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Microparasites and placental invasiveness in eutherian mammals

Capellini, Isabella; Nunn, Charles L.; Barton, Robert A.

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Isabella Capellini

Charles L. Nunn


Placental invasiveness—the number of maternal tissue layers separating fetal tissues from maternal blood—is variable across mammalian species. Although this diversity is likely to be functionally important, variation in placental invasiveness remains unexplained. Here we test the hypothesis that increased risk of transplacental transmission of pathogens from the mother to the fetus promotes the evolution of non-invasive placentation, the most likely derived condition in eutherian mammals. Specifically, we predict that non-invasive placentation is associated with increased microparasite species richness relative to more invasive placental types, based on the assumption that higher numbers of microparasites in a population reflects greater risk of transplacental transmission to fetuses. As predicted, higher bacteria species richness is associated with non-invasive placentation. Protozoa species richness, however, shows the opposite pattern. Because invasive placentae facilitate the transfer of maternal antibodies to the fetus, we propose that the ancestral condition of invasive placentation is retained under selection for protection of newborns from higher risk of postnatal protozoan infection. Hence, our findings suggest that a tradeoff exists between protection against bacterial infection prenatally and protozoan infection postnatally. Future studies are needed to investigate how maternal prevalence of infection and the relative pre- versus postnatal risk of fetal infection by different microparasite groups vary among mammalian hosts in relation to placental invasiveness.


Capellini, I., Nunn, C. L., & Barton, R. A. (2015). Microparasites and placental invasiveness in eutherian mammals. PLoS ONE, 10(7), Article e0132563.

Journal Article Type Article
Acceptance Date Jun 16, 2015
Online Publication Date Jul 13, 2015
Publication Date Jul 13, 2015
Deposit Date Jul 8, 2015
Publicly Available Date Jul 20, 2015
Journal PLoS ONE
Publisher Public Library of Science
Peer Reviewed Peer Reviewed
Volume 10
Issue 7
Article Number e0132563


Published Journal Article (379 Kb)

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Copyright Statement
Copyright: © 2015 Capellini et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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