INVESTIGADORES
CUSSAC Victor Enrique
artículos
Título:
Contributions to the Study of OviparityViviparity Transition: Placentary Structures of Liolaemus elongatus (Squamata: Liolaemidae)
Autor/es:
CROCCO, M.; IBARGÜENGOYTÍA, N. R.; V. CUSSAC
Revista:
JOURNAL OF MORPHOLOGY
Editorial:
John Wiley & Sons
Referencias:
Año: 2008 vol. 269 p. 865 - 874
ISSN:
0362-2525
Resumen:
ABSTRACT Liolaemus elongatus (Liolaemidae) is a
viviparous, mainly lecithotrophic species with placental
structures specialized for uptake of oxygen and inorganic
nutrient transport. An allantoplacenta and an
omphaloplacenta are present during early embryonic
stages (2528) and there is a moderate distension of the
uterine wall and major glandular activity in the uterine
mucosa and submucosa compared with nonpregnant
females. The uterine epithelium increases in height, first
as a growth in the height of some dispersed cells localized
in all regions of the placenta, and later as groups of
cells localized in the periembryonic and central-abembryonic
regions. At embryonic stage 39, the allantoplacenta
reaches its maximum extension around the yolk
sac. Omphaloplacenta is restricted to the abembryonic
zone, the yolk cleft limiting the newly formed isolated
vitelline mass. At more advanced embryonic stages (39
42), the blood supply to the allantoplacentas periembryonic
zone increases, matching the profuse allantoic
vascularization. At embryonic stage 42, a secondary cleft
opens in the main vitelline mass, above the first yolk
cleft, and allantoic blood vessels enter into this secondary
cleft. This secondary cleft subdivides the vitelline
mass into a large embryonic region connected to a much
smaller abembryonic region. In L. elongatus most nutritional
resources seem to be provided by the yolk that
remains attached to the newborn for 2 or 3 days as an
external supply. The embryos wet weight doubles the
weight of the decrease observed in vitelline mass. But
the dry wet diminishes, evidencing the importance of
the exchange of water and inorganic nutrients. J. Morphol.
269:865874, 2008.