巢址选择对扬子鳄幼鳄性比的影响

The Chinese alligator(Alligator sinensis) belongs to the Temperature-dependent Sex Determination (TDS)reptile. The sex of hatchling is determined by the environmental temperature during the Temperature Sensitive Periods (TSP) of embryonic development. The eggs of the Chinese alligator are incubated in their nests, and the nest-site selection affects the temperature insdie the nest that further determines the gender of each hatchling and sex ratio of Chinese alligators. We are still not clear about what habitat features are selected by the adult Chinese alligators for nesting, how these features affect nest temperature, the occurance and duration of TSP, and how climate change may affect the hatchling sex ratio of Chinese alligators. We propose to investigate the ecological mechanisms of sex determination in Chinese alligator using multiple approaches. Our specific objectives inlcude to investigate 1) what ecological factors are related to nest-site selection, 2) how ecological factors are related to the nest temperature variations,, 3) how hatchling sex ratio variation is related to the nest temperature, 4) the time TSP of forming male and female hatchlings, and 5) the influence of climate change on the temperature insdie the nest and hatchling sex ratio.The results from this study are critical for understanding the quantitative relationship between incubation temperature and hatchling sex ratio and the TSP. The study will also help us to have better knowledge about how changes in habitat features and climate warming may affect the sex ratio and popuation dynamics in Chinese alligator and hence, to establish effective conservation strategies for this endangered species.

扬子鳄属于温度决定性别型的爬行动物。其幼鳄性别是由胚胎发育温度敏感期的环境温度所决定的。扬子鳄的卵是在巢内孵化，巢址选择会对巢内温度产生影响，进而影响到幼鳄的性别和性比。有关扬子鳄营巢会选择什么样的生境特征以及这些特征又是如何影响巢内温度，性别决定温度敏感期出现和持续的时间，以及气候变化是否会对扬子鳄后代性比产生影响等问题一直没有人进行过研究。为此我们将采用多种方法对扬子鳄性别决定的生态机制展开研究。内容包括1）影响巢址选择的生态因子，2）生态因子如何影响巢内温度变化，3）幼鳄性比变化和巢内温度的关系，4）雌雄幼鳄性别决定的温度敏感时间，5）气温变化对巢内温度及幼鳄性比的影响。研究结果对理解孵化温度与幼鳄性比间的定量关系以及性别决定的温度敏感时期至关重要。同时也有助于我们更好地认识栖息地特征变化和气候变暖对幼鳄性比及种群动态的影响，以及对这一濒危物种建立有效的保护措施。

扬子鳄的性别是由孵化温度决定，了解其自然孵化的性比，认识巢址选择对其巢内温度和后代性比的影响，特别是气候变化对其野生种群的潜在影响，对于扬子鳄野生种群的保护至关重要。本项目的主要研究内容包括：自然孵化条件下扬子鳄的幼鳄性比、孵化温度和幼鳄性比之间的关系；扬子鳄雌雄幼鳄性别决定的温度敏感时期；巢址选择对扬子鳄幼鳄性比的影响及其主要的影响因子；气候变化对巢内温度以及野生扬子鳄幼鳄性比的影响。结果表明扬子鳄自然孵化的幼鳄性比会受到巢内孵化温度影响，不符合5:1的雌雄比假设；孵化温度与幼鳄性比之间有显著的相关性，即孵化温度越高，后代雄性比例越高；扬子鳄性别决定的温度敏感期发生在幼鳄胚胎发育的22-26期，即孵化的第34-48天之间，持续时间约为15天；坡向、植被盖度、干扰度这三个生态因子对野生扬子鳄的巢址选择有显著影响，而植被盖度和巢址距离水面的高度是影响扬子鳄巢内温度的主要生态因子；气候变暖会引起野生扬子鳄巢内温度上升，并可能导致幼鳄性别发生偏离。研究意义在于：扬子鳄自然孵化的性比结果说明扬子鳄5:1的雌雄比可能是雌雄存活率不同所导致的性比偏离；梯度孵化实验的结果进一步证明了扬子鳄属于FM的温度决定性别型，即高温偏雄，低温偏雌，据此可以实现扬子鳄幼鳄性比的人工调控；野生扬子鳄巢址选择结果可以为扬子鳄人工巢址位置的选择提供指导；扬子鳄性别转换的温度敏感期结果为扬子鳄实施性别调控的开始时间提供了依据；气候变暖对巢内温度以及野生扬子鳄幼鳄性比的影响，提醒我们在野生扬子鳄的保护过程中，不能忽视气候变暖对野生扬子鳄种群性比的潜在影响。