All living things must manage stress from their environment and interactions with other living things. Biologists have long believed that interactions with predators, competitors, and helpful mutualists are a powerful force in the history of life, helping to spur the formation of new species. However, it is difficult to test whether interactions between living things have been more important than the effects of the physical environment like heat, freezing, or drought. This project makes that comparison by taking advantage of a unique interaction between species that live in the extreme environments of the Mojave Desert. Joshua trees, the spikey, twisted-looking trees found across the Mojave, cannot produce fruit without the help of yucca moths. Joshua tree flowers appear to be adapted to the moths, but the trees also experience extreme heat and drought, and it seems likely that these effects of the physical, nonliving environment also impact their survival. The Joshua Tree Genome Project will use genetic sequencing and experiments with Joshua tree seedlings to study how the trees cope with different climates in different parts of the desert. The project collaborators can then compare the effects of climate on Joshua tree populations to the effects of their interaction with yucca moths. The team will also engage volunteers and science teachers across the Mojave region to measure and monitor Joshua tree populations in their own backyards. By examining the Joshua tree's adaptation to climate in detail for the first time, this project will help to answer a longstanding question in the history of life on Earth ? whether interactions between living things or the physical environment have been more important ? and develop scientific tools and community partnerships that can help protect Joshua trees under changing future climates.
The Joshua Tree Genome Project is a collaboration of ecologists, geneticists, bioinformaticians, and plant physiologists at Willamette University, California State University Northridge, the Universities of Alabama and Hawaii, and the US Geological Survey Western Ecological Research Center. The collaborators will plant Joshua tree seedlings at common-garden sites around the Mojave, monitor their growth and physiological performance, and use RNA sequencing to identify genes that are differentially expressed in different climates. The team will complete a Joshua tree reference genome and use it with the gene expression results to design a sequence capture array for targeted sequencing of hundreds of trees. Targeted sequencing will allow them to perform genome-wide association study (GWAS) of physiological traits that contribute to seedlings? survival and performance in the common gardens, and of floral traits related to pollination by yucca moths. The team will then use landscape genomic analyses to identify genes showing signatures of local adaptation to variation in climate and moth traits. Meanwhile, the team will expand a participatory science program working with Mojave-regional conservation nonprofits and K-12 educators to train volunteers to survey the demography of Joshua tree populations, recording how many trees flower and produce fruit, and how many young trees are present to renew the population. Finally, the team will use the results of their genetic analyses to build a genomic prediction protocol that can project the physiological and pollination-related traits of a Joshua tree population from genetic data alone. The team will use this protocol to predict the traits of trees at sites profiled by volunteer surveys, and test for relationships between populations? predicted trait values and their demographic health. This will allow them to identify specific traits that influence the fitness of Joshua trees in current conditions, and would provide a tool to assess the resilience of Joshua tree populations in future climates.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
