Lecture 24- Reproduction in Australian mammals Flashcards
What are the basics of mammalian reproduction?
• Mammals feed their young on milk, secreted by mammary glands • The three mammal groups (monotremes, marsupials & eutherians) differ dramatically in the way they reproduce + there is some variation in structure of the reproductive tract However There is also variation WITHIN groups
What does the female reproductive system look like (generalised)?
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What are the variations in female mammal reproductive tract structure?
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What is gestation, birth and stage of development of young at birth and the length of lactation in Monotremes?
-gestation= short -birth= from egg -stage of development of young at birth= very undeveloped -lactation length= long
What is laying eggs and pouch like in Monotremes?
• Lay eggs - Hatch 10 – 14 days after laying - Platypus 1-3 eggs: female remains in burrow - Echidna 1 egg: into pouch, female active • Pouch Platypus: no, Echidna: yes
What is lactation like in Monotremes?
• No teats (milk is secreted through pores) • Lactation: - Platypus 3-4 months - Echidna 6-7 months
What is distinctive about mating in Echidnas?
-echidnas form a mating train
What happens to the Echidna young?
Left in burrow when they can thermoregulate & spines begin to form!!
Where do platypus mate?
-in water -Females dig extensive breeding burrow – up to 20m long
What is gestation, birth and stage of development of young at birth and the length of lactation in Marsupials?
-gestation= short -birth= live young, development in pouch -stage of development of young at birth= very undeveloped -lactation length= long
What is the variation in gestation among Marsupials?
Gestation: 12 – 46 days Shortest gestation: bandicoots/dunnarts Smallest young: honey possum (4 mg)
How do marsupial teat number vary with species?
-2-22 -Antechinus • Supernumerary young • Teat number: 6 to 10 = geographic variation
How does pouch life vary in Marsupials?
1-11 months
What happens to the Marsupial young after permanent pouch exit?
-May be carried on back - May be left in nest -May be “young-at-foot”
What is the Antechinus reproduction like?
• Male testosterone levels extremely high prior to and during breeding season • Males aggressive, fight, stop feeding • Prolonged and frequent copulation • All males die from stress-related conditions • Males die before females give birth – no males in population for a period • Males in captivity, deprived of mating, survive much longer
What is special about Marsupial milk?
-dramatic change in milk composition during lactation • Early: tiny young continuous sucking small mammary gland dilute milk (carbohydrates) • Late: larger young intermittent sucking large mammary gland concentrated milk (protein & fats)
What is simultaneous lactation?
-Some kangaroos & wallabies have simultaneous lactation -have a newborn and an older baby, the milk is different for each -one is in pouch one is out already -newborn= under 1g, weak, continuous sucking, dilute milk -young at foot= above 1 kg, intermittent but strong sucking, concentrated milk
What is the embryonic diapause?
• Female mates within a day of giving birth • But embryo development stops at blastocyst stage due to sucking stimulus of young already in pouch • Embryo recommences development at weaning of older young – under hormone control • One female can have 3 young at different stages at any one time (one blastocyst, one in pouch, one young at the foot) • Occurs: in most macropodids, some small possums (also some eutherians e.g. seals).
What is gestation, birth and stage of development of young at birth and the length of lactation in Eutherians?
-gestation= long -birth= live young -stage of development of young at birth= developed, may be independent -lactation length= short
What is characteristic of Eutherian reproduction?
-longer gestation, more advanced young at birth, shorter lactation (relative to gestation) -At birth, much more variation in developmental stage of young -milk composition relatively constant during lactation
What is the reproduction like in mega bats?
Compared to other small eutherians: • Slower development, gestation longer (2 – 8 months) • Litter size small: most bats: 1 young/year • Form maternity colonies before giving birth • Large young – up to 30% of female weight! • Initially: carry young, then left in nursery • Must locate own offspring among many others
What is the Marsupial vs eutherian placentation?
both have a placenta during pregnancy • Eutherians: efficient allantoic placenta (respiration, nutrition, excretion) • Most marsupials: yolk-sac placenta (highly vascularised, but less efficient) • Peramelid marsupials: yolk-sac + allantoic form
What are the key differences in reproduction between the three groups of mammals?
-Monotremes & Marsupials: lactation specialists (short gestation + long lactation) -Eutherians: gestation specialists (long gestation + short lactation) -Remember exceptions!!!
What is marsupial reproduction special in?
Marsupials once regarded as primitive/inferior BUT marsupial reproductive strategies have advantages: • Some species can have multiple young at different stages at one time • Can stop investing early if environmental conditions deteriorate • Some species have embryonic diapause – can restart reproduction quickly if environmental conditions become favourable • Highly evolved: variable milk composition throughout lactation
Is there a better way of reproducing?
All three ways of reproducing successful! • Outdated view of marsupials & monotremes as “inferior” – comes from human and northern hemisphere perspective • Monotremes and marsupials also have highly successful reproductive strategies
