Does low gas permeability of rigid-shelled gekkotan eggs affect embryonic development?

Autor: Andrews RM; Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. randrews@vt.edu, Thompson MB, Greene VW
Jazyk: angličtina
Zdroj: Journal of experimental zoology. Part A, Ecological genetics and physiology [J Exp Zool A Ecol Genet Physiol] 2013 Jun; Vol. 319 (5), pp. 259-67. Date of Electronic Publication: 2013 Mar 12.
DOI: 10.1002/jez.1790
Abstrakt: Parchment-shelled eggs are characteristic of most squamates, including the basal clades of gekkotan lizards. The majority of gekkotan lizards, however, produce rigid-shelled eggs that are highly impermeable to gas exchange; eggs are laid in dry sites and experience a net loss of water during incubation. We tested the hypothesis that the 1,000-fold lower rate of oxygen diffusion through the shells of rigid- compared to parchment-shelled eggs imposes a physiological cost on development. To do this, we contrasted species with rigid and with parchment shells with regards to (1) rates of embryonic metabolism and (2) rates and patterns of development of the yolk sac and chorioallantois, the vascularized extra-embryonic membranes that transport oxygen to embryonic tissues. Metabolic rates of embryos from the rigid-shelled eggs of Gehyra variegata did not differ from those of the parchment-shelled eggs of Oedura lesueurii. Moreover, maximum metabolic rates of gekkotans with rigid shells did not differ from those of gekkotan or scincid lizards with parchment shells. In contrast, the yolk sac covered more of the surface area of the egg at oviposition, and the chorioallantois reached its full extent earlier for the species with rigid shelled eggs (Chondrodactylus turneri, G. variegata) than for the species with parchment-shelled eggs (Eublepharis macularius, O. lesueurii). Differences in the temporal patterns of yolk sac and chorioallantois development would thus serve to compensate for low rates of oxygen diffusion through rigid shells of gekkotans.
(Copyright © 2013 Wiley Periodicals, Inc.)
Databáze: MEDLINE
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