MARSUPIALS: The alternative therian solution The Metatherian Adaptive Zone

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MARSUPIALSThe alternative therian solution?The
Metatherian Adaptive Zone

• EEOB 625
• 16 January 2004

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Marsupial,the common name for

• 273 species, 18 families, 7 orders in
  the Infraclass Metatheria
• The alternative solution to the therian mode of
  life
• Metatheria Eutheria Separate evolutionary
  lineages since the Cretaceous

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Essential Marsupial Features

• Limited diphyodonty, i.e., only the last
• premolar (P4) is replaced (Fig. 3-9, Vaughan)
• Female reproductive tract (2 of everything)
• Choriovitelline placenta
• Short gestation long lactation
• Embryonic neonates

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Eutherian Female Reproductive Tracts
Fig. 9.9 from Feldhamer (1999, WCB McGraw-Hill
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A metatherian Female Reproductive tract
(didelphid)
Fig. 1, Harder et al. 1993
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Day 14 of gestation, the before birth
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Fig 9.11, Feldhamer
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A metatherian placenta
Fig. 14, Harder et al. 1993
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The Marsupial Mode of Reproduction How dose it
compare?

• What is the marsupial mode of reproduction?
• Is it inferior or an equivalent alternative to
  that of eutherians? Why ask? (placental
  efficiency?)
• Evidence of a competitive disadvantage for
  metherians species richness, adaptive
  radiation, and zoogeography
• Evidence from reproductive energetics

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Hsu et al. (1999)
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Non-reproductive
Fig. 1. Mean, mass-normalized assimilated
energy. Dashed line at 10 kcal mean for
non-reproductive opossums dashed line at 22
kcal non-reproductive hamsters. N 19 females
per group. Hsu et al. (1999, Fig 1)
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Hsu - Fig. 3