Metatheria (marsupials)

Marsupials: kangaroo Wombat Wallaby Koala Marsupial wolf

Our friend, the opossum only marsupial in north america Young tiny at birth (0.16 g) Attach to nipples in pouch (marsupium) 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 leaves Average life span in the wild:20 years Size:23.5 to 33.5 in Weight:20 lbs Protection status: Threatened.

Bandicoot/Billby Over 40 species Diet: omnivore Lifespan: 2-3 years Size: 7-14 inches 1-3 pounds All species are endangered

Tasmian Devil Diet: Carnivore Lifespan: 5 years Size: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