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DID EMBRYONIC RESPONSES TO INCUBATION CONDITIONS DRIVE THE EVOLUTION OF REPRODUCTIVE MODES IN SQUAMATE REPTILES?

DID EMBRYONIC RESPONSES TO INCUBATION CONDITIONS DRIVE THE EVOLUTION OF REPRODUCTIVE MODES IN... Viviparity (live-bearing) has evolved from oviparity (egg-laying) more than 100 times within snakes and lizards, and thermal factors are thought to have driven this shift. However, other major features of reptilian reproduction may reflect selective pressures related to hydric rather than thermal exchanges between the egg and its incubation environment. Notably, why are intermediate stages of prolonged egg retention so rarely seen? Embryonic stages at oviposition in squamates are largely dichotomous: most oviparous species lay eggs with embryos about one-third developed, whereas viviparous taxa retain the eggs until development is complete. Why don't more species oviposit with embryos at either earlier or later stages? We suggest that the scarcity of squamates that lay eggs soon after ovulation (and thus, with very early-stage embryos) may reflect the need to delay oviposition until embryos have developed sufficient physiological control over water influx and efflux to survive in the challenging hydric environment of the nest. The scarcity of retention to later stages (intermediate between typical oviparity and viviparity), and the apparent lack of reversals from viviparity back to oviparity, may be due to a conflict between adaptations for water versus gas exchange; retention of larger embryos in utero requires eggshell thinning to allow gas exchange, but a thinner shell precludes effective hydric control after oviposition. Thus, although the transition from oviparity to viviparity in squamates has been driven largely by thermal advantages, the clustering of species at two main positions along the oviparity-viviparity continuum may be due to challenges of controlling embryonic water balance. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Herpetological Monographs Allen Press

DID EMBRYONIC RESPONSES TO INCUBATION CONDITIONS DRIVE THE EVOLUTION OF REPRODUCTIVE MODES IN SQUAMATE REPTILES?

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Publisher
Allen Press
Copyright
The Herpetologists' League, Inc.
Subject
EVOLUTION OF VIVIPARITY IN REPTILES
ISSN
0733-1347
eISSN
1938-5137
DOI
10.1655/0733-1347%282007%2920%5B159:DERTIC%5D2.0.CO%3B2
Publisher site
See Article on Publisher Site

Abstract

Viviparity (live-bearing) has evolved from oviparity (egg-laying) more than 100 times within snakes and lizards, and thermal factors are thought to have driven this shift. However, other major features of reptilian reproduction may reflect selective pressures related to hydric rather than thermal exchanges between the egg and its incubation environment. Notably, why are intermediate stages of prolonged egg retention so rarely seen? Embryonic stages at oviposition in squamates are largely dichotomous: most oviparous species lay eggs with embryos about one-third developed, whereas viviparous taxa retain the eggs until development is complete. Why don't more species oviposit with embryos at either earlier or later stages? We suggest that the scarcity of squamates that lay eggs soon after ovulation (and thus, with very early-stage embryos) may reflect the need to delay oviposition until embryos have developed sufficient physiological control over water influx and efflux to survive in the challenging hydric environment of the nest. The scarcity of retention to later stages (intermediate between typical oviparity and viviparity), and the apparent lack of reversals from viviparity back to oviparity, may be due to a conflict between adaptations for water versus gas exchange; retention of larger embryos in utero requires eggshell thinning to allow gas exchange, but a thinner shell precludes effective hydric control after oviposition. Thus, although the transition from oviparity to viviparity in squamates has been driven largely by thermal advantages, the clustering of species at two main positions along the oviparity-viviparity continuum may be due to challenges of controlling embryonic water balance.

Journal

Herpetological MonographsAllen Press

Published: Dec 29, 2006

Keywords: Adaptation ; Embryo ; Lizard ; Oviparity ; Snake ; Viviparity

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