BN Unit 2 Exam: organisational/activational, genes, environment

What is the female-typical mating posture in rodents?

Lordosis

What is the male-typical mating behavior in rodents?

Mounting

What happens to mounting after a male rodent is castrated, and after castration + testosterone?

Castration → no mounting; castration + testosterone → mounting returns

What makes rodent lordosis and mounting good models for hormone research?

They are sexually dimorphic behaviors under the control of gonadal steroid hormones

What two questions did William Young's studies ask?

What happens if females are given testosterone, and if castrated males are given estrogens and progestins?

What species did William Young study?

Guinea pigs

What treatment did Young give to pregnant guinea pigs?

Testosterone propionate (TP) injections across gestation: high dose, low dose, or none (controls)

What did the external genitalia of the high-dose females (HDF) look like?

Atypical — described as "hermaphrodites"

What did the external genitalia of the low-dose females (LDF) look like?

Typical — "unmodified females"

What three steps were used to test Young's animals as adults?

All gonadectomized as adults → injected with estrogen/progesterone and paired with a stud male → later injected with androgens and paired with a female in mating condition

In Young's study, how did HDF, LDF, and control females respond to estrogen/progesterone + a stud male?

HDF and LDF: decreased lordosis; CF: normal lordosis

What did the decreased lordosis in HDF and LDF show?

Androgens during development caused defeminization

In Young's study, how did HDF, LDF, and control females respond to androgens + a receptive female?

HDF and LDF: increased mounting; CF: normal (low) mounting

What did the increased mounting in HDF and LDF show?

Androgens during development caused masculinization

Why were Young's low-dose females especially important?

Their genitals looked normal, yet their behavior was defeminized and masculinized → hormones organize the brain separately from the genitals

What is the organizational effect of sex steroids?

During development, they organize/"program" the nervous system for later male- or female-typical behavior

When is the organizational period in humans vs rodents?

Humans: prenatal; rodents: perinatal

Are organizational effects temporary or permanent? Give examples of tissues.

Permanent changes (e.g., genitals, brain)

What is the activational effect of sex steroids?

In adulthood, the same hormones activate, modulate, or inhibit the functions of existing neural circuits

When do activational effects occur, and what can they modulate?

After early development; they can modulate cell growth or activity (including neural)

What happens when females are ovariectomized as adults and then given androgens?

Little/no mounting (no early organization by androgens)

What happens when females are given androgens before day 10 and again as adults?

They mount (organized early, activated in adulthood)

What happens when males are castrated at day 20 and given estrogen/progestin as adults?

No lordosis — the brain was already defeminized

What happens when males are castrated at day 1 and given estrogen/progestin as adults?

Lordosis — castrated before defeminization could occur

What is a gynandromorphic zebra finch?

A bird that is genetically ZW (female) on one half and ZZ (male) on the other half

Why is the gynandromorphic zebra finch a powerful natural experiment?

Both halves are exposed to the same hormonal conditions, so any differences must come from sex-chromosome-linked genes

What three things differed between the two halves of the gynandromorphic finch?

Plumage, gonads, and neural structures regulating song

Which brain hemisphere of the gynandromorphic finch showed the masculine song-system phenotype?

The right hemisphere

What gene expression pattern was seen in the gynandromorph brain?

The W-linked gene (ASW) was expressed only on the female (ZW) side; the Z-linked gene (PKCIZ) was higher on the male (ZZ) side

What did the gynandromorphic finch show about sexual differentiation?

Genetic sex of brain cells directly influences brain development, independent of hormones

In the intrauterine position effect, what does "2M" mean, and how does it compare to "0M"?

A fetus between two males; it gets more androgen exposure later in gestation than a 0M fetus (between no males)

What broad types of traits can intrauterine position affect?

Morphology, behavior, and physiological characteristics

How do 2M females differ in anogenital distance compared to 0M females?

Longer, more male-like anogenital distance (subtly masculinized genitals)

How do 2M females differ behaviorally from 0M females?

More interfemale aggression; less attractive to males

How do 2M females differ in reproductive physiology from 0M females?

Longer ovarian cycles, but no change to reproduction

What is a freemartin?

A masculinized, almost always infertile heifer born as twin to a bull

How does a freemartin come about?

In cows pregnant with twins, placental membranes fuse and blood is exchanged; a male twin's hormones masculinize the female

What percentage of freemartins are infertile?

Almost 100%

How is maternal stress during gestation studied in rodents?

Pregnant dams are stressed (e.g., restraint)

Which sex of offspring shows the strongest effects of prenatal maternal stress?

Males

How does prenatal maternal stress affect male offspring's hormones and mating?

They produce less androgen than control males and show reduced mating behavior

How does prenatal maternal stress affect male offspring's parenting and aggression?

Less infanticide, more parental care, reduced aggression

What brain changes occur in prenatally stressed males?

Changes in sexually dimorphic brain regions

How does prenatal stress affect rough-and-tumble play?

Reduced, especially in males (stressed males play less than control males)

What maternal behavior can influence sex-differentiated physiology and behavior after birth?

Licking and grooming, especially anogenital licking

Besides affecting sex differentiation, what does anogenital licking do for pups?

Stimulates elimination of waste

What adult behavior in males requires maternal anogenital licking?

Normal adult male mating behavior

Which pups get licked more, and what cues drive this?

Males > females; driven by testosterone and chemosensory cues from the pups

What are endocrine-disrupting chemicals (EDCs)?

Chemicals used in industry and personal products that mimic, block, or interfere with normal endocrine function

Name five classes of EDCs from the slide.

Bisphenols, phthalates, pesticides, parabens, PFAS

Which hormone systems are most commonly affected by EDCs?

Estrogen, androgen, and thyroid hormones

Name specific EDCs from the body-diagram slide.

BPA, octylphenol (OP), D4 (octamethylcyclotetrasiloxane), ioxynil (IOX), DES, PCBs

Which body systems did the EDC diagram show being affected?

Brain/nervous, cardiovascular, metabolic (obesity, insulin), reproductive (e.g., premature breast development, gynecomastia, disrupted cycles/fertility), and hormone-related cancers

What type of chemical is DDT?

A pesticide (an EDC)

What effect did DDT have on bird eggs?

Significant eggshell thinning

What reproductive changes did offspring of DDT-exposed birds show?

Right oviduct developed; males developed oviducts; right gonad became an ovotestis; reduced reproductive behavior in males

What three problems were seen in Florida panthers linked to EDCs?

Declining numbers, cryptorchidism, higher estrogen than androgen concentrations

Which animal groups show breeding disruptions due to environmental hormones?

Amphibians, reptiles, birds, and mammals

What three EDC-linked changes have been reported in humans?

Increased cryptorchidism, increased hypospadias, decreased sperm and semen production

What is cryptorchidism?

Undescended testes

What is hypospadias?

A urethral opening on the underside of the penis rather than the tip