And looking beyond mammals, forms of placentation are found in everything from lizards, to seahorses, to insects, and preliminary studies indicate that many of the genes or traits involved are shared Ostrovsky et al.
It will be fascinating to learn how deeply we can trace the origins of the pregnancy toolkit. This article is distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use and redistribution provided that the original author and source are credited. Article citation count generated by polling the highest count across the following sources: Crossref , PubMed Central , Scopus.
Lactation is necessary for both infant and fetal development in eutherians and marsupials, although marsupials have a far more complex milk repertoire that facilitates morphogenesis of developmentally immature young.
In this study, we demonstrate that the anatomically simple tammar placenta expresses a dynamic molecular program that is reminiscent of eutherian placentation, including both fetal and maternal signals. Further, we provide evidence that genes facilitating fetal development and nutrient transport display convergent co-option by placental and mammary gland cell types to optimize offspring success.
Many developmental functions in marsupials and placental mammals are accomplished by different tissues, but similar genes. Cited 2 Views 5, Annotations Open annotations.
The current annotation count on this page is being calculated. Cite this article as: eLife ;6:e doi: Figure 1. Download asset Open asset. Langer P The phases of maternal investment in eutherian mammals Zoology — Evolution 69 — Marsupial reproduction: the choice between placentation and lactation, Oxford Reviews of Reproductive Biology, Vol.
Version of Record published: September 12, version 1. A two-part list of links to download the article, or parts of the article, in various formats. And humans, of course, are also placental mammals.
Placental mammals all bear live young, which are nourished before birth in the mother's uterus through a specialized embryonic organ attached to the uterus wall, the placenta. The placenta is derived from the same membranes that surround the embryos in the amniote eggs of reptiles, birds, and monotreme.
The term "placental mammals" is somewhat of a misnomer because marsupials also have placentae. As a result, the fetus can become large and mature before birth. This increases its chances of surviving. On the other hand, supporting a growing fetus is very draining and risky for the mother.
The mother has to eat more food to nourish the fetus. She also becomes heavier and less mobile as the fetus gets larger. As a result, she may be less able to escape from predators. Giving birth to a large infant is also risky. Is this kangaroo a placental mammal? Therian Mammals Like other female vertebrates, all female mammals have ovaries. The uterus plural, uteri is a pouch-like, muscular organ.
The embryo or fetus develops inside the uterus. Muscular contractions of the uterus push the offspring out during birth. The vagina is also where the male deposits sperm during mating. Placental Mammals Placental mammals are therian mammals in which a placenta develops during pregnancy. The Placenta The placenta is a spongy structure. Pros and Cons of Placental Reproduction The placenta permits a long period of fetal growth in the uterus.
Summary Therian mammals are viviparous. They give birth to an embryo or infant rather than laying eggs.
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