title: Placentation and maternal investment in mammals.
abstract: The mammalian placenta exhibits striking interspecific morphological variation, yet the implications of such diversity for reproductive strategies and fetal development remain obscure. More invasive hemochorial placentas, in which fetal tissues directly contact the maternal blood supply, are believed to facilitate nutrient transfer, resulting in higher fetal growth rates, and to be a state of relative fetal advantage in the evolution of maternal-offspring conflict. The extent of interdigitation between maternal and fetal tissues has received less attention than invasiveness but is also potentially important because it influences the surface area for exchange. We show that although increased placental invasiveness and interdigitation are both associated with shorter gestations, interdigitation is the key variable. Gestation times associated with highly interdigitated labyrinthine placentas are 44% of those associated with less interdigitated villous and trabecular placentas. There is, however, no relationship between placental traits and neonatal body and brain size. Hence, species with more interdigitated placentas produce neonates of similar body and brain size but in less than half the time. We suggest that the effects of placental interdigitation on growth rates and the way that these are traded off against gestation length may be promising avenues for understanding the evolutionary dynamics of parent-offspring conflict.
authors.affiliation: Evolutionary Anthropology Research Group, Department of Anthropology, Durham University, Dawson Building, South Road, Durham DH1 3LE, United Kingdom. isabella.capellini@durham.ac.uk
authors.forename: Isabella
authors.initials: I
authors.lastname: Capellini
authors.forename: Chris
authors.initials: C
authors.lastname: Venditti
authors.forename: Robert A
authors.initials: RA
authors.lastname: Barton
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D001835:Body Weight / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology* / Q000196:embryology; D005260:Female; D005333:Fetus / Q000033:anatomy & histology / Q000196:embryology / Q000502:physiology; D008322:Mammals / Q000033:anatomy & histology* / Q000196:embryology / Q000254:growth & development / Q000502:physiology*; D008954:Models, Biological; D009929:Organ Size; D010802:Phylogeny; D010920:Placenta / Q000033:anatomy & histology* / Q000502:physiology*; D010929:Placentation; D011247:Pregnancy