How have animal genitalia co-diversified between the sexes? Linking biomechanics to genital evolution in insects

生殖器的快速分化是内分泌失调的普遍趋势。在过去的几十年里，进化过程受到了越来越多的关注。大量的经验和理论研究表明，性选择是生殖器多样化的主要驱动力。然而，以前很大程度上被忽视的假设，锁和钥匙，自然选择，和多效性，最近被重新审视。在生殖器多样化的驱动力发挥重要作用的问题仍然积极讨论。尽管过多的生殖器多样化的研究，不同的生殖器结构和它们的功能之间的联系很少被研究。重要的是，选择力不直接作用于形态特征，而是通过功能。因此，我和我的合作伙伴一直在研究昆虫雄性和雌性生殖器相互作用的生物力学，发现它们的数量形状变化可以在很大程度上改变功能。在之前的一个项目中，我们提出了一个功能景观（FL）假设，该假设指出，在密切相关物种中观察到的数量变异中，存在假设的功能较低的雄性和雌性生殖器组合，这可能是生殖器共同多样化的内在机制在上述可变驱动力下。该项目的最终目标是检验这一FL假设。为了实现这一目标，我们将实现以下目标，重点是在昆虫的细长生殖器和精子储存的渗透过程中的雄性和雌性性状之间的相互作用。(i)我们将发现雄性/雌性性状特性和功能之间的因果关系;这些因果关系将使用不同的昆虫群体和应用生物力学方法进行探索。我们将通过现代显微镜技术、物质分布分析和理论计算的结合，找到男女性相互作用的机械原因。(ii)我们将测试FL假设;特别是，我们不仅将生殖器的实际数量变化联系起来，还将通过人工模型进行机械测试，将假设（自然界中不存在）的变化与潜在功能联系起来，例如，具有不同形状和材料的3D打印男性和女性生殖器将用于模拟具有不同结构和材料特性的渗透过程。因此，我们将能够比较现实的生殖器和假设的功能，以测试FL假设。此外，还将发表一篇关于外语假设的观点和评论文章，以讨论这一假设的有效性。该项目将提供一个关于生殖器多样化的补充和迄今为止缺失的视角，并首次进行具体研究，以检验该理论的普遍性。

The rapid divergence of genitalia is a prevailing trend among internal inseminators. The evolutionary processes have received burgeoning attention over the past few decades. Considerable empirical and theoretical research suggests that sexual selection is a major driving force of genital diversification. However, previously largely neglected hypotheses, lock and key, natural selection, and pleiotropy, have recently been revisited. The question of which driving forces play a significant role in genital diversification remains actively discussed.Despite the plethora of previous research on genital diversification, the linkage between diverse genital structures and their functionality has rarely been studied. Importantly, selection forces do not act directly on morphological characteristics but rather via functionality. Therefore, my collaboration partners and I have been examining the biomechanics of male and female genital interactions in insects and found that their quantitative shape variations can largely alter functionality. In a previous project, we developed a functionality landscape (FL) hypothesis that states that among quantitative variations seen in closely related species, there are hypothetical male and female genital combinations with lower functionality, which could be an intrinsic mechanism for the co-diversification of genitalia under the abovementioned variable driving forces.The ultimate goal of this project is to test this FL hypothesis. To accomplish this goal, we will achieve the following objectives by focusing on the interaction between male and female traits during the penetration of elongated genitalia and sperm storage in insects. (i) We will find causations between male/female trait properties and functionality; these causations will be explored using diverse insect groups and applying biomechanical approaches. We will find the mechanical causations of male and female sexual interactions by means of combinations of modern microscopy techniques, material distribution analyses and theoretical calculations. (ii) We will test the FL hypothesis; in particular, we will link not only realistic quantitative variations of genitalia but also hypothetical (absent in nature) ones with potential functionalities by conducting mechanical tests with artificial models, e.g., 3D-printed male and female genitalia with variable shapes and materials will be used to simulate the penetration process with different structural and material properties. Consequently, we will be able to compare the functionalities between realistic genitalia and hypothetical ones to test the FL hypothesis. Furthermore, a perspective and a review paper on the FL hypothesis will be published to discuss the validity of this hypothesis. This project will provide an additional and hitherto missing perspective on genital diversification and the first concrete studies testing the universality of the theory.