![]() ![]() pythons, cobras 36), snakes do not care for their egg (apart from selecting for nest-site 37), and usually leave the nesting site within hours post -laying 37, 38. ![]() Pawley 35 observed no effect of “daily rotation of some Natrix natrix eggs”, and Marcellini and Davis 25 reported that egg turning did not affect hatching success in Pantherophis guttatus (results for Python molurus were unclear). Snakes appear to be the least studied group in this regard. However, experimental designs and testing techniques varied greatly across studies, making any trends difficult to characterize. In other taxonomic groups, deleterious effects have been reported, for example in the desert iguana Dipsosaurus dorsalis 31 and in most sea turtles species 32, 33, 34. No effect on egg development and hatching success were reported in the garden lizard Calotes versicolor 24, leopard geckos Eublepharis macularius 25, most freshwater turtles 21, 26, 27, 28, 29, and, to some extent, in the alligator Alligator mississippiensis 30. ![]() Thus, if the egg is turned after the embryo has attached itself, the weight of the yolk could impede normal development or tear both the vitelline and extra-embryonic membranes 18, 22, 23, leading to death or malformations 18, 21, 22, 23.Įxperimental observations about the effects of egg handling or turning in reptiles are scarce, and often anecdotic. Nevertheless, it is assumed that within a few hours after oviposition, reptile embryos rise to the top of the egg and start adhering to the inner membrane of the shell 18, 21. In the absence of specific experimental studies, whether this belief belongs to the “urban myth” category or is indeed true remains an open question. This belief most likely stems from the observation that reptilian eggs lack the avian chalazae 19, 20. in the exact same position as they were found). It is indeed common “knowledge” amongst amateur and professional reptile breeders that freshly laid eggs should be marked with a pencil to distinguish top from bottom prior to being placed in an incubator (i.e. ![]() Bird eggs benefit from turning because it facilitates embryonic development by stimulating the growth of the area vasculosa, which in turn maximizes nutrient uptake from the yolk 4.Ĭontrary to bird eggs, it is generally assumed that reptile eggs do not respond well if rolled or turned early on or after laying 18. Yet, driven by the poultry industry research and development, the role and benefits of egg rolling in birds has been extensively studied 15, 16, 17. Nevertheless, the roles played by more subtle factors such as the relative position of individual eggs within the clutch 13, 14, or the position of the embryo within the egg during incubation has attracted less attention, perhaps due to technical difficulties 4. Incubation temperature, and in relevant taxa, hygrometry, have dominated most of the research effort and proven to be paramount drivers of hatching success and hatchling phenotype 6, 7, 8, 9, 10, 11, 12. 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. 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. Egg turning did not significantly influence egg development, hatching success or hatchling phenotypes. Top embryos displayed higher metabolic rates (heart rates), shorter incubation time, and produced lighter and shorter snakes than bottom embryos. Larger females laid larger clutches with higher proportion of top located embryos. Clutches contained, on average, 59% of embryos located at the top, 28% at the bottom, and 14% on a side of the egg. 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. 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. ![]()
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