Changes in the material properties of the shell during simulated aquatic hibernation in the anoxia-tolerant painted turtle
Changes in the material properties of the shell during simulated aquatic hibernation in the anoxia-tolerant painted turtle
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DOI：
10.1242/jeb.176990
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发表时间：
2018-09-01
影响因子：
2.8
通讯作者：
Warren, Daniel E.
中科院分区：
文献类型：
--
作者：
Odegard, Dean T.;Sonnenfelt, Michael A.;Warren, Daniel E.
西方彩龟（Chrysemys picta bellii）比任何其他四足动物都更能忍受缺氧的水下环境，在3摄氏度的环境中存活170多天。我们评估了在3℃缺氧浸泡60、130和167-170天后，漆龟骨骼的各种材料性能对缺氧浸泡60、130和167-170天后的影响，并将其与在相同温度下浸泡相同时间的正常缺氧海龟进行了比较。为了评估力学性能的变化，在三点弯曲试验中，从板上铣削梁（4x25 mm）并将其折断。分别采用微计算机断层扫描、HCO3-/CO32-滴定和电感耦合等离子体质谱（ICP-MS）测量骨矿物质密度、CO2浓度（测量骨总HCO3-/CO32-）和元素组成。在缺氧和常氧环境中越冬167 ~ 170天，骨梁的组织矿物质密度变化不显著，但与常氧环境相比，缺氧条件下骨CO2和Mg含量明显减少。在这个时间点，缺氧海龟的板梁在应力和应变下产生的应力明显小于正常缺氧海龟的板梁。当将缺氧和常氧海龟的数据放在一起时，167-170天后，与第1天采样的对照海龟相比，板梁的弹性模量减少，这表明海龟在3摄氏度的水中长时间居住而无法进入日光浴场所的影响。两组板梁的力学性能在任何较早的时间点都没有变化。我们得出的结论是，缺氧的冬眠会削弱彩龟的板层，但可能只有在持续时间超过它自然经历的时间之后。在不考虑氧合状态的情况下，水生动物越冬的持续时间可能是决定春季羽化期间龟壳力学特性的重要因素。
Western painted turtles (Chrysemys picta bellii) tolerate anoxic submergence longer than any other tetrapod, surviving more than 170 days at 3 degrees C. This ability is due, in part. to the shell and skeleton simultaneously releasing calcium and magnesium carbonates, and sequestering lactate and H(+)to prevent lethal decreases in body fluid pH. We evaluated the effects of anoxic submergence at 3 degrees C on various material properties of painted turtle bone after 60, 130 and 167-170 days, and compared them with those of normoxic turtles held at the same temperature for the same time periods. To assess changes in the mechanical properties, beams (4x25 mm) were milled from the plastron and broken in a three-point flexural test. Bone mineral density, CO2 concentration (a measure of total bone HCO3-/CO32-) and elemental composition were measured using microcomputed tomography, HCO3-/CO32- titration and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Tissue mineral density of the sampled bone beams was not significantly altered by 167-170 days of aquatic overwintering in anoxic or normoxic water, but bone CO2 and Mg were depleted in anoxic compared with normoxic turtles. At this time point, the plastron beams from anoxic turtles yielded at stresses that were significantly smaller and strains that were significantly greater than the plastron beams of normoxic turtles. When data from anoxic and normoxic turtles were pooled, plastron beams had a diminished elastic modulus after 167-170 days compared with those of control turtles sampled on day 1, indicating an effect of prolonged housing of the turtles in 3 degrees C water without access to basking sites. There were no changes in the mechanical properties of the plastron beams at any of the earlier time points in either group. We conclude that anoxic hibernation can weaken the painted turtle's plastron, but likely only after durations that exceed what it might naturally experience. The duration of aquatic overwintering, regardless of oxygenation state, is likely to be an important factor determining the mechanical properties of the turtle shell during spring emergence.