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