title: Placental morphology in two sympatric Andean lizards of the genus Liolaemus (Reptilia: Liolaemidae).
abstract: Viviparity is a remarkable feature in squamate sauropsids and it has evolved multiple times in parallel with the formation of a placenta. One example of this repeated evolution of viviparity and placentation occurs in the species-rich South American genus Liolaemus with at least six independent origins of viviparity. However, evolutionary studies of placentation in this genus are limited by a lack of data on placental morphology. The aim of this study is to describe and compare the microanatomy and vessel diameter (Dv, a function of blood flow) of the placenta using scanning electron microscopy (SEM) and confocal laser scanning microscopy (cLSM) in two sympatric Andean viviparous but highly divergent species, Liolaemus robustus and Liolaemus walkeri. We found interspecific differences in cell types in the chorion, allantois, and omphalopleure that may be explained by divergent phylogenetic history. Time elapsed since divergence may also explain the pronounced interspecific differences in vessel diameter, and within each species, there are strong differences in Dv between tissue locations. Both species show features to improve gas exchange in the chorioallantoic placenta including absence of eggshell, large Dv in the allantois (L. robustus) or embryonic side of the uterus (L. walkeri), and when present, microvillous cells in the allantois (L. walkeri). Both species also show features that suggest transfer of nutrients or water in the omphaloplacenta, including an almost complete reduction of the eggshell, secretive material (L. robustus), or vesicles (L. walkeri) on cell surface uterus, and when present specialized cells in the omphalopleure (L. walkeri). No statistical differences in Dv were found among stages 32-39 in each species, suggesting that a different mechanism, other than enhanced blood flow, might satisfy the increased oxygen demand of the developing embryos in the hypoxic environments of the high Andes.
authors.affiliation: Department of Biology and Bean Life Science Museum, Brigham Young University (BYU), Provo, Utah, 84602.|Departamento de Herpetologia, Museo De Historia Natural De San Marcos (MUSM), Av. Arenales 1256, Jesus María, Lima, Perú|Instituto de Ciencias Biologicas Antonio Raimondi, Department of Zoology, Facultad De Ciencias Biologicas, Universidad Nacional Mayor De San Marcos, Lima, Perú
authors.forename: César
authors.initials: C
authors.lastname: Aguilar
authors.affiliation: Department of Physiology and Developmental Biology, BYU, Provo, Utah, 84602.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Stark
authors.affiliation: Department of Physiology and Developmental Biology, BYU, Provo, Utah, 84602.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Arroyo
authors.affiliation: Microscopy Lab, BYU, Provo, Utah, 84602.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Standing
authors.affiliation: Departamento de Herpetologia, Museo De Historia Natural De San Marcos (MUSM), Av. Arenales 1256, Jesus María, Lima, Perú
authors.forename: Shary
authors.initials: S
authors.lastname: Rios
authors.affiliation: Department of Physiology and Developmental Biology, BYU, Provo, Utah, 84602.
authors.forename: Trevor
authors.initials: T
authors.lastname: Washburn
authors.affiliation: Department of Biology and Bean Life Science Museum, Brigham Young University (BYU), Provo, Utah, 84602.
authors.forename: Jack W
authors.initials: JW
authors.lastname: Sites
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D008116:Lizards / Q000033:anatomy & histology* / Q000502:physiology; D010920:Placenta / Q000098:blood supply / Q000648:ultrastructure*; D011247:Pregnancy; D052286:Viviparity, Nonmammalian
keywords: blood vessels; confocal microscopy; high Andes; scanning electron microscopy; viviparity