Janzen Fredric J
Department of Ecology and Evolution, University of Chicago, Chicago, Illinois, 60637.
Evolution. 1995 Oct;49(5):864-873. doi: 10.1111/j.1558-5646.1995.tb02322.x.
The evolutionary significance of sex-determining mechanisms, particularly temperature-dependent sex determination (TSD) in reptiles, has remained unresolved despite extensive theoretical work. To investigate the evolutionary significance of this unusual sex-determining mechanism, I incubated eggs of the common snapping turtle (Chelydra serpentina) at a male-producing temperature (26°C), a female-producing temperature (30°C), and an intermediate temperature that produced both sexes about equally (28°C). Laboratory experiments indicated that two performance variables, but no morphological measurements, were significantly influenced by incubation temperature (P ≤ 0.05): hatchlings from cooler incubation treatments swam faster than turtles from warmer incubation treatments, and hatchlings from 28°C exhibited a greater propensity to run than did individuals from 26°C and 30°C. In the field, hatchlings from the all-male and all-female producing temperatures had significantly higher first-year survivorship than did consexuals from the incubation temperature that produced both sexes (G = 6.622, P = 0.03). Significant directional selection was detected on propensity of hatchlings to run (β' = -0.758, P = 0.05): turtles that tended to remain immobile had a higher probability of first-year survivorship than did individuals that moved readily. Thus, the effects of the gender × incubation temperature interaction on survivorship of hatchling turtles observed in the field experiment may have been mediated by temperature-dependent antipredator behavior. These results provide a possible functional explanation for the evolutionary significance of TSD in turtles that is consistent with predictions of theoretical models.
尽管有大量的理论研究，但性别决定机制的进化意义，尤其是爬行动物中依赖温度的性别决定（TSD），仍未得到解决。为了探究这种不寻常的性别决定机制的进化意义，我将普通鳄龟（Chelydra serpentina）的卵分别在产生雄性的温度（26°C）、产生雌性的温度（30°C）以及产生两性数量大致相等的中间温度（28°C）下孵化。实验室实验表明，有两个性能变量受到孵化温度的显著影响（P≤0.05），但形态测量不受影响：来自较冷孵化处理的幼龟游泳速度比来自较暖孵化处理的幼龟快，并且来自28°C的幼龟比来自26°C和30°C的个体表现出更强的奔跑倾向。在野外，来自全雄性和全雌性产生温度的幼龟第一年的存活率显著高于来自产生两性的孵化温度下的同性别幼龟（G = 6.622，P = 0.03）。在幼龟的奔跑倾向方面检测到显著的定向选择（β' = -0.758，P = 0.05）：倾向于保持不动的幼龟比容易移动的个体有更高的第一年存活概率。因此，在野外实验中观察到的性别×孵化温度相互作用对幼龟存活率的影响可能是由依赖温度的反捕食行为介导的。这些结果为龟类TSD的进化意义提供了一个可能的功能解释，这与理论模型的预测一致。
