Hormones: sex determination and sex differences

Question 1

Physiological and behvaioral sex differences

Answer 1

1) Early develeopemental control (organisational)
2) later Behavioral control (activational) -> e.g. breeding season

• agression
• copulation
• courtship
• parental behaviors

Ensures that organisms are both sexually mature and present in a suitable environment (e.g. enough mates and nests) before they can reproduce

Example:
- Male Zebra finche testoerone release during puberty ensures they are sexually mature
- When there is a suitable presence of Mates and nests the release of androgens from the testes increases -> allows singing

Question 2

Sex hormones

Answer 2

testes -> androgens (e.g. testosterone)

ovaries -> estorgen and progesterone

Testosterone can be feminizing or masculinising
- Reductase -> androgens (masculinising)
- Aromaase -> estriol (feminising)

Don’t necesary for all male sexual behaviors
e.g. white-crowned sparrows, sexual behaviour is maintained post testes removal

Question 3

Early developementl control (organisational)

Answer 3

Sex and early develeopement determined by an interaction between genetics and hormones

1) Males (XY) and females (XX) chromosomes encode genes determining fate of gonads
2) SRY and SOX9 expressesion from Y chromosome leads to testes (ovary formation if not present-> female is default)
3) Gonad release hormones controlling developement

Birds
- Male (ZZ) and female (ZW)
- male is default

Examples showing hormonal control:
- Hormone exposure during critical developement periods effect develeopement and later expression of behavior

Birds
- If aromatase inhibitor are injected into female eggs inhbiting estrogen formation -> masculinised females performed male sexual behaviors
- If Estrogen is injected in male eggs -> demasculinised males with ovary develeopement

Rhesus monkeys
- Females exposed to androgens have masculinised genitals and engage in more rough play as juvenilles

Example showing genetic control: Zebra finch gynandromorphs
- one gametically female side, and the other is gametically male due to one ovary and one tested
- Hormones circulate whole body yet sex differences appear on different sides of the body.

Non chromosomal sex determination: temperature
- Sex determined by temp in many fish + reptiles as temp activates aromatase and/or reductase leading to masculising/ feminising hormomes
eg. turtles = warm temp (egg buried less deep) → more females

Can also get sequential hermaphrodites (e.g. parrotfish) and different male morphotypes (e.g. Midshipman)

Question 4

organisational control allowing activational control

Answer 4

The morphological changes during develeopement lead to behavioral sex differences later in life

Brain
- Sex hormones feminise/masculinise the developing hypothalamus and other areas of the developing brain. (e.g. size of regions) -> primes body to respond to hormones later in life
- This establishes the foundations for the performance of masculine or feminine behaviours by adults

Example: Zebra finshes
- The HVS and the RA of the brain are 6x larger in males than females, and area X can only be found in females
- Large HVS allows male song production once they are sexually mature
- Able to induce song in females by giving estradiol early in life and testosterone later.
- Not able to unduce singing by just gicing females testosterone later in life -> need organisational to get activational

Requires puberty
- Surge in utero or soon after birth leading to sexual differentiation
- decrease in childhood (trade off with immune system)
- Second surge suring puberty leading to secondary sexual traits and levels remain high.

Question 5

Later behavioral control (Activational)

Answer 5

Sex hormones target aspects of this system to elicit certain response in the appropriate behavioural or social context.

Example: increased testosterone in male birds during breeding season
- increased aggression, increased muscle mass, territoriality, courtship behaviour and copulatory behaviours
- e.g. Manakins adult males testosterone increased in breeding season -> develop a brilliant and conspicuous plumage, establish an arena, and display to females involving rapid jumps, short dances, brief flights, and the erection of feather tracts
- e.g. Study showed increased binding of radioactive testosterone in cells of the spinal cord, containing motoneurons, which control the wings and leg muscles used in the sexual displays during breeding season
- e.g. testosterone necessary for parental care in male California mice -> castration = less paternal

Example: increased oestrogen and pregestins in the breeding season
- female receptive behaviours (more likely to allow copulation) and parental care

But-> testoesterone release does not immediately effect sexual behavior
- Study found that if castration occured before hiberndation it effected sexual behavior but if occured right before breeding it did not

Question 6

Behavior -> hormone feedback

Answer 6

Allows behaviours to be closely regulated under changing conditions

Example: Birds

Hormone -> behavior
Exposure to a potential mate leads to an increase in male testosterone levels within 4 hours, and these levels remain high throughout courtship -> promotes spermatogenesis

Behavior -> hormone
Successful mating leads to progesterone release -> promotes brooding and nest-building behaviours

Example: Cichlid fish

Behavior -> hormone
- When males have territorial conflicts, defeated males have a drop in endogenous testosterone making them less likely to win another fight and winners have a spike
- If dominant males are removed, subordinate males will regain testosterone and become more aggressive

Context also impacts hormone release

Example: Squirrel monkey
- alpha-males have higher endogenous testosterone when females live in groups
- testosterone levels also correlate with rank status

Question 7

How to study hormonal effects on behavior

Answer 7

Detect causal link between hormone + behaviour using …
1) Blockade – behaviour should disappear if remove hormone
2) Reinstatement – behaviour returns if restore hormone
3) Concentration dependence – hormone conc affects behaviour (more behave if higher conc)

This can be done via …
1) Ablation – removing hormone-producing gland or knocking out gene for hormone receptor
2) Bioassay – injecting different does of hormone into live subject

Question 8

Menstral cycle

Answer 8

Varying hormone levels during eostrogen cycle effect female sexual activity

Around Ovulation -> high estrogen so more receptive
e.g. female rhesus monkeys will actively seek male companionship when in oestrus (also effected by social environment-> multiple females then male only pairs up during oestrus)

Post ovulation -> high progesterone to prepare uteral endometrium for embryo implantation (more progeseteron = higher fecundity)
e.g. higher ranking goats produce more progesterone

Synchronising estrogen cycles in lions
- shared rearing / care / suckling
- male cubs born at same time as other male cubs have better chance of winning pride as go as pair