The 3 subclasses of mammals differ strikingly in their modes of reproduction

Prototheria (monotremes) Metatheria (marsupials)

Eutheria (placentals)

Monotremes: Unique Reproduction

1) Lay eggs

2) Cloaca

3) No nipples

                         

Unique Features of Monotreme Reproduction

• 1. Ovaries larger (relative to body size) than other mammals

• 2. Oviducts open into urogenital opening called a cloaca, similar to reptile cloaca (meaning of name “monotreme”)

• 3. Milk secreted by glands in skin, licked from tufts of fur at concentrations of glands

• 4. Young have “egg tooth” like birds to help break out of egg

• Platypus: 1-2 eggs

• Echidna: 1 egg

How can a mammal lay an egg????

• Monotreme egg? • Reptile egg?

More evidence of evolution:

Typical platypus reproduction:

Egg is fertilized in fallopian tubes before entry to uterus, eventually coated with leather mineralized shell before being laid.

Egg at fertilization = 4 mm, when laid = 12 mm.

Egg retained in uterus about 28 days while development proceeds. THEN shell added, egg laid, 10 more days of external incubation. (Eggs sticky, female cradles between stomach and tail.)

Lactation about 3-4 months.

Platypus:1.Low body temperature around 90 degrees farenheit2.Living species of platypus lack teeth3.Only found in Australia4.Baby platypus’s is called a puggle5.Small approximately 20 inches and 3 pounds6.Eat insects and crustaceans using their sensitive bill to Locate their prey.7. Use front feet to swim, steer with tail and backfeet

Monotremes: echidnasOnly 1 egg, incubates in a pouch where hatching occurs.

4 species of echidnas: also called spiny ant eaters

Located in Australia

Lactation for about 4 months more.

http://animal.discovery.com/videos/fooled-by-nature-spiny-anteater.html

Metatheria (marsupials)

Marsupials:

kangaroo

Koala

Wallaby

Wombat

Marsupial wolf

Our friend, the opossum only marsupial in north america1) Young tiny at birth (0.16 g)

2) Attach to nipples in pouch (marsupium)

3) Short gestation, longer lactation

Opossum:

Mating season, January – July, 1-2 litters depending on latitude.

Egg fertilized in fallopian tubes, also surrounded by a shell membrane (soft) at that time.

Gestation (about 8 days).

Last 1/3 of gestation (4 days), membrane shed, eggs sink into depressions in uterine wall (has a kind of placenta, but no firm implantation), absorbs nutrients and embryos continue to grow.

Gestation totals about 12-13 d.

7-9 young make it to suckling stage.

Lactation continues to a total of about 95-105 days.

Rarely live longer than 18 months. In wild, maximum known lifespan was 3 years.

Females often get just 1 breeding season.

Some differences (from placentals) found in marsupials

• Eggs slightly larger than in placentals (0.12-0.28 mm vs 0.07-0.15 mm)

• Young never larger than about 1 g, no matter size of mother

• Gestation always short as or shorter than length of estrus cycle

• No placenta

• Many have pouch, but some only have folds of skin, and a few don’t have anything

Differences in female reproductive tracts:Label The Diagram

Size difference in Monotremes and Marsupials compared to placental mammals

Gestation versus lactation

What does this graph show?

Marsuipals compared to placental mammals of the same size have Shorter Gestation (time in the womb) However, longer Lactation time ( time nursing the offspring)

What does this data mean?

Overall Marsuipals take longer to grow their offspring compared to Placentals

Another way to look at this...

Time: conception to weaning

Takes marsupial longer than placental to raise young to same size (weaning age)

So, which is “better?”Costs:Lactation is most energetically costly period of reproduction, and less efficient means of energy transfer to young. Probably costs them a bit more in terms of time and energy.

Constraints: Newborn marsupials need to be able to crawl to pouch or teat, suckle, breathe, digest. But no wings, hooves, or flippers!

Flexibility:Marsupials in individual offspring at time of birth, can adjust litter sizes, etc.

Placental vs. marsupial morphology:

Australian Marsupials:

Over 140 species:Most are threatened due to

Red Kangaroo:Diet: Herbivore

Average life span in the wild:Up to 23 years

Size: 3.25 to 5.25 ft

Weight:200 lbs

Group name:Mob

Can reach speeds up to 35 mph and jump over 6 feet

Diet: Lives on eucalyptus leavesAverage life span in the wild:20 yearsSize:23.5 to 33.5 in Weight:20 lbs Protection status: Threatened.

Bandicoot/BillbyOver 40 speciesDiet: omnivoreLifespan: 2-3 yearsSize: 7-14 inches 1-3 poundsAll species are endangered

Tasmian DevilDiet: CarnivoreLifespan: 5 yearsSize:20 to 31 in Weight:9 to 26 lbs Protection status:Endangered

The Amazing Antechinus!

All females give birth within a few days each year.

In late Sept, shortly after females mate, all males die!

Semelparous: only 1 reproductive period per lifetime

Iteroparous: multiple reproductive events per lifetime