Infra-class Metatheria

The taxonomy, life history, & ecology of:

Marsupials

“animals with pouches”

But first...

Prototheria (4 species) = egg-laying monotremes Theria = live birth Metatheria (~280 species) = viviparous Eutheria (~4500 species) = placental birth

P ro to th e ria

E u the ria M e ta th e ria

T h e ria

M a m m a lia

Luo, Z. 2007. Transformation and diversification in early mammal evolution. Nature, 450, 1011-1019.

7 Orders (18 families):Didelphimorphia (American opossums)Paucituberculata ("shrew" opossums)Microbiotheria (monito del monte & extinct relatives)Dasyuromorphia (Australasian carnivorous marsupials)Peramelemorphia (bandicoots and bilbies)Notoryctemorphia (marsupial "moles")Diprotodontia (kangaroos, wallabies, possums, koalas, gliders, wombats, etc)

*Two primary divisions within Marsupialia denote American marsupials and Australian marsupials.

Adaptive Radiation

largest

smallest

Fossil Evidence Suggests Marsupials Much More Common

Marsupial origination is cited as Mongolia

Advantages of placental development must have out-competed marsupial

Australia has maintained diversity and dominance of marsupials because of isolation

Distribution of Metatheria

Virginia Opossum Only Marsupial in North

America Very generalized Immune to rabies Can remain in involuntary

comatose state for 1min. – 6 hrs. 13day gestation, when

born size of honeybee More teeth than any other

NA land mammal = 50

Convergent Evolution

Filling the same ecological niche in diff. parts of the world.

Seperated from common ancestor 100-150mya

Marsupials still maintain diversity and dominance in Australia

Burrowing

Flying squirrel,Arboreal placental

Marupial (left)Antechinus stuartii

Placental (right)Peromyscus maniculatus

Similar Habits

Placental: Golden mole of S. Africa

Marsupial mole of Australia

Flying Foregut Fermentation

Sugar gliderarboreal marsupials.

Termite eating

Numbat (above)Anteater (right)

Metatheria are different because…

Development Ecretory/reproductive systems Cranial differences Epipubic bone Teeth

Teeth Different number of incisors on top and bottom P3/3, M4/4 Delayed development of teeth The milk teeth are represented by a single premolar in each

jaw Only replace one tooth postnatally

Reproduction & Development

Short gestation (8-43 days) Young born extremely small relative to adult

size Organs not completely developed Well-developed front limbs for grasping fur Move to pouch or (if pouchless)

grab ahold of teats

Newborn Kangaroo 0.003% mother’s weight

Teat swells in its mouth to make a semi-permanent attachment

Stays in pouch for 1 week - 1 year Leaves pouch at weight roughly

equivalent to birthweight of a similarly-sized placental

Milk changes composition during lactation Early: high protein, low fat (for structural development) Later: low protein, high fat (for rapid increase in mass)

Major investment during Lactation

Marsupial vs. PlacentalCharacter Marsupial state Placental state

Diversity 6% of living mammal species 94% of living mammal speciessize not as large larger range of body sizesstructural adaptations less diverse flying (wings), marine (fins)

Reproduction[Figs. 10.7]

brief gestation; semiembryonic young; body mass 1% of mother [Fig. 10.11]. Need for precocious grasping forelimbs may constrain adaptability

long gestation period; young more developed at birth; body mass up to 50% of mother

Placenta [Fig. 9.11] choriovitelline (usually)  chorioallantoicLactation period [Fig. 10.7]

long short

Investment of energy in motherhood

lower, altricial younghigher, reproduce more rapidly (usually), precocial young

Cerebral Cortex/ Braincase

smooth and complex, slow development, smaller volume (maybe)

fast development, greater volume (maybe)

Behavioural plasticity uncommon great range of behavioursTerritoriality uncommon common and important

Antipredator behaviour not well developedhighly developed, particularly in herding animals; capable of sustained high speeds

Epipubic bones present absentBaculum [Fig. 9.3] absent present in mostAuditory bullae derived from alisphenoid bone varies, but not alisphenoid

primitive dental formula 5/4-1/1-3/3-4/4 3/3-1/1-4/4-3/3

Common bushtail possum

TOPAvg. weight gain much greater in younger possums suggesting older mothers put put more effort into reproduction than maintenance/survival

MiddleSurvival to breed the following year. Notice year 5 - ??

BottomMean Reproductive Effort measured as relative mass lost during lactation

*Terminal Reproductive Hypothesis exemplified in Marsupials

Isaac, J.L. & Johnson, C.N. 2010. Terminal reproductive effort in a marsupial. Biology Letters. 1: 271-275.

RE as loss of weight shows transfer of energy protrayed in yearling weight.

Theoretical Constraints of Lactation

Young have limited control over energy input - Marsupial mammary gland is relatively unresponsive to changes in suckling

In placental animals, fetal hormones control more energy transfer

Mother-offspring conflict constrains adaptive variation

Sources http://www.biology.iastate.edu/InternationalTrips/1Australia/04papers/keuderDigSys.htm http://users.tamuk.edu/kfjab02/Biology/Mammalogy/systematics/A1metatheria.htm http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html http://users.tamuk.edu/kfjab02/Biology/Mammalogy/systematics/A1metatheria.htm http://animaldiversity.ummz.umich.edu/site/accounts/information/Metatheria.html Google Images

Tyndale-Biscoe, H. 2005. Life of Marsupials.