海龜可以部分控制自己的性別

海龜可以部分控制自己的性別

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.

對于某些種類的海龜來說，性別決定是一種選擇自己的冒險。未孵出的海龜在蛋里四處走動，它們的行動可以決定，當它們從殼里掙脫出來時是雄性還是雌性。這一事實可能會改善某些物種因全球變暖導致性別比例失衡而瀕臨滅絕的前景。

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.

哺乳動物，除了少數(shù)例外，大部分是通過染色體來決定性別的。盡管一些爬行動物也會這么做，但對于其他爬行動物來說，性別取決于孵化的溫度，而一些種類的爬行動物則會以更復雜的方式把事情混在一起。然而，即使性別是基于溫度的，似乎我們也只是剛剛解決了問題的表面。

"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."

中國科學院的杜衛(wèi)國教授在一份聲明中說:“我們之前證明了爬行動物的胚胎可以在卵內(nèi)移動來調(diào)節(jié)體溫。所以我們很好奇這是否會影響他們的性別決定。”

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.

杜教授在實驗室和室外環(huán)境中孵化了淡水龜毛雷米·里維斯的卵。他發(fā)現(xiàn)，在一天的高峰期，龜?shù)耙欢伺c另一端之間的溫差可能高達4.7攝氏度(8.5華氏度)，成為雄性或雌性的幾率大概相差兩倍多。

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.

雖然從理論上講，這意味著海龜可以通過移動到蛋的較暖或較冷的一端來影響自己的性別，但杜教授需要進行干預，看看這是否真的發(fā)生了。在《當代生物學》(Current Biology)雜志上，他描述了使用化學物質(zhì)“辣椒堿”，這種物質(zhì)會干擾爬行動物感知一半蛋殼溫度的能力，從而降低對溫度的反應。

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.

在涼爽的月份，經(jīng)辣椒堿處理的蛋都孵化成雄性，而在炎熱的月份，幾乎都是雌性。然而，在沒有經(jīng)過辣椒堿處理的蛋中，這一比例幾乎是兩倍。然而，辣椒堿對總生存率沒有顯著影響。

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.

這些發(fā)現(xiàn)有助于解釋，在過去氣候發(fā)生巨大變化的情況下，利用依賴溫度的性別決定的物種是如何存活下來的。人們還認為，海龜會在陰涼和陽光充足的抓握部位之間轉(zhuǎn)移，并隨著環(huán)境的變化，慢慢進化出不同的溫度范圍。

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.

杜認為，這一效應意味著，全球變暖導致的某些物種間的性別失衡可能并不像之前擔心的那么糟糕。有警告稱，到2100年，佛得角群島上只有0.14%的紅海龜能孵化出雄性紅海龜，這是一個非常好的消息。然而，這篇論文警告說，根據(jù)殼內(nèi)的溫度梯度，以及在胚胎能夠移動之前，殼的有效移動程度是有限的。