A review of the evolution of viviparity in lizards: structure,function and physiology of the placenta |
| |
Authors: | Email author" target="_blank">Michael?B?ThompsonEmail author Brian?K?Speake |
| |
Institution: | (1) Integrative Physiology Research Group, School of Biological Sciences, University of Sydney, Heydon-Laurence Building (A08), 2006 Sydney, NSW, Australia;(2) Animal Health Group, SAC, EH9 3JG Edinburgh, UK |
| |
Abstract: | The aim of this review is to collate data relevant to understanding the evolution of viviparity in general, and complex placentae
in particular. The wide range of reproductive modes exhibited by lizards provides a solid model system for investigating the
evolution of viviparity. Within the lizards are oviparous species, viviparous species that have a very simple placenta and
little nutrient uptake from the mother during pregnancy (lecithotrophic viviparity), through a range of species that have
intermediate placental complexities and placental nutrient provision, to species that lay microlecithal eggs and most nutrients
are provided across the placenta during development (obligate placentotrophy). In its commonest form, lecithotrophic viviparity,
some uptake of water, inorganic ions and oxygen occurs from the mother to the embryo during pregnancy. In contrast, the evolution
of complex placentae is rare, but has evolved at least five times. Where there is still predominantly a reliance on egg yolk,
the omphaloplacenta seems to be paramount in the provision of nutrition to the embryo via histotrophy, whereas the chorioallantoic
placenta is more likely involved in gas exchange. Reliance on provision of substantial organic nutrient is correlated with
the regional specialisation of the chorioallantoic placenta to form a placentome for nutrient uptake, particularly lipids,
and the further development of the gas exchange capabilities of the other parts of the chorioallantois. |
| |
Keywords: | Placentotrophy Lecithotrophy Embryo Nutrition |
本文献已被 PubMed SpringerLink 等数据库收录! |
|