Lecture 24- Reproduction in Australian mammals

Question 1

What are the basics of mammalian reproduction?

Answer 1

• 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

Question 2

What does the female reproductive system look like (generalised)?

Answer 2

-

Question 3

What are the variations in female mammal reproductive tract structure?

Answer 3

-

Question 4

What is gestation, birth and stage of development of young at birth and the length of lactation in Monotremes?

Answer 4

-gestation= short -birth= from egg -stage of development of young at birth= very undeveloped -lactation length= long

Question 5

What is laying eggs and pouch like in Monotremes?

Answer 5

• 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

Question 6

What is lactation like in Monotremes?

Answer 6

• No teats (milk is secreted through pores) • Lactation: - Platypus 3-4 months - Echidna 6-7 months

Question 7

What is distinctive about mating in Echidnas?

Answer 7

-echidnas form a mating train

Question 8

What happens to the Echidna young?

Answer 8

Left in burrow when they can thermoregulate & spines begin to form!!

Question 9

Where do platypus mate?

Answer 9

-in water -Females dig extensive breeding burrow – up to 20m long

Question 10

What is gestation, birth and stage of development of young at birth and the length of lactation in Marsupials?

Answer 10

-gestation= short -birth= live young, development in pouch -stage of development of young at birth= very undeveloped -lactation length= long

Question 11

What is the variation in gestation among Marsupials?

Answer 11

Gestation: 12 – 46 days Shortest gestation: bandicoots/dunnarts Smallest young: honey possum (4 mg)

Question 12

How do marsupial teat number vary with species?

Answer 12

-2-22 -Antechinus • Supernumerary young • Teat number: 6 to 10 = geographic variation

Question 13

How does pouch life vary in Marsupials?

Answer 13

1-11 months

Question 14

What happens to the Marsupial young after permanent pouch exit?

Answer 14

-May be carried on back - May be left in nest -May be “young-at-foot”

Question 15

What is the Antechinus reproduction like?

Answer 15

• 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

Question 16

What is special about Marsupial milk?

Answer 16

-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)

Question 17

What is simultaneous lactation?

Answer 17

-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

Question 18

What is the embryonic diapause?

Answer 18

• 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).

Question 19

What is gestation, birth and stage of development of young at birth and the length of lactation in Eutherians?

Answer 19

-gestation= long -birth= live young -stage of development of young at birth= developed, may be independent -lactation length= short

Question 20

What is characteristic of Eutherian reproduction?

Answer 20

-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

Question 21

What is the reproduction like in mega bats?

Answer 21

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

Question 22

What is the Marsupial vs eutherian placentation?

Answer 22

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

Question 23

What are the key differences in reproduction between the three groups of mammals?

Answer 23

-Monotremes & Marsupials: lactation specialists (short gestation + long lactation) -Eutherians: gestation specialists (long gestation + short lactation) -Remember exceptions!!!

Question 24

What is marsupial reproduction special in?

Answer 24

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

Question 25

Is there a better way of reproducing?

Answer 25

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