Transcript Marsupial developmental constraints

5 1 3 4
________
4 1 3 4
= 50
3-5
1 4-5 3
__________
3-4 1 4-5 3
= 44-54
Marsupial – Eutherian differences
Trophoblast and Placenta
Trophoblast
(eutharians only)
Chorio-vitelline
Placenta
(most marsupials)
Chorio-Allantoic
placenta
(eutharians)
Costs of pregnancy vs. lactation
Offspring: number vs. size
Marsupial reproduction &
developmental constraints
Neonatal movement to the pouch
necessitates forelimb function
http://www.arkive.org/species/GES/mammals/Macrotis_lagotis/Macrotis_lagotis_09c.html?movietype=wmMed
Marsupial developmental constraints
from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial
shoulder girdles. Evolution 58:2353-2370
Marsupial – Placental
Forelimb development
from: Shears, K. E. 2004. Constraints on the morphological evolution of marsupial
shoulder girdles. Evolution 58:2353-2370
Marsupial female reproductive cycles
Macropod marsupials
Reproductive flexibility
MARSUPIAL-PLACENTAL CONVERGENCE
Gliders
Burrowers
MARSUPIAL-PLACENTAL CONVERGENCE
Arboreal folivores
Ant-termite feeding
MARSUPIAL-PLACENTAL CONVERGENCE
Cursorial hind limbs
MARSUPIAL-PLACENTAL CONVERGENCE
Carnivory
http://www.naturalworlds.org/thylacine/films/java/film3/film_3.htm
Thylacine vs. Dingo
ecological replacement?
AUSTRALIAN MARSUPIALS
Conservation issues
Disproportionate percentage of affected taxa are
small- to medium-sized and ground dwelling.
Omnivores & herbivores affected more than carnivores.
Multiple factors involved:
1) Changes in plant community structure due to:
a) browsing and grazing by exotic placentals
(livestock, rabbits)
b) altered fire ecology (decreased frequency and
increased severity of fires)
2) Introduced predators (dogs, cats, red fox)
3) Exotic diseases
a) Koala – sexually transmitted Chlamydia causing
infertility and other problems
b) Tasmanian Devil – facial tumor disease
c) Thylacine -- distemper virus implicated in decline
4) Direct hunting (extinction of thylacine on Tasmania)
MARSUPIAL-PLACENTAL COMPETITION
Evolutionary dominance of placentals
Predomonance of eutherians on northern continents
Contemporary Asian origin of marsupials and placentals;
more rapid spread of marsupials into southern continents
American faunal exchange (late Pliocene- Pleistocene)
Placental carnivores replaced S. American “marsupicarnivores”
Extinction of a much larger number of S. American placental
groups
Northern invasion and continued spread of didelphid marsupials
Prehistoric extinctions of Australian marsupials
Late Pleistocene extinction of most large-bodied marsupials,
possibly through human hunting or by predation/competion
from introduced dogs.
Extinctions may have been due to global climate change.
Comparable levels of extinction seen for placentals on
other continents.
Historic decline & extinction of Australian marsupials
A disproportionate percentage of historic mammal extinctions
have involved Australian marsupials. Competition from exotic
placentals has been directly implicated in some cases.
Native Australian placentals (rodents) show same dramatic
level of decline and extinction. Competition with exotic
placentals is only one of many factors endangering marsupials.