Lyons and Lourdon Flashcards
Polygamy
Male has more than 1 female mate
95% of mammalian species
Why is polygamy the major mating system
evolution of pregnancy and lactation means reproductive costs largely on female
What is the gonadorophin axis?
Brain (decapeptide) –> LH and FSH in pituitary gland –> Gonads –> behaviour
What are the principles of the neuroendocrine system (BRAIN)?
- produces low mol. weight peptides which act in anterior pituitary to release larger glycoprotein hormomes
- hormones of posterior pituitary secreted from nerve terminals in hypoT.
- many of these hormones also act via other pathways in the brain
What are the principles of the neuroendocrine system (Gonads)?
Produces sex steroids:
- act locally to regulate gonadal function
- act on body to differentiate development and physiology
- act on brain to regulate behaviour
How do peptides function in neuroendocrine system?
- peptides from the brain act on peripheral physiology via pituitary gland
- they also act directly on brain behaviour
- peptides involved in specific physiological function also act on sexual behavioural pathways in the CNS
What does GnRH control and how?
- GnRH causes release of LH and FSH
- sex steroids and gonadal peptides feedback to regulate pituitary activity
- GnRH also acts directly on brain and facilitates lordosis behaviour in females when injected
THEREFORE - peptide controls both pituitary gonadotrophins & sexual behaviour
What is lordosis, which hormone facilitates it?
characteristic sexually receptive behaviour in female rodents
- occurs in certain stage of oestrous cycle
- cannot exhibit without ovaries
- Oestradiol
How is the brain masculinesed?
- the brain is female by default
- oestrogen causes masculinisation of male brain and sexual dimorphism, but not in women
- BECAUSE, there is a short window of opportunity
- ovaries produce 100x less test than testis
What is the Aromatisation hypothesis?
- Aromatised oestrogen metabolites of testosterone masculinses the brain in the hypothalamus
- AFP system ‘swamped’ by oestrogen injection
- doubts over its validity
What does testosterone do?
Effects the brain, libido, deepens voice, increases lean muscle mass, male sex organs
How does testosterone secretion effect hormomes?
Developing testis secrete test, stimulates Wolffian Duct Formation & Mullerian Inhibiting Hormone, which causes Mullerian duct to generate leading to the absence of a uterus
What is the Jost hypothesis?
secretion of androgens & MIH by foetal testis during critical stages of development accounts for full range of sexually dimorphic urogenital traits observed at birth
MIH
Mullerian Inhibiting Hormone (MIH/AMH) is large molecularly, TGH-ß super family
How is gender determined in mammals?
- small region on tip of Y, location of SRY gene which is sex determining part
- SRY switches on sertoli cells in gonad, differentiating them
- they can support germ cells, and they stimulate development of Leydig cells
What do Leydig cells do
make testosterone
What do Sertoli cells do
- secrete substance initiating meiosis
- secrete testicular fluid
- conc. test locally
- release MIH
- protext spermatids from immune system
Castrate
XY:
- lack of androgen effect on long bone growth
- small penis, no body hair
- pubic hair originates from adrenal glands
Klinefelters
XXY:
- Small testis, low testosterone, limited breast development
- no spermatozoa produced (XXY cells don’t survive outside testis)
- scant body hair
XY digenesis
XY:
- X-linked supressor of SRY
- Male karyotype, undevelopeed female appearance
- no testi development, ovaries develop then degenerate
- normal vagina
- no ovaries = no sex steroids, no pubes/breasts
- tall
- ‘tall freak with vagina’
Testicular feminisation
XY:
- no androgen receptor
- testicular oestrogen drives breast development
- voluptous breasts, no testosterone signal opposing oestrogen
- MIH prevents uterus formation
- intra-abdominal testes as body can’t read test. signal
- short, blind-ending vagina
- raised as girls
Turner’s syndrome
XO:
- X missing
- ovaries or steak gonads
- Mullerian ducts present (no testis, no MIH)
- Wolffian duct absent (no test)
- Lack of germ cells = lack of sex steroid production
- no breasts, thick neck, socially awkward
Guevedoces
- raised girls
- puberty –> test rises to sufficient levels to virilise body
- testis descent, penis develops and grows
- cannot synthesis 5a-DHT because of mutation
5a-DHT
essential substrate of testosterone, far more potent
why is hyena mating difficult?
- female has peniform clitoris
- clitoris has to rupture female retractor muscles
- high neonatal and perinatal mortality
- distance of vagina to cervix huge
- pup can lodge in peniform clitoris
Reason for sexual mimicry?
- Social dominance
- Sperm fitness and selection
- Competition aggression hypothesis
sexual dominance
- genital sniffing part of social greeting - behaviour
- male infanticide? female aggression?
- problem = does this compensate for high reproductive cost of masculinised external genetalia?
sperm fitness and selection
- females highly promiscuous and polyandrous
- advantage = complex sex promotes sperm selection
- problem = hyenas testes small and oestrous cycle suggests not
Competition aggression hypothesis
- intense competition for food
- polyandrous means bigger females
- females also more aggressive, in charge of everything
- could masculinised genetalia be a by product of this?
Advantages of hyenas sexual mimicry
- females size masculinsed behaviour promotes mother’s enhanced status
- essential to support energetic demands - lactation and parental care
Disadvantages of hyeneas sexual mimicry
- pseudopenis starts development before foetus is exposed to androgens
- therefore pseudopenios can be bi-product of enhanced androgen exposure
What does the Hyena’s placenta do?
Converts ovarian androstenedione to testosterone via high levels of hydroxysteroid dehydrogenase
How is mammals sex determined?
X inactivation
how is bird sex determined?
- females are heterogametic, mechanism for sex determination unknown
- DMRT1 is candidate switch gene
What does DMRT1 do
Candidate switch gene in birds
- 2 doses for males
- 1 for females
how does showy plumage come about?
- not result of masculinisation by test
- develops as a consequence of chromosomal sex
- ZZ male, ZW female
- OESTROGEN CRUCIAL
Why do male birds sing and females chatter?
- due to oestrogen promoting axonal growth of RA region, masculinises song circuitry
what does castration in birds prove?
castration does not block sexually dimorphic development, therefore birds must get oestrogen from elsewhere (Brain)
gyandromorph
- rare, two embryos fuse = lateralised dimorphism
- not just plumage
- not in mammals
- ## female one side, male the other
Platypus?
mammal physiology, reptilian/bird sex determination
evidence for marsupial sex determination
- embryonic diapause
- males have scrotum and testis, females pouches and mammary glands
Embryonic diapause?
marsupials have it –> lactation induced negative feedback. wont be fertile until after breastfeeding stops
How does chromosomes effect sex in marsupials
X = no pouch but a scrotum
XX = no scrotum, but a pouch & mammary gland
TSD
temperature-dependant sex determination
alligators, turtles, tuataras
features of TSD
- all have same karyotype
- in alligators, 100% male at high temperature and window (21-28 days)
- known as thermos-temporal regulation
- elegant way of matching population to available resources
- no sex chromosomes
mechanism of TSD
- oestrogen
- aromatisation of testosterone to oestrogen is crucial
- oestrogen activates female pattern development
- blockade of oestrogen leads to male
- OESTROGEN CORE COMPONENTA
primary sexual characteristics
uterus, vagina, penis
secondary sexual characteristics
during or after puberty
pubic hair, voice deepens
Sperm competition
female mates with many males (promiscuous) in one cycle
Results in huge testis and abundance of sperm
gorilla mating
- Harem (3/4 females)
- small testis
- small window to copulate
chimp mating
- promiscuous
- big testis
Colour in primates
- most colourful mammals
- vision is key, at expense of olfaction
- colour is badge
- mandrills increase colour with rank increase (and testosterone)
How do females advertise fertility
oestrous swelling
Talk about primates spermatozoa
- size of mid piece is related to social mating structure in primates
- Midpiece comprises densely packed mitochondria and energy in the absnece of glycolytic support
- mitochondrial loading associated with motility and flagellum motility
