lecture 10: marsupial reproduction Flashcards
1
Q
What is the phylogeny of marsupials?
A
- diverged about 160 million years ago from eutherians
- marsupials do have a placenta
- offers unique opportunities to learn about how various systems evolved
2
Q
What is the diversity within marsupials?
A
Marsupial Orders
- South American (83 spp):
- Dipelphiomorpha: American opossums, 75 species
- Paucituberculata: shrew opossums, 7 species
- microbiotheridae: monito del monte, 1 species
- Australian (221 spp)
- Dasyuromorphia: native cats, marsupial mice, numbat, 68 species
- Peramelomorphia: bandicoots, bilbies, 19 species
- Diprotodonta: kangaroos, wallabies, possums, gliders, koala, wombats, 132 species
- Tarsipedidae: honey possum, 1 species
- notoryctemorphia: marsupial mole, 1 species
- total of 304 species of marsupial
3
Q
What are the south american marsupials?
A
- didelphiomorpha
- american opossums
- used quite heavily for medical studies e.g. skin cancer
- developmental biology
- sever neural pathways or spine
- microbiotheridae
- dromiciops
- not much known about it
- paucituberculata
- shrew opossums
- have paired sperm, weird, not known what the advantage is
4
Q
What are the Dasyurids?
A
- make up about .25 of australian marsupial species
- usually solitary
- most are insectivores
- big difference in size and appearance
- antechinus
- dunnart
- quoll
- numbat
- tasmanian devil
- thylacine
5
Q
What are the Diprotodonts?
A
- two front teeth
- typical iconic australian native animals
- koala
- wombat
- kangaroo
- tree kangaroo
- rat kangaroo
- potoroo
- bettong
- glider
- brushtail possum
- and the extinct marsupial lion
6
Q
What are the peramelids?
A
- marsupial moles and honey possums
- bandicoot
- bilby
- marsupial mole (pouch that faces backwards)
- honey possum (relative to its size it has the biggest testes of any mammal)
7
Q
What are the general characteristics of marsupials?
A
- many features similar to eutherians
- diversity of reproductive patterns and life-history strategies
- females
- distinctive reproductive tract
- many have a pouch
- placenta
- give birth to altricial young
- males
- scrotum is cranial to penis
8
Q
What is the female marsupial reproductive tract?
A
- fallopian tube
- ovary
- ureter
- uterus: two seperate uteri
- cervix
- (3 vaginae in total)
- lateral vagina
- median vagina
- in most marsupial species is only a transient structure
- forms just before the animal gives birth and then it regresses again
- in macropods it usually stays there
- when there is no impeding birth it just exists as a strand of connective tissue
- bladder
- urogenital sinus: common opening
9
Q
What is the marsupial male reproductive tract?
A
- male and female have similar urogenital sinus openings
- scrotum is cranial to penis
- bladder
- testes
- vas deferens
- prostate (big)
- epididymis
- cowper’s glands
- penis (bifid glans in many species)
10
Q
What is the pouch?
A
- marsupials and monotremes
- some don’t have pouches
- some only during breeding season
- supported by epipubic bones
- originally thought to support the developing pouch but now thought to support the suckling pouch young
- development is independent of hormones; XX = pouch
- pouch primordia present in male pouch young of some marsupial species
11
Q
What are altricial young in birds and mammals?
A
- altricial – “requiring nourishment”
- young that are incapable of moving around on their own soon after being born
- they are born helpless and require care for comparatively long time
- tammar wallaby born with limbs at different stages of development
- weighs half a gram at birth
12
Q
What is the neonate weight vs maternal weight?
A
- no marsupial gives birth to young that is even 1% of its body weight
- birth is not a painful process
- comparing body weights, when born a marsupial litter is 50 to 2000 times smaller than the equivalent in a eutherian
- antechinus: fucking weird breeding cycle (fight and mate and die)
13
Q
What is the tammar wallaby?
A
- Macropus eugenii
- an australian macropodid, 4 - 8 kg
- monovular, highly seasonal breeders (probably only drawback in terms of research)
- genome has been sequenced
- breeds well in captivity
- has a very well characterised breeding cycle
- timetable of developmental biology very well characterised
14
Q
What is the breeding cycle of the tammar?
A
- seasonal reproduction
- highly seasonal
- tammar’s undergo an unusual process called diapause
- give birth in mid-late jan
- within .5 - 3 hours of giving birth they go through post-partum oestrus and they mate
- the zygote develops for a couple of days and then it stops
- blastocyst in diapause
- pregnant 364 days a year
- suckling pouch young stimulates production of prolactin by the anterior pituitary
- and whilst prolactin in many species is luteotrophic, in the wallaby it is luteostatic
- this stops the development of the corpus luteum therefore no progesterone is produce, the uterus isn’t stimulated
- so the new embryo doesn’t have anything to stimulate its development → enters diapause
- if something happens to the pouch young it therefore stops suckling which reduces levels of prolactin, the CL resumes development and progesterone levels increase, uterus is stimulated to develop → diapausing embryo will resume development
- mechanism for the animal’s lifestyle
- can produce up to three babies in a season
- this is lactational diapause (montsh of jan to april)
- if the pouch young is lost after this, the embryo will remain in diapause → seasonal diapause (from about may)
- endocrinal control of seasonality
- controlled by daylength
15
Q
What are endocrine interactions in female tammar reproduction?
A
- daylight length dictates how much melatonin is produced by the pineal gland in the brain
- melatonin stimulates the production of dopamine
- dopamine acts to increase levels of prolactin which inhibits the CL
16
Q
What are the roles of prolactin in tammar?
A
- secretion ↑ in lactation and in non-breeding season in tammars
- promotes mammary development and milk secretion
- inhibits development of new corpus luteum
- prolactin → suppressed progesterone → prevents uterine development → leads to diapause
- suppression of prolactin during diapause leads to reactivated CL, uterine secretions and embryo reactivation
17
Q
What is diapause in the tammar?
A
- embryo develops to about 80 or 100 cells (diam about a quarter of a mm)
- blastocyst in diapause
- cells stop replicating
- metabolism drops
- will sit in the uterus until it gets a signal to continue development
- research about this is potentially important to understanding how to prevent cancer
18
Q
What is pre-natal tammar development?
A
- embryonic development
- look more like development in early stages unlike mouse cup-shape
- foetal development
- excellent model for studying developmental biology
- marsupials don’t have an inner cell mass
19
Q
At what stage are marsupials born?
A
- a stage equivalent to eutherian foetuses
- complete the rest of their development in the pouch
20
Q
What are features of a newborn tammar wallaby?
A
- ~400 mg, ~15mm long
- functional mesonephric kidney for 1st week after birth
- gut immature but functional
- permanently attached to teat for ~3 - 4 months
- can’t regulate its own body temperature
- eyes aren’t anywhere near being open
- completely furless
21
Q
What is tammar PY development?
A
- pouch young
- at birth the tammar’s gonads are undifferentiated
- pouch and scrotum at birht
- testis starts differentiating just after birth
- prostate buds form ~40 days
- dimorphism of phallus at 100 days
- eyes open at 150 days
- full pelage at 200 days
- females pubertal at ~280 days and can/will mate
- first birth usually doesn’t survive
- transition from ectothermic to endothermic over this time
- start to leave pouch at about day 190/200
22
Q
What is lactation in the tammar?
A
- continuously attached to teat → intermittently attached to teat → eating grass → out of pouch weaned
- 0 - 100 → 110 - 180 → 200 - 250 → 280
- lactation is pretty sophisticated
- phase 1:
- starts just before birth
- development of the mammary gland and its ability to secrete milk (also happens in eutherians)
- depends on signals from the pituitary (prolactin) and ovary (probably progesterone) and also placenta in eutherians (placental lactogen)
- ends just a couple of days after birth
- phase 2
- starts a few days after birth and ends when the young starts leaving the pouch
- don’t suddenly leave the pouch and never go back
- leave for little periods of time, have a hop around, start eating solid foods
- come back to mum for suckling and protection
- 2a (permanently attached to teat, no equivalent in eutherians) and 2b
- milk at two A is a very dilute substance high in carbohydrates because the PY can’t digest fatty acids
- reasonably high in protein
- 2b: change in composition, solids increase, switch from carbohydrates to lipids due to its change from ectothermic to endothermic
- macropods can have two suckling young at completely different stages with different milk compositions
- not known how they manage to do that - different numbers of Prl receptors
- mammary gland development is largely autonomous
- phase 3
- start leaving the pouch permanently
23
Q
Why are marsupials good models for sexual differentiation studies?
A
- they give birth to an altricial young
- most post-natal development is equivalent to the intra-uterine development of eutherian mammals
- therefore the young is accessible in the pouch during developmental stages that are only accessible in utero in other mammals
24
Q
What is sexual dimorphism in the tammar neonate?
A
- gonads undifferentiated at birth
- scrotum or mammary primordia present at birth, so sexual dimorphism occurs independently of testicular hormones
25
Q
What was vincent?
A
- intersex
- had pouch
- no scrotum
- penis
- XXY
- pouch/scrotum switch depends on number of X chromosomes, not SRY
26
Q
What is virilisation in humans and wallabies?
A
- in humans development of things such as penis, scrotum, prostate, epididymis and vas, leydig cells, testicular testosterone happen in utero way before birth
- unlike in human where presence of testosterone causes formation of all structures
- epi & VD develops first, then prostate, then penis (after scrotum which developed before birth)
- occurs after a period of time, over many weeks
27
Q
What is a new endocrine pathway to virilisation?
A
- this pathway is the main pathway in embryonic and foetal development
- via 5 alpha preganediol
- this pathway is required for sexual differentiation in humans
