Collaborative Research: Developing novel methods for estimating coevolutionary processes using tapeworms and their shark and ray hosts

寄生虫无处不在，许多物种与它们的宿主一起经历了很长的进化时间，并且对它们寄生的宿主种类非常挑剔。有些出乎意料的是，最近的研究表明，许多寄生虫物种不一定与其宿主具有相似的进化历史；相反，其他因素可能在形成这些寄生关联中起作用。然而，对于哪些其他因素，如饮食或地理分布，影响了这些关系，人们知之甚少。这主要是因为目前还没有一种评估其他因素重要性的方法。这项研究将开发一种方法，并将使用由鲨鱼和黄貂鱼的绦虫组成的一个著名的物种丰富的系统进行测试。这种方法将广泛适用于其他共同进化系统，不仅有助于我们进一步了解宿主-寄生虫系统，而且还有助于我们了解其他涉及密切关联的生物系统。密切的物种关联无处不在，更好地了解环境在形成物种关联中的作用，对于预测生物多样性对气候变化的反应至关重要。该研究将培养进化生物学定量技术方面的博士后研究人员和研究生。这个项目朝着一个更机械的生物影响模型的方向发展，涉及寄生虫和宿主之间的共同进化。将生成大量的寄生虫属的系统发育，将生成相应的鲨鱼和鳐（elasmobranch）宿主的经过时间校准的系统发育，并将编制可靠的寄生虫-宿主关联数据。将开发使用近似贝叶斯计算的新方法和开源软件工具，以允许估计和测试寄生虫-宿主系统进化的模型。寄生虫进化的模型将在地理上明确，并将包括诸如共种、环境驱动的灭绝、传播和宿主转换的地理限制以及中间宿主的一些影响等因素。这些丰富的经验数据集将允许使用稳健的交叉验证方法进行假设检验。最终的结果将是一个方法学框架，用于评估多种因素的贡献，除了共同发育，在结构宿主关联和寄生虫进化。新的软件将用于解决三个主要的研究问题，这些问题是关于寄生虫-宿主相互作用的基础因素，包括各种因素在不同性质的系统中所起的相对作用。

Parasites are everywhere and many species have been with their hosts for a long evolutionary time and are extremely particular about the kinds of hosts they parasitize. Somewhat unexpectedly, recent research suggests that many parasite species do not necessarily share a similar evolutionary history with their hosts; rather other factors may be at play in shaping these parasitic associations. Yet, little is understood about which other factors, such as diet or geographic distribution, influence these relationships. This is largely because a method for assessing the importance of other factors is not currently available. This research will develop a method and will test it using a well-known and species-rich system consisted of the tapeworms of sharks and stingrays. This method will be widely applicable to other coevolutionary systems, helping to further our understanding not only of host-parasite systems in general, but also of other biological systems involving intimate associations. Close species associations are ubiquitous and better knowledge on the role of the environment in shaping species associations will be critical to forecasting biodiversity's response to climate change. The research will train postdoctoral researchers and graduate students in quantitative techniques in evolutionary biology.This project moves towards a more mechanistic modeling of the biological influences involved in the coevolution between parasites and hosts. Phylogenies will be generated for a large number of cestode genera, time-calibrated phylogenies will be generated for their corresponding shark and ray (elasmobranch) hosts and robust parasite-host association data will be compiled. New methods and open-source software tools using approximate Bayesian computation will be developed to allow the estimation and testing of models for the evolution of parasite-host systems. The models for parasite evolution will be geographically explicit and will include factors such as cospeciation, environmentally driven extinction, geographic constraints on dispersal and host-switching, and some effects of intermediate hosts. These rich empirical data sets will allow the use of robust, cross-validation methods for hypothesis testing. The end result will be a methodological framework for assessing the contributions of multiple factors, in addition to cophylogeny, in structuring host associations and parasite evolution. The new software will be used to address three main research questions regarding factors that underlie parasite-host interactions including the relative roles various factors play in systems with different properties.