleus will elicit sexual behavior even in females without ovaries

24. Parental behavior Maternal behavior of rodents
During gestation (pregnancy) female rats and mice build nests
At the time of parturition (giving birth), the female will prepare herself for labor, and afterwards nurse the pups
Mother will lick the pups’ anogenital region in order to stimulate urination and defecation
Will retrieve pups that may leave the nest
Continue to nurse the pups until weaning
Hormonal control of maternal behavior
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 indifference towards pups in new mothers)
In some species, the male will care for the offspring (e.g in monogamous prairie vols)