Abstract
It is a common belief that reptile eggs should not be turned after oviposition once the embryo has attached itself to the inner membrane of the shell as it might kill developing embryos. Here, we used 338 eggs from 32 clutches of the water snake Natrix maura to (1) thoroughly describe natural clutch arrangement, (2) experimentally assess the effects of natural embryo positioning and (3) egg turning on embryo metabolism, hatching success, and hatchling phenotype. Clutches contained, on average, 59% of embryos located at the top, 28% at the bottom, and 14% on a side of the egg. Larger females laid larger clutches with higher proportion of top located embryos. Top embryos displayed higher metabolic rates (heart rates), shorter incubation time, and produced lighter and shorter snakes than bottom embryos. Egg turning did not significantly influence egg development, hatching success or hatchling phenotypes. However, post-birth mortality was significantly higher in turned (37.5%) compared to unturned (4.5%) embryos, providing support to the common belief that eggs should not be moved from their natural position.
Highlights
It is a common belief that reptile eggs should not be turned after oviposition once the embryo has attached itself to the inner membrane of the shell as it might kill developing embryos
The physical conditions experienced during incubation and the consequence for hatching success, hatchling phenotypes and overall fitness have been studied in a wide range of taxa, from birds, reptiles, fish, amphibians, to insects[1,2,3,4,5]
It is generally assumed that reptile eggs do not respond well if rolled or turned early on or after laying[18]
Summary
It is a common belief that reptile eggs should not be turned after oviposition once the embryo has attached itself to the inner membrane of the shell as it might kill developing embryos. An obvious possibility is that egg clustering/attachment may prevent the eggs from rolling during incubation, implying that the maintenance of embryo positioning within the egg volume once attached to the egg membrane is an important factor to hatching success and/or hatchling phenotypes and survival. We tested this hypothesis using eggs of the water snake Natrix maura. We thoroughly assessed the potential effects of embryo positioning and egg turning on egg development (egg mass trajectories, heart rates), hatching success, and hatchling phenotypes (body size at birth, growth rates, heart rates, behavior, and locomotor performances)
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