“越大越好吗？"---从基于体型、声音和气味的配偶选择对性选择理论再验证

Sexual selection, through intra-male competition or female choice, is assumed a source of strong and sustained directional selection in the wild. It predicts that females prefer males with elaborated ornaments or extraordinary morphological traits. Those traits may honestly indicate that the bearers either are bigger in body size or have a better genetic quality. A wealthy of literature from broad taxa of species with significant secondary sexual traits has supported the prediction of “the bigger is the better”. For species of showing less or without secondary sexual traits, however, we know little about whether this prediction works or not. Moreover, some update evidences show that females of some species prefer to medium sized males to larger males in choosing mates during mating season. This contradicted the prediction of the bigger the better drawn from sexual selection theory. The giant panda shows little sexual secondary traits, and its body size experienced a change from small to large and then medium in the evolutionary history. Yet we know nothing about whether female pandas still keep the preference to larger male in choosing mates, and are there any other traits/signals by which females used to evaluate the males’ quality in addition to the body size. To answer those questions, we hypothesized that female pandas still show preferences to larger males by following the sexual selection theory, and they may use other sources of traits/signals to assess male quality as well. To test those hypotheses, we first use the captive pandas to investigate females’ preferences to males in larger or smaller size in mating season, and to examine if the body size change fits to Weber’s law. Next, we use playback technique to test if females prefer to bleating, one of the two major vocalizations between male and female during courtship in mating season, from larger male against those from smaller males. Thirdly, we will simultaneously present two anogenital secretions odors/urine odors from larger and smaller males, respectively, to females in the mating season, to test if they prefer odors from larger males to those from smaller males, i.e. if the bigger is the better. Last, we selectively use vocalization recordings of bleating from wild pandas, and repeat the playback experiment in wild pandas to test the hypothesis. The results will not only provide a new insight on sexual selection in species with less or without secondary sexual traits, but also shed new light on the relationship between sexual selection and natural selection.

性选择作为一种定向选择，它预测雌性倾向选择具有夸张第二性征-即体型较大或遗传基础较好的雄性。针对性二型特征明显的类群所开展的大量研究已证明“体型越大越好”。然而，对性二型不明显/缺少的物种却缺乏了解。此外，最新研究显示，在部分种类的配偶选择中，雌性偏爱的雄性体型并非最大而是中等。这与性选择理论的预测相悖。性二型特征不明显的大熊猫，其体型在进化中曾发生由小到大再到小的变化。那么发情雌性是否依然保留对体型较大雄性的选择偏好？此外，它们是否凭借其他指标评估、选择雄性?本项目拟采用录音回放和气味暴露法，双向选择实验，分别对体型、咩叫声和气味三种信号进行实验，验证雌性对雄性的选择是否符合“体型越大越好”的预测，这些指标的变化是否符合Weber’s 法则。最后，选择野生个体，以咩叫声进行重复验证。研究结果将首次在性二型不明显的大型哺乳类验证“越大越好”的假说，揭示其配偶选择机制，补充并完善性选择理论。

有关性选择和配偶选择的问题一直是动物行为学和进化生物学探讨的一个热点问题。如何选择一个合适的配偶、提高适合度是大多数雌性面临的关键问题。Weber’s法则认为，雌性应该选择高质量的雄性个体作为配偶。然而评估雄性质量好坏的指标，即雌性配偶选择的机制依然是一个具有争议的问题。本研究以圈养雌性大熊猫为研究对象，采用双向选择实验方案，检验其是否基于雄性的尿液气味和叫声来区分并选择配偶，即是否雄性体型越大越好。结果发现：1）无论对气味还是叫声的测试结果，均不支持Weber’s 法则。2）雌性个体偏爱选择与自己亲缘关系较远，即与自身基因差异较大的雄性个体做配偶。这符合非选型交配假说。3）雌性对高和低配对适合度指数（MSI）的雄性并未表现显著选择偏好，表明国际大熊猫繁育委员会基于MSI提供的年度繁殖配对建议并不科学。4）对大熊猫化学通讯媒介物可能来源——不同竹子及同种竹子不同部位的挥发性化学成分的分析结果，发现不同的竹子种类和不同部位挥发性物质不同，这可能对其性外激素的组成和比例有潜在影响，进而影响其配偶选择。我们的研究结果为进一步探讨大熊猫的配偶选择及其机制提供了新的切入点，同时为圈养大熊猫繁育生产实践提供了重要借鉴，也为探讨其他哺乳动物的配偶选择及其机制创造了基础。. 因疫情管控原因，临时调整工作计划和内容并获得如下结果：1）对2013芦山地震前后3天圈养大熊猫行为比较分析，发现大熊猫并未对即将发生的地震表现特殊行为反应，即大熊猫不能预测地震的发生。2）针对1929-2021年有关大熊猫研究文献的计量学分析，结果发现，中国始终是针对该物种开展研究的主体，并存在广泛的国际合作。虽然大熊猫的保护级别被下调，大熊猫仍然是热点研究对象之一，而且可能会持续下去。近些年大熊猫的研究工作主要集中于气候变化、人类活动干扰和大熊猫国家公园建设等。3）以雌性个体的繁殖年龄为评估母本质量的间接指标，针对圈养大熊猫1935-2019年出生个体的性比数据，检验了Trivers-Willard 假说，结果不支持该假说。同时发现，母本生育年龄越大，其子代寿命越短。. 基于以往多年的研究基础并结合本项目的需求，申请并获得1项技术发明专利，2项计算机软件著作权专利。