Evolution of Placentation in Eugongylini (Squamata: Scincidae): Ontogeny of Extraembryonic Membranes in Oviparous and Viviparous Species of New Zealand
James R. Stewart, Kelly M. Hare, Michael B. Thompson
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引用次数: 0
Abstract
New Zealand scincid lizards, genus Oligosoma, represent a monophyletic radiation of a clade, Eugongylini, of species distributed geographically throughout the South Pacific with major radiations in Australia and New Caledonia. Viviparity has evolved independently on multiple occasions within these lineages. Studies of Australian species have revealed that placental specializations resulting in substantial placentotrophy have evolved in two lineages. The pattern of extraembryonic membrane development of oviparous species differs from viviparous species and identical placental architecture has evolved in both placentotrophic lineages. We analyzed extraembryonic membrane development in two New Zealand species, the sole oviparous species, Oligosoma suteri, and placental development of a representative viviparous species, Oligosoma polychroma, using histological techniques. We conclude that these two species share a basic pattern of extraembryonic membrane development with other squamates. Comparisons with Australian species indicate that morphogenesis of the yolk sac of O. suteri results in an elaborate structure previously known only in Oligosoma lichenigerum with a geographic distribution on Lord Howe Island and Norfolk Island. This finding supports a close relationship between these two taxa. We conclude also that the pattern of placental development of O. polychroma is identical to that of viviparous species of Australia. The terminal placental stage for each of these lineages includes a chorioallantoic placenta and an elaborate omphaloplacenta. This level of homoplasy in placental evolution is consistent with a hypothesis that selection favors regional differentiation of the maternal–embryonic interface and that the omphaloplacenta is an adaptation for histotrophic transport.
期刊介绍:
The Journal of Morphology welcomes articles of original research in cytology, protozoology, embryology, and general morphology. Articles generally should not exceed 35 printed pages. Preliminary notices or articles of a purely descriptive morphological or taxonomic nature are not included. No paper which has already been published will be accepted, nor will simultaneous publications elsewhere be allowed.
The Journal of Morphology publishes research in functional, comparative, evolutionary and developmental morphology from vertebrates and invertebrates. Human and veterinary anatomy or paleontology are considered when an explicit connection to neontological animal morphology is presented, and the paper contains relevant information for the community of animal morphologists. Based on our long tradition, we continue to seek publishing the best papers in animal morphology.