Sexual determination and differentiation

behavioral dimorphism key points

bigger differences in behavior between same sex than opposite sex

environment matters

josts levels of sexuality

chromosomal

gonadal

gametic

hormonal

morphological

behavioral

major costs of sex

only have half the daughters that asexual organisms have

each offspring only carries half her genes

major costs of asexuality

accumulation of bad mutations

intrasexual selection

access to opposite sex or resources

intersexual selection

runaway

direct and indirect benefits

proximate causes of sex differences

1. steroid hormones

2. organizational: early hormone exposure organizes neural substrates subserving behaviors

3. activational: later hormone exposure that activates sexually differentiated neural substrates

where does mammalian gonad develop

from germinal ridge

where does mammalian ovary develop

from cortex of germinal ridge

where does mammalian testis develop

from inner medulla of germinal ridge

female path

mullerian ducts develop while wolffian ducts degenerate

male pathway

Wolffian ducts develop while Mullerian ducts degenerate

occurs from T and AMH

what does DHT do

organizes primordium to male typical anatomy

what does DHT production depend on

5a-reductase

turner syndrome

X O

female phenotype but sterile

Androgen insensitivity syndrome

lack androgen receptors

testicular feminization

congenital adrenal hyperplasia

overproduction of androgens by fetal gonads

lack of 21-hydroxylase enzyme overproduces androgens

avian sexual differentiation

females are heterogametic ZW

QUAIL sexual differentiation experiment

treating w/ E2 will feminize behavior while blocking E2 masculinizes behavior

if female bird given aromatase inhibitor she is masculinized

T and male lizards

Highest T males are orange-blue and more territorial

Lowest T males are solid orange and nonterritorial

aggression and aromatase

aromatase and aggression in sex changing fish inversely correlated

aromatase in sex changing fish

aromatase RNA elevated in ovaries then declines at onset of sex change

DMRT1

low in ovaries, increases at onset of sex change

prenatal hormones and sex differentiation

females masculinized by exposure to androgens from male twin

externally female, but variable duct development and testes-like gonads

F next to more brothers have higher T

Sex differences in OAEs

females have more and stronger OAEs than males

prenatal androgens and hyenas

F masculinized by prenatal T have more stillborn pups

organizational/activational experiment part 1

high T given to pregnant guinea pigs caused hermaphroditism

low T not different than control females external

control: untreated pregnant guinea pigs

organizational/activational experiment part 2

tested as adults

androgen treated females showed disruption of lordosis behavior and enhanced mounting behavior

no effects on males

similar effects in rats

conclusions of organizational/activational experiment

distinction between prenatal and postnatal actions of hormones

prenatal and perinatal periods for organizational effects

organization of neural tissues similar to gonadal accessory structures

effects can be subtle: behavior changes without changing genitals

who performed organizational and activational experiment

William Young

Nelson and Kriegsfeld summary

gonadal steroids have organizing effects on behavior

organizational effects restricted to particular time during development

asymmetry exists in relative effects of testes and ovaries

RODENT brain and T and E

masculinized neonatally by estrogen

preventing aromatization of T or blocking ER prevents masculinization

how are female rats androgenized

T administered then converted to E2 and binds to estrogen receptors to masculinize the brain

what happens when aromatase blocked in rodents neonatally

prevents masculinization

antisense approach

reverse complement oligonucleotide to mRNA of interest to block ER

1st structural dimorphism

preoptic area of rat

synapses on dendrite spines: F>M

synapses on dendrite shafts: F<M

Sexually dimorphic nucleus of preoptic area (SDN-POA)

Males>females, neonatally castrated males

TFM mice: female genitalia, male SDN-POA

Grows from T during perinatal sensitive periods

TFM mice structure

(lack androgen receptors) female genitalia but male SDN-POA

rat posterodorsal medial amygdala (MePD)

responds to T throughout life

large in males

INAH-3

human equivalent of rat SDN-POA

larger in men than women

larger in straight men than gay men

spinal nucleus of the Bulbocavernosus muscle (SNB)

SNB motorneurons more numerous in male than female rats

Onuf’s nucleus

motorneurons more numerous in men than women

molecular sex differences in brain

expression of steroid receptors: gonadal, glucocorticoid, mineralocorticoid receptors

neuropeptide systems (ie AVP) and steroid metabolizing enzymes (ie aromatase dimorphisms in brain nuclei)

bird song brain circuitry

motor pathway: control of motor impulses to sing

auditory transmission pathway: implicated in learning

ZENK and bird song

ZENK=protein produced when birds learn new song

High Vocal Center and RA and bird song

more neurons and bigger neurons and further apart

castration of adult bird

decreased singing but no change in brain

bird brain organization

androgen treatment of F chicks masculinized size of HVC and RA but did NOT induce singing

E2 to chicks and T to adult Fs masculinized HVC and RA AND induced singing

how does bird song work

organized by estrogens first after hatching then activated by testosterone in adulthood

seasonal effects in birds

seasonal change in androgens paralleled by changes in song nuclei

T implants in Fs can also induce changes

teleost fish

3 sexual phenotypes

tree shews organization

peripubertal surge in T causes more territorial marking and male scented odors

2 processes of human organization

gonadal maturation

behavioral maturation

human behavioral changes

sexual stimuli salience

sexual motivation changes

sexual performance

4 levels of analysis to bird song

Proximate- T levels rise and stimulate

Developmental- exposure to steroid hormones during development grows song system

Ultimate- singing helps the male protect his territory and attract mates

Evolutionary history- the history of singing behavior as we go back through bird history

IUP effects on mice and hamsters

aggression higher in females next to more brothers

female typical sexual behavior lower in females next to more brothers