Chapter 8: Reproduction

Question 1

Female reproductive strategies

• ova
• investment
• mating

Answer 1

Limits to number of ova and offspring
Limits to age of fertility
Heavy investment in pregnancy and nurturance (choosy with males –want males w best traits so offspring have best survival chance)
Generally more cautious, as mating in wrong conditions can be costly (food storage, extremely hot/cold climate, lack of shelter)
Want to select optimal mate, but not always able

Question 2

Male reproductive strategies

• sperm
• investment
• mating

Answer 2

Sperm are numerous
Less required investment (in production and in caregiving)
Effort may end at insemination
Multiple matings propagate genes (mate with as many mate as possible, not choosy)
Intense competition with other males

Question 3

Males Issues

Answer 3

Paternity confidence (risk of cuckoldry)
Bonding usually requires confidence
Intermale competition (fighting for access for females, stronger=better genes)
Infanticide (males will kill offspring that are not his own)

Question 4

r

Answer 4

growth rate of population

Question 5

K

Answer 5

carrying capacity of environment (probability of survival)

Question 6

R-selected species (high r, low K)

Answer 6

•	Large number of offspring
•	Little investment
•	Short juvenile period
•	Low offspring survivability 
EX: sea turtle, fruit flies, fish, insects

Question 7

K-selected species (low r, high K)

Answer 7

•	Small number of offspring
•	Heavy investment (mostly from the mother)
•	Prolonged juvenile period
•	Higher offspring survivability
EX: larger mammals, humans

Question 8

Monogamy

Answer 8

one male and one female, lifelong

More dominant males lose reproductive potential
Lower status males gain reproductive potential
More dispersion of reproduction across all types of males
Female-female competition for dominant males

Question 9

Serial Monogamy

Answer 9

repeated 1 male and 1 female partnerships, limited duration

More dominant males lose reproductive potential
Lower status males gain reproductive potential
Female-female competition for dominant males

Question 10

Polygamy

Answer 10

Multiple pairings by both males and females

Question 11

Polygyny

Answer 11

Multiple pairings by one male and several females

Dominant males gain
Lower status males excluded
Intermale competition intensified
Lower status females access successful males
Competition among co-females

Question 12

Polyandry

Answer 12

Multiple pairings by one female and several males

Rare –Males often tied by kinship
Lower status females lose reproductive potential
Reduced infanticide
EX: bees (queen bee), humpback whales

Question 13

Promiscuity

Answer 13

no exclusive partnerships

Female choice
Disease risk high
Paternity uncertainty, thus males often do not bond/care for young care

Question 14

Polyamory

Answer 14

more than 1 partner in a relationship

Unique to humans (everyone in the group is consenting) –trust, emotional bond b/w individuals
Considered either a relationship practice OR sexual orientation

Question 15

Male-Female Bonding

Advantages

Answer 15

Decreased disease risk
Bi-parental care more effective
Higher quality offspring
Female gets assistance, provisioning, defense

Question 16

Male-Female Bonding

Disadvantages

Answer 16

Exclusion of other opportunities
Partner may not be fertile
Possibility of deception by partner
Male: sexual infidelity by female (cuckoldry)
Female: male may abandon / neglect / abuse

Question 17

Male Sexual Behaviour

mounting, intromission, ejaculation

Answer 17

Mounting: positioning on the female to permit copulation
Intromission: insertion of the penis with pelvic thrusting
Ejaculation: reflexive emission of sperm

Question 18

Male Basic Spinal Reflexes

Answer 18

Erection – parasympathetic NS
Ejaculation – sympathetic NS

L1, L2 (SNS) and S2/3/4 (PNS)
Damage to spinal cord above lumbar –both erection & ejaculation can still occur
Damage to spinal cord above sacral –erection can occur, ejaculation cannot

Question 19

Male Sex Hormone Synthesis

Answer 19

Hypothalamus–>GnRH–>Pituitary Gland–>LH (Leydig cells in testes–>testosterone) & FSH (Sertoli cells in testes–>inhibin)

Question 20

Hormones and Male Sexual Response

• testosterone levels
• experiment w Rhesus monkeys
• arousal

Answer 20

Testosterone levels highest in the morning, decrease throughout the day (similar to cortisol)
Levels vary among males (at any given time during the day)

Castration reduces male sexual response, but not always (adrenals and experience)
Experiment:
- Intact (still had testes): 75% of time ejaculation occurs
- Castrated: 15-20% of cases had ejaculation initially, increased to 50-55% when injected with dihydrotestosterone (more successful mating)
o Maintained testosterone levels =better reproduction success

Male arousal facilitated by minor increases in general arousal and catecholamines
Male arousal dampened by major stress, fatigue, and over-arousal

Question 21

Shafik (1996)

Underwear experiment

Answer 21

Materials containing polyester caused erectile disfunction in the 12 months of wearing the pants, recovers after removing pants
Greater electrostatic potentials in the polyester-containing groups –higher friction b/w underpants and genitals =erectile disfunction

Question 22

Female Sexual Behaviour

reflexes, proceptivity, receptivity

Answer 22

Reflexes: spinal (e.g. lubrication, blood flow, lordosis)
Proceptivity: extent which a female will elicit copulations as reflected by her behaviour
- Anal-genital sniffing, push themselves underneath the male, bit at their neck

Receptivity: female’s state of responsiveness to sexual initiation by male
• Female sexual reflexes generally inhibited by stress & stress hormones
• Facilitated by parasympathetic NS

Question 23

Female Basic Spinal Reflexes

Answer 23

Lubrication, blood flow, lordosis (arched back)
Female sexual reflexes generally inhibited by stress and stress hormones
Facilitated by PNS

Question 24

Female Sex Hormone Synthesis

Answer 24

Hypothalamus–>GnRH–>Pituitary Gland–>LH (->estrogen) & FSH (–>inhibin)

Question 25

FSH

Answer 25

causes release of inhibin acting on pituitary gland in males/females
Stimulates gamete production in males/females
Males –stimulates spermatogenesis (production of sperm)
Females –stimulate follicle growth in ovaries

Question 26

Birth Control Pills

• estrogen levels
• estrogens
• progestins

Answer 26

Increase estrogen levels –causes increase in negative feedback loop (no/little production of LH)

Estrogens: inhibit FSH & LH secretion from pituitary
- Prevention of ovulation b/c no LH surge occurs

Progestins: inhibit LH secretion from pituitary

• Increased cervical mucus
• Make uterine lining inhospitable for fertilized egg

Question 27

Early Sexual Differentiation

• masculinization
• feminization

-SRY gene

Answer 27

Occurs during first trimester (6-7 weeks gestation)

Masculinization: Mullerian ducts degrade, Wolffian ducts become epididymis and ductus deferens (testes)
Feminization: Wolffian ducts degrade, Mullerian ducts become uterine tubes and uterus (ovaries, urinary bladder, urethra, uterus, vagina)

• SRY gene on short arm of Y-chromosome is expressed in the primordial gonads, leading to TDF release
• Embryonic testes release Testosterone to stimulate Wolffian duct growth (male system) and Mullerian Inhibitory Hormone (MIH) to suppress Mullerian duct growth (female system)
• Dihydrotestosterone (DHT): fusion of external genitalia

Question 28

SDN-POA of the hypothalamus

Answer 28

Perinatal—in rodents—(or prenatal in humans) testosterone surge critical for masculine development (comes from testes of fetus)
Without this testosterone surge, the brain is feminine for life
SDN-POA larger in males

Question 29

Intrauterine position of mice influence behaviour

Answer 29

2M Females show less lordosis behaviour, more aggression, less matings from males (less attractiveness to males), less mounts by males
2F males have smaller SDN-POA and decreased testosterone
- 2M means pup was surrounded by 2 male pups in uterine horn
- Males surrounded by more females=higher levels of estrogen, less testosterone
- Females surrounded by less males= higher levels of estrogen, less testosterone

Question 30

Preoptic area (POA)

Answer 30

critical for male sexual behaviour

Question 31

Ventromedial hypothalamus (VMH)

Answer 31

critical for female sexual behaviour

Question 32

Male Brains

• lesion to POA
• damage to amygdala

Answer 32

Lesioning the POA ends male sexual response for life
Electrical stimulation of the POA –sexual excitement and mating behaviour

Damage to the amygdala and areas in the temporal lobes =hypersexuality in cats (experimental) and humans (observational)

Question 33

Female Brains

• lesion to VMH
• septum

Answer 33

Lesioning of VMH reduces female sexual receptivity
Estrogen applied to VMH produces sexual receptivity

POA may inhibit female sexual behaviour

Lesioning the septum =increased sexual receptivity
Stimulating the septum =decreased sexual receptivity

Question 34

Female Fertility

Answer 34

Longer duration of mating is associated with more successful fertilization
Female arousal diminishes barriers to sperm (i.e. cervical opening, lubrication)
Oxytocin is released during orgasm and can produce uterine contractions

Question 35

Medial Preoptic Area (MPOA) of hypothalamus

Answer 35

critical in maternal care

Blood transfusion to virgin can induce maternal care

Question 36

Prolactin vs Oxytocin

Answer 36

stimulates milk production

causes milk release
Crying infant can cause milk release

Question 37

Homosexuality

Answer 37

No hormonal difference (no difference in androgen, i.e. testosterone) between homosexuals and heterosexuals males

INAH3 smaller in homosexual males (also smaller in females than males)

Higher rate of homosexuality with increasing number of older brothers

Question 38

Bailey & Pillard (1991)

Male homosexuals with MZ twins, DZ twins, or adoptive brothers

Answer 38

Likelihood of being homosexual: MZ>DZ>adoptive siblings

Question 39

Hamer et al. (1993)

Homosexuality & Lineage

Answer 39

Higher concordance of homosexuality in males from maternal linage