Substanz im Schildkrötenblut, die das Erfrieren verhindert

[gundi]

Hallo,

Es ist ja bekannt, dass europäische Landchildkröten nicht sofort erfrieren, wenn sie leichten Minus-Temperaturen ausgesetzt sind. Irgendwo habe ich gelesen, dass eine bestimmte Substanz im Blut der Schildkröte das Erfrieren verhindert bzw. hinauszögert. (Evtl. Glucose?) Wer kann mir einen Link oder Artikel nennen, der diese Frage beantwortet?
Um Missverständnisen vorzubeugen: ich habe nicht vor, meine Schildkröten in die Gefriertruhe zu packen! Es interessiert mich einfach.
Grüße
Gunda

[Ingo]

Mir ist nichts diesbezügliches bekannt.
Bei amerikanischen Szumpfschildkröten wurde viel zur Forstresistenz geforscht und auch die haben kein Frostschutzmittel:

Natural freeze-tolerance in hatchling painted turtles?

Packard GC, Packard MJ.
Department of Biology, Colorado State University, 80523-1878, Fort Collins, CO, USA. packard@lamar.colostate.edu
Hatchlings of the North American painted turtle (Family Emydidae: Chrysemys picta) typically spend their first winter of life inside a shallow, subterranean hibernaculum (the natal nest) where life-threatening conditions of ice and cold commonly occur. Although a popular opinion holds that neonates exploit a tolerance for freezing to survive the rigors of winter, hatchlings are more likely to withstand exposure to ice and cold by avoiding freezing altogether-and to do so without the benefit of an antifreeze. In the interval between hatching by turtles in late summer and the onset of wintery weather in November or December, the integument of the animals becomes highly resistant to the penetration of ice into body compartments from surrounding soil, and the turtles also purge their bodies of catalysts for the formation of ice. These two adjustments, taken together, enable the animals to supercool to temperatures below those that they routinely experience in nature. However, cardiac function in hatchlings is diminished at subzero temperatures, thereby compromising the delivery of oxygen to peripheral tissues and eliciting an increase in reliance by those tissues on anaerobic metabolism for the provision of ATP. The resulting increase in production of lactic acid may disrupt acid/base balance and lead to death even in animals that remain unfrozen. Although an ability to undergo supercooling may be key to survival by overwintering turtles in northerly populations, a similar capacity to resist inoculation and undergo supercooling characterizes animals from a population near the southern limit of distribution, where winters are relatively benign. Thus, the suite of characters enabling hatchlings to withstand exposure to ice and cold may have been acquired prior to the northward dispersal of the species at the end of the Pleistocene, and the characters may not have originated as adaptations specifically to the challenges of winter

Ich gehe davon aus, bei den Testudos sind dei Strategien ähnlich.


Gruß

Ingo

[gundi]

Herzlichen Dank, Ingo!
Obwohl ich einigermaßen Englisch spreche, ist der Text ein harter Brocken.
Ich verstehe die Kernaussagen vereinfacht so:
Es existiert kein Frostschutzmittel.

the integument of the animals becomes highly resistant to the penetration of ice into body

Die Haut wird während der ersten Lebensmonate frostresistent

the turtles also purge their bodies of catalysts for the formation of ice.

Die SK reinigen ihren Körper von Stoffen, die die Eisbildung beschleunigen (?!)

cardiac function in hatchlings is diminished at subzero temperatures, thereby compromising the delivery of oxygen to peripheral tissues and eliciting an increase in reliance by those tissues on anaerobic metabolism for the provision of ATP. The resulting increase in production of lactic acid may disrupt acid/base balance and lead to death even in animals that remain unfrozen.

Die Herzfunktion ist herabgesetzt. Der Sauerstofftransport wird unterbunden. Durch anaerobe Stoffwechselvorgänge entsteht ein Ungleichgewicht an Milchsäure, welches die Ursache dafür ist, dass die Tiere sterben, auch wenn sie nicht durchgefroren sind

Vielleicht findet ja eines Tages jemand heraus, warum in einigen Fällen Testudos ein komplettes Durchfrieren überlebt haben.

Gunda

[Beate Pfau]

Hallo Gunda,

Vielleicht findet ja eines Tages jemand heraus, warum in einigen Fällen Testudos ein komplettes Durchfrieren überlebt haben.

Für Testudo ist mir leider auch keine Untersuchung bekannt, aber vielleicht bringt Dir diese hier, an Dosenschildkröten, noch neue Erkenntnisse:

Storey, K.B., J.R. Layne, M.M. Cutwa, T.A. Churchill and J.M. Storey (1993) : Freezing survival and metabolism of box turtles, Terrapene carolina. Coeia 1993 (3) : 628 - 634. Hier das Abstract: Adult eastern box turtles Terrapene carolina carolina from Ohio readily recovered after 44 h of freezing exposure at -2 C. During thawing at 25 C, motor responses resumed in a sequence of increasing complexity with a reflex twitch in response to poking seen after 1.2 +- 0.5 h, coordinated retraction of the limbs after 2.0 +- 0.18 h, and voluntary locomotion after 2.7 +- 0.4 h. Turtles dissected immediately after freezing exposure had ice in body cavities and surrounding skeletal muscles in limbs. Analysis of putative cryoprotectants in serum and seven organs showed that all organs accumulated glucose during freezing. Net glucose accumulations of 6-20 mu-mol/g wet weight represented 4-22-fold increases; the highest glucose levels were in liver, heart, and serum. Liver glycogenolysis was identified as the source of the glucose; this was supported by both metabolite (a 62.5-fold increase in the precursor glucose-6-phosphate) and enzyme (the percentage of glycogen phosphorylase in the active a form rose from 21.3-57.5%) responses to freezing. Freezing exposure also caused an increase in lactate levels in serum and four organs, but glycerol ( lt 2 mu-mol/g), sorbitol ( lt 0.3 mu-mol/g), and free amino acid levels in organs were unchanged. Both the low levels of putative cryoprotectants and measurements of serum osmolality, 244 +- 4.3 and 315 +- 15.4 mOsmol/l for control and freezing exposed turtles, indicated that box turtles can endure freezing without an accumulation of large pools of low molecular weight cryoprotectant.

Übrigens: ich hab's nicht geschafft, mir die ganze Arbeit durchzulesen. Manche Forschung geht mir einfach zu weit.

Viele Grüße
Beate