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An uncommon “common garden”

A Joshua tree seedling in one of the gardens.

Spring in the desert means it’s time to plant Joshua trees. Over the past two weeks, Joshua Tree Genome Project collaborators and US Geological Survey staff led by Lesley DeFalco planted thousands of Joshua tree seedlings in gardens spaced across the Mojave Desert. The seedlings were started in greenhouse conditions last year, from seeds collected in Joshua tree populations growing in different climates across the desert. Seedling Joshua trees are delicate, and we start them gently — first the greenhouse, then planting with tilled soil and generous watering, then months of monitoring and more water, to let them put down roots.

But eventually we’ll step back and let the seedlings face the full stress of the different parts of the Mojave where the gardens are planted. It seems mean, but it’s a gold-standard experimental method to understand a key question that will help us protect the species as climate change ratchets up the heat and drought stress across the desert.

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Gathering the seeds of new science

Gathering the seeds of new science
An unopened Joshua tree fruit with seeds behind it. Some aren’t in this nice of a condition. Predation by the moth larvae and other grubs is common (Olivia Turner)

As the Joshua Tree Genome Project kicks off its NSF-funded study of climate adaptation in our favorite spiky desert plants, we’re posting updates on the progress of our work. Today we have a blog post from Olivia Turner, one of four interns with the Chicago Botanic Garden who’re working with JTGP collaborators Lesley DeFalco and Todd Esque to plant thousands of Joshua tree seedlings in experimental common gardens. This post was originally published on the website of the CBG’s internship program.

Hi all! This is Olivia. I am part of a 4 person intern team here on the Mojave Desert, NV working with the USGS on the Joshua Tree Genome Project.

This project is in collaboration with a handful of academic partners from all over the States and our mentors here in Nevada are among the Principle Investigators because they were some of the first scientists to ever investigate the life cycle, reproduction, demography, and the effects of climate change on Joshua trees!

So, why the JTGP?

Joshua trees are an icon of the Mojave, provide food for a large range of desert organisms, and have an incredible relationship with their obligate moth pollinators. Both organisms have a long co-evolutionary history together which is known to result in Joshua tree population differentiation. Given the changes in climate that are projected for the Mojave and surrounding areas, the JT is now also going to be facing selection based on abiotic factors.

Therefore, the Joshua Tree Genome Project was created with the goal of examining the Joshua tree’s local adaptation to climate, with the purpose of exploring the primary source of selection across populations (climate [abiotic] vs. pollinator driven population differentiation [biotic]). This will be done by identify ecophysiological traits that determine seedling tolerance to climate change and the genes that structure these traits (Project Proposal, 2020). Crazy cool! It is a multi-year study and we have the good fortune of being here right at the start. Oh, and of course, this project also involves sequencing, for the first time, the Joshua tree genome.

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