Can distinguish as an embryo between warm and cold: the Chinese Dreikielschildkröte (Chinemys reevesii).
Reading Turtle babies make themselves as comfortable and cuddly as possible in the egg, have discovered Chinese researchers: If it is too cold or too warm on one side of their dwelling, they move towards more pleasant temperatures on the other egg side. However, the small reptiles do not only want to improve their well-being: The journey in the egg may be vital for survival. And who else can claim to have had a say in defining their own gender? Turtles are ectothermic, meaning they do not regulate their body temperature through energy from metabolic processes, but with the help of the outside temperature. In the mornings, for example, they often look for a particularly sunny spot to recharge their batteries for the start of the day. At lunchtime, they switch back and forth between the sun and the shade, in order to achieve as even body temperature as possible. If they cool too much, they can not move well and are helplessly at the mercy of enemies. On the other hand, it is also not healthy to develop too high a body temperature - which can even be deadly in extreme cases.

Early practice, who wants to have enough energy later

Surprisingly, the turtles apparently do not learn this form of body temperature regulation through certain behaviors only when they are in the world, but possibly even before, suggesting a soft-shelled turtle study two years ago. Researchers had observed that unborn turtles are already moving in the egg and it seems that they always pull in the direction of a heat source. Whether this is actually a purposeful movement or whether perhaps physical changes in the egg are behind this observation has remained unclear. Thus, for example, it would be possible for the temperature differences to change the viscosity of the liquids within the ice and for the mini-turtles to drift back and forth due to currents flowing back and forth.

To clarify this, the Chinese researchers now studied Chinese Three-Tongue Turtles (Chinemys reevesii), a species that belongs to the pond turtles, which inhabits small lakes and ponds in Asia. A total of 125 eggs of the small reptiles were available to the scientists, who treated them differently for one week each: some were stored permanently at 26 degrees Celsius, the optimal temperature for the turtles, while others placed heat sources on the egg. If they were on the broadside, the eggs heated evenly to 29 degrees. On the other hand, if they were positioned at one end, this side heated up more than the other - target temperatures were 29, 30 and critical 33 degrees Celsius - which produced an overall temperature gradient in the egg. display

Nothing like the heat source!

Subsequently, the biologists used a light source behind the egg to observe where the embryo was at the beginning of the study and where it had placed itself after one week of incubation. For comparison, the researchers also included some eggs in the experiment harboring dead embryos. The result: If the egg was evenly warm, the little turtles stayed where they were. On the other hand, when the one end of the ice was heated to 29 or 30 degrees, they moved to this side - at least down to 3.5 millimeters, which is quite remarkable given the total ice length of about 35 millimeters.

However, the researchers found the behavior of the unborn child particularly interesting when the temperature was raised to 33 degrees - a threshold that is also critical in nature and in which not many turtle babies survive: In this case, the tiny animals did not move to the heat source to, but away from it. So you actively avoid too cool as well as too warm areas in the egg, concludes the team. Incidentally, the dead animals did not move at all - according to the researchers a clear indication that it is really a purposeful, active behavior and not a physical effect.

Important for the adults, absolutely crucial for the kids

This strategy makes perfect sense, comments the team. For as much as the adult animals depend on a good heat regulation - for the unborn, it is even more important. Because the temperature determines not only how well the embryo develops, how fast it grows and how well its mobility is developed later, but also its gender. One to two degrees are enough to make out the difference between a male and a female. In the test, the temperature gradient was up to 1.6 degrees - so absolutely sufficient for a sex determination.

So you might have to familiarize yourself with the idea that the embryos themselves co-determine their gender by specifically targeting specific temperature ranges in the egg, the researchers note. So far, it had been assumed that only the mothers shape the gender relationship, and that by the choice of the nesting site and the prevailing temperatures. However, one question remains unanswered: how exactly the little ones move in their eggs is completely unclear - their musculoskeletal system is, according to previous knowledge, not yet sufficiently developed in the examined stage to cover such distances.

Bo Zhao (Chinese Academy of Sciences, Beijing) et al .: Journal of the Royal Society: Biology Letters, doi: 10.1098 / rsbl.2013.0337 science.de Ilka Lehnen-Beyel

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