Note: This story is intended to be listened to. Text associated below is simply a transcript of the audio but does include some great visuals.
“My name is Kathryn Busby and I’m a wildlife biologist with the United States Geological Survey. My background is mainly in native bees, but also mutualist species interactions.”
A mutualist relationship brings benefits to all the species involved. Think bees and flowering plants.
Busby and I are sitting under a bunch of blooming orange trees. We can’t see them, but the bees are definitely buzzing above us. The air smells fragrant, sweet. We’re not here to talk bees, though.
“I came from a background in insects and species interactions. And then I found my way into this lab, where they said, we have an opening for a wildlife biologist, if you’d like to be called that while you do this insect work and continue doing the research that you do. So that’s how I ended up in my current position.”
Her USGS job took her to western Arizona, which is part of the Joshua tree’s range; it extends through parts of California, Arizona, Utah, Nevada and northwestern Mexico.
Joshua trees can live for hundreds of years. Some have been known to live for up to a thousand years. They can be up to 30 feet tall. Yet they grow very slowly; for the first decade of a Joshua tree’s life, they rise about three inches a year. Joshua trees wouldn’t exist at all, though, if it wasn’t for a very elusive tiny bug.
“So they spent much of the year underground as larvae, and they look like a grain of sand or a little ball of sand. So, it’s very difficult to detect them. And because of that, it’s difficult to assess their population status.”
Yucca moths are what’s known as a specialist species: One of the main things they do is pollinate the Joshua trees. To give you an idea, this is the sound that wax moths make. They’re slightly bigger, about half an inch long.
Without the Joshua trees, the yucca moths wouldn’t have a host plant. And without the yucca moths, the Joshua trees wouldn’t be able to produce seeds.
Theirs is what’s known as obligate mutualism: They’re both dependent on each other for survival. So what scientists are trying to figure out is how their relationship will keep evolving over time, especially in the face of climate change.
“It’s a developing area of research. And there’s going back, maybe 130 years or so, there have been some descriptors of this system.”
It’s true: The yucca-yucca moth pollination system was first described in 1873. In a letter to his close friend, British botanist Joseph Dalton Hooker, Charles Darwin described yucca moth pollination as — quote — “the most wonderful case of fertilisation ever published.”
Only in the past three decades have scientists focused again on the yucca moth-Joshua tree relationship — largely because climate change is putting both species at risk.“There’s no corner of the globe that is still pristine wilderness or hasn’t been impacted by humans in some way, and I think we humans get very human-centric and are thinking sometimes we need a reason why to, you know, prevent the species from going extinct. Is it good for our food? Is it good for our medicine?”
One could argue that they have no real use to us humans. They just are — just one of many models of species working together, evolving together, being tied at the hip against the odds.
But they do have a use: They’re part of a unique Mojave Desert landscape that has existed for millions of years. And for Busby, saving all of them feels especially urgent.
“I’ve been motivated in my research personally because I want to know what happens if we if we do crank up the temperature and dry things out in the desert. What will happen? And are there ways to mitigate that?”
Will they continue to weather change together, over time?
Note: This story was updated to note that one of the main things yucca moths do is pollinate Joshua trees; to reflect a distinction between Joshua trees flowering and their seeds; and to clarify that co-evolution won’t likely save both species.
Original audio by Ruxandra Guidi, with sound effects from BBC Sound Effects.
Ruxandra Guidi is a correspondent for High Country News. She writes from Tucson, Arizona. Follow her on LinkedIn.
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