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Infra-class Metatheria

Infra-class Metatheria. The taxonomy, life history, & ecology of: Marsupials “animals with pouches”. Prototheria (4 species) = egg-laying monotremes Theria = live birth Metatheria (~280 species) = viviparous Eutheria (~4500 species) = placental birth. But first.

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Infra-class Metatheria

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  1. Infra-class Metatheria The taxonomy, life history, & ecology of: Marsupials “animals with pouches”

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

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

  4. 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.

  5. Adaptive Radiation largest smallest

  6. 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

  7. Distribution of Metatheria

  8. 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

  9. 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

  10. Flying Foregut Fermentation Termite eating Sugarglider arboreal marsupials. Numbat (above) Anteater (right) Flying squirrel, Arboreal placental Similar Habits Marupial (left) Antechinus stuartii Placental (right) Peromyscus maniculatus Burrowing Marsupial mole of Australia Placental: Golden mole of S. Africa

  11. Metatheria are different because… • Development • Ecretory/reproductive systems • Cranial differences • Epipubic bone • Teeth

  12. 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

  13. 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

  14. Major investment during Lactation • 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)

  15. Marsupial vs. Placental

  16. TOP Avg. weight gain much greater in younger possums suggesting older mothers put put more effort into reproduction than maintenance/survival Middle Survival to breed the following year. Notice year 5 - ?? Bottom Mean Reproductive Effort measured as relative mass lost during lactation *Terminal Reproductive Hypothesis exemplified in Marsupials Common bushtail possum

  17. RE as loss of weight shows transfer of energy protrayed in yearling weight. Isaac, J.L. & Johnson, C.N. 2010. Terminal reproductive effort in a marsupial. Biology Letters. 1: 271-275.

  18. 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

  19. 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.

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