DISSERTATION RESEARCH: Coevolution and co-divergence in a classical obligate mutualism between Joshua tree (Yucca brevifolia) and its pollinators (Tegeticula spp.)

协同进化是捕食者和猎物、寄主和寄生虫、植物和传粉者等两个物种之间相互的自然选择和进化变化的关系。生物学家长期以来一直认为，共同进化帮助创造了地球上许多生命的多样性，但这种联系的证据只是间接的。这个项目将直接测试约书亚树和它的传粉者蛾之间的共同进化导致这些密切互动的物种一起分化的假设。约书亚树由两种不同的丝兰蛾授粉，每种都出现在寄主植物范围的不同部分；由不同蛾种授粉的约书亚树本身在关键的花卉特征上有所不同。为了确定这些平行的差异是否源于共同进化，研究人员将利用乔舒亚树的唯一种群，在该种群中，两种树类型和两种传粉者物种混合在一起。研究人员将在这个地点使用遗传标记重建约书亚树之间的家庭关系，这种方法非常类似于人类的亲子鉴定。然后，他们将使用这些重建的关系来估计约书亚树的特征可遗传的程度，即一棵树与其父母有多相似。如果与丝兰蛾相互作用的约书亚树性状显示出两种树类型之间的遗传差异比与交互作用无关的特征更大，那么约书亚树及其传粉者之间的共同进化很可能是造成这些差异的原因。该项目将涉及四名本科生志愿者助理，包括代表不足的群体。数据将与莫哈韦国家保护区(MNP)和约书亚树国家公园(JTNP)的科学工作人员共享，这两个国家总共包含了大多数受保护的约书亚树种群。关于约书亚树与其传粉者的相互作用以及约书亚树种群的遗传多样性和结构的信息对于保护这一旗舰物种至关重要，该旗舰物种正受到人类活动范围碎片化和全球气候变化的日益威胁。结果还将作为JTNP协会沙漠研究所系列讲座的一部分向公众公布。

Coevolution is a relationship of reciprocal natural selection and evolutionary change between two species, such as predator and prey, host and parasite, or plant and pollinator. Biologists have long believed that coevolution has helped create much of the diversity of life on Earth, but the evidence for such a connection is only indirect. This project will directly test the hypothesis that coevolution between Joshua tree and its pollinator moths has caused these tightly interacting species to diverge together. Joshua trees are pollinated by two different species of yucca moths, each occurring in a separate part of the host plant's range; and Joshua trees pollinated by different moth species themselves differ in key floral traits. To determine whether these parallel differences are due to coevolution, the investigators will make use of the only population of Joshua trees in which both tree types and both pollinator species are commingled. The investigators will use genetic markers to reconstruct family relationships between Joshua trees at this site, an approach very similar to paternity testing in humans. They will then use these reconstructed relationships to estimate the degree to which Joshua tree traits are heritable, that is, how much a tree resembles its parents. If Joshua tree traits involved in the interaction with yucca moths show greater heritable differences between the two tree types than traits unconnected to the interaction, then it is likely that coevolution between Joshua tree and its pollinators is responsible for those differences.The project will involve four undergraduate volunteer assistants, including underrepresented groups. Data will be shared with scientific staff at Mojave National Preserve (MNP) and Joshua Tree National Park (JTNP), which together contain the majority of protected Joshua tree populations. Information concerning Joshua tree's interactions with its pollinators and the genetic diversity and structure of Joshua tree populations are critical for conservation of this flagship species, which is under increasing threat from anthropogenic range fragmentation and global climate change. Results will also be presented to the public as part of the JTNP Association's Desert Research Institute lecture series.