海龟可以部分控制自己的性别

海龟可以部分控制自己的性别

Sex determination is a choose-your-own-adventure for some species of turtles. Unhatched turtles move around within their eggs, and their movements can determine whether, when they do break free from their shells, it will be as male or female. The fact may improve the prospects of some species in danger of extinction from global warming skewing their sex ratios.

对于某些种类的海龟来说，性别决定是一种选择自己的冒险。未孵出的海龟在蛋里四处走动，它们的行动可以决定，当它们从壳里挣脱出来时是雄性还是雌性。这一事实可能会改善某些物种因全球变暖导致性别比例失衡而濒临灭绝的前景。

Mammals, with somewhat rare exceptions, determine sex through chromosomes. Although some reptiles do the same, for others sex is based on the temperature at which the incubation takes place, while a few species manage to mix things up in even more complex manners. However, even where sex is based on temperature, it seems there are still some wrinkles we are only just working out.

哺乳动物，除了少数例外，大部分是通过染色体来决定性别的。尽管一些爬行动物也会这么做，但对于其他爬行动物来说，性别取决于孵化的温度，而一些种类的爬行动物则会以更复杂的方式把事情混在一起。然而，即使性别是基于温度的，似乎我们也只是刚刚解决了问题的表面。

"We previously demonstrated that reptile embryos could move around within their egg for thermoregulation,” said Professor Wei-Guo Du of the Chinese Academy of Sciences in a statement. “So we were curious about whether this could affect their sex determination."

中国科学院的杜卫国教授在一份声明中说:“我们之前证明了爬行动物的胚胎可以在卵内移动来调节体温。所以我们很好奇这是否会影响他们的性别决定。”

Du incubated the eggs of Mauremys reevesii, a species of freshwater turtle, in both laboratory and outdoor settings. He found the temperature difference from one end of an egg to the other could be a remarkable 4.7ºC (8.5ºF) at the peak of the day, more than double the width of the band in which the probability of being male or female is approximately even.

杜教授在实验室和室外环境中孵化了淡水龟毛雷米·里维斯的卵。他发现，在一天的高峰期，龟蛋一端与另一端之间的温差可能高达4.7摄氏度(8.5华氏度)，成为雄性或雌性的几率大概相差两倍多。

While theoretically, this means turtles could influence their sex by moving to the warmer or cooler end of the egg, Du needed to intervene to see if this really happens. In Current Biology he describes applying the chemical capsazepine, which interferes with reptiles’ capacity to sense temperature to half the eggs, reducing movements in response to temperatures.

虽然从理论上讲，这意味着海龟可以通过移动到蛋的较暖或较冷的一端来影响自己的性别，但杜教授需要进行干预，看看这是否真的发生了。在《当代生物学》(Current Biology)杂志上，他描述了使用化学物质“辣椒碱”，这种物质会干扰爬行动物感知一半蛋壳温度的能力，从而降低对温度的反应。

In a cool month, batches of capsazepine-treated eggs all hatched as males, while in a hot one almost all were female. However, among the non-capsazepine eggs, the ratio was close to even both times. Capsazepine treatment made no significant difference to overall survival, however.

在凉爽的月份，经辣椒碱处理的蛋都孵化成雄性，而在炎热的月份，几乎都是雌性。然而，在没有经过辣椒碱处理的蛋中，这一比例几乎是两倍。然而，辣椒碱对总生存率没有显著影响。

The findings help explain how species that use temperature-dependent sex determination have survived large changes in climate in the past. Turtles are also thought to have shifted between shaded and sunny clutching sites and slowly evolved different temperature ranges in response to changing conditions.

这些发现有助于解释，在过去气候发生巨大变化的情况下，利用依赖温度的性别决定的物种是如何存活下来的。人们还认为，海龟会在阴凉和阳光充足的抓握部位之间转移，并随着环境的变化，慢慢进化出不同的温度范围。

Du calculates this effect means the sexual skew induced by global warming among some species may not be as bad as previously feared. In the light of warnings that just 0.14 percent of loggerhead turtles in the Cape Verde Islands would hatch male by 2100, that’s very good news. However, the paper cautions there are limitations on how effective shell movements can be, depending on the temperature gradient within the shell, and how hot it gets before the embryo can move.

杜认为，这一效应意味着，全球变暖导致的某些物种间的性别失衡可能并不像之前担心的那么糟糕。有警告称，到2100年，佛得角群岛上只有0.14%的红海龟能孵化出雄性红海龟，这是一个非常好的消息。然而，这篇论文警告说，根据壳内的温度梯度，以及在胚胎能够移动之前，壳的有效移动程度是有限的。