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I trapped lizards in Los Angeles because their DNA holds secrets

How do lizards cross the road? Their DNA suggests they don't

To handle a baby lizard, you gently pinch its shoulders. This pushes its front arms against its body. If you grip farther back, the lizard wiggles more, and may struggle free. This is what I’m learning a little after 7AM on a Thursday morning in Thousand Oaks, California, just north of Los Angeles. We have already parked in a suburb and climbed onto land protected by the Santa Monica Mountains National Recreation Area. I can still see the cul-de-sac from the pitfall traps, where we are gathering lizards. It is early August: baby lizard season. These babies are, quite literally, a glimpse of what the future of the ecosystem looks like — which is why we’re taking their DNA.

A pitfall trap, by the way, looks like a very large T, or sometimes like a Y that got a little lazy. The letter is formed by fencing that’s half a meter (slightly more than a foot and a half) tall, which drives lizards to go around the obstacle. Along the fence — and at the ends — are white five-gallon buckets, which are embedded in the ground, with lids propped open by wood slabs. Katy Delaney, a wildlife ecologist at the National Park Service, and her intern, Rachael Pahl, are going from trap to trap. "Instead of going over the fence, they go right or left," Delaney tells me. "And then they fall in a bucket." Pitfall traps don’t just catch lizards, though, they’re more like Christmas presents that, once unwrapped, could give you a whole variety of creepy-crawlies. During my time with the researchers, we get a night snake, two live shrews (and one dead one), two live mice (and one dead one, which was being eaten by another mouse in the trap with it), two scorpions, plus a few crickets, a lot of ants, and a wolf spider. (According to Delaney, other highlights include baby rabbits and mockingbirds. The traps also contain sponges, in case of amphibians, but salamanders in particular have an irritating habit of scaling the fence, and will sometimes simply watch the ecologists check the traps.)

The National Park System is turning 100, and The Verge is celebrating with Wilderness Week: a look at the natural world, its freaky critters, and its future.

I’m here for lizards, though. Though I tend to prefer much larger animals, I find these little critters oddly charming; their expressions register to me as deeply skeptical. Fair enough, I guess; I suppose it’s not often they’re picked up by large predators that, instead of eating them, simply want to characterize them. After the lizards are removed from the trap, they’re put in a plastic Ziploc bag and weighed. The smallest baby lizards register at 2.5 grams, which is just the weight of the bag they’re in. So the researchers round their weight up to half a gram, which means the smallest baby lizards weigh less than a sixth of a teaspoon of salt. Next, the researchers pluck the lizards from the bag and try to stretch them against a ruler to measure them; this usually involves flipping them upside down. While lizards are very well camouflaged — it’s hard to see them against the desert background — their bellies are often surprisingly beautiful. (The Western fence lizard, for instance, has bright blue patches along its tummy; one side-blotch lizard the team caught had bright-orange mites in its armpits.) DNA samples are taken and labeled. Then the lizards are released.

The pitfall traps and DNA samples are part of a long-running study, one that’s been going since 2000; it’s one tiny part of the National Parks Service’s Inventory and Monitoring Program, which is meant to collect and analyze data on the animals in the parks. These data help guide decisions about conservation, and apparently the whole thing seems to involve a lot of paperwork and protocol, in addition to lizards. This site, and the next nine I’ll visit that day, are places where biologists have been tracking animals. There’s a high-level purpose: this kind of long-term monitoring lets scientists know how animals coping with the changes humans have wreaked on the landscape — and the longer a dataset you have, the better you can track those changes. In practice, a lot of the work is both difficult and mundane. There are the details of what you caught: how many fence lizards, side-blotch lizards, skinks. How many, what kind, where. It’s a labor-intensive project, which requires off-trail hiking in the desert. That’s why we’re out so early; we want to beat the heat, and make sure any lizards caught in the traps do, too. Beating the heat is kind of a futile quest; I’m sweating profusely by 9AM.


The Santa Monica Mountains National Recreation Area is a remarkable place for many reasons, not least of which is that it contains the entirety of Malibu. The mountains are almost totally isolated from any other wild land — they’re surrounded by agriculture and LA suburbs. Even within the park, there’s significant encroachment by people (for instance: Malibu). By 2050, almost half the area — 47 percent — may be urbanized, one study has projected; only 11 percent counted as urbanized in 2000.

What the park is struggling with now is something that will become increasingly common around the world as the human population continues to expand: the wilderness areas will be cut off from each other. That’s bad news for the animals in more ways than one. Not only does it mean less land, it also means more "conservation islands" — wilderness areas that don’t connect to anything else. This means animals are often cut off from unrelated animals — and results in inbreeding.

The wilderness areas around Los Angeles aren’t the only place where this is happening. In South Africa, for example, cheetahs are laboriously tranquilized, tagged, and DNA tested before being shuttled between parks. Cheetahs need a lot of space to run and hunt, and they can’t easily move from park to park — thanks to the fences designed to protect them from poachers. Closer to home, the bobcats around Los Angeles are struggling with being cut off from others of their own species, driving inbreeding; so too are Los Angeles’ mountain lions. In some places, the pressures on local animals are too much and they vanish entirely.

There’s a reason for that. Inbreeding decreases genetic diversity, which means that deleterious mutations can pile up. That means a greater likelihood of a population crash, says Brad Shaffer, a biologist at the University of California Los Angeles. This is especially true in rapidly changing environments, where genetic variation can make it easier to adjust. And most environments are rapidly changing, now, thanks to climate change. The effects are obvious for the big, charismatic cats — but they aren’t the only ones who are feeling the squeeze. A paper Delaney published with other researchers in the journal PLOS One in 2010 shows that lizards in different areas are beginning to accumulate different mutations. When two groups of the same species are separated and interbreed for long enough, they diverge into other species. The classic example is a group of 14 species of Darwin’s finches in the Galapagos islands; though they share a single species as their common ancestor, they evolved separately on different islands.

In the Los Angeles area, it is helpful to think of the areas split by highways as islands. In Delaney’s paper, what matters most for the genetics of skinks, Western fence lizards, and side blotch lizards isn’t how far apart the wilderness areas are, it’s whether they’re split off from other areas by highways and roads. The largest genetic drift appeared in places where the oldest highways had been built — right around Thousand Oaks.

That study used data from 2000 to 2005, but the traps are still running. In fact, that’s what we’re doing this morning with the pitfall traps; bringing back more information on the lizards, as well as genetic samples taken from their nails and the tips of their tails. The study has been running for 16 years now, and it may provide a valuable window into the effects of habitat fragmentation that could help guide conservation policy. That’s 16 years of someone — a staffer or an intern — getting up bright and early to check traps daily for a week. The next week, a new set of traps is on deck. There are a total of 80 of these traps, and they're checked every other month.


Lizards only live a year or two, so they’ve gone through many generations in the years they’ve been separated by highways. It’s not yet clear whether the data collected is simply showing that the individuals aren’t moving back and forth, or whether it’s strongly important selection. If there were very different environments on either side of the road, the lizards might start to specialize. If, for instance, it’s wet on one side and dry on the other, UCLA’s Shaffer says, that might be enough to get specialization, provided the populations of lizards on either side aren’t too small. But most of the habitats aren’t very different on one side of the road than on the other.

Unlike the big cats, most of these lizards aren’t endangered species. The Western fence lizard, for instance, is classed as having a stable population on the IUCN red list of threatened species and it’s classed as "demonstrably widespread, abundant and secure" on the Natural Heritage Programs and Conservation Data Centers list. That may be in part because these lizards aren’t at the top of the food chain; top predators like bobcats, cheetahs, and mountain lions require access to a lot of area and a lot of prey to survive. Lizards, on the other hand, typically eat insects and serve as a food source for birds, snakes, and shrews, and even hungry coyotes and big cats. They’re an important way to transfer energy in the ecosystem from bugs to big-bodied animals, a crucial food bridge. Knock them out of the system, and everything farther up the food chain suffers. Lizards are particularly crucial for dry areas, because they flourish there when other animals struggle.

While the lizards are unlikely to go extinct from California, they may vanish from specific plots of land. If something like a catastrophic forest fire roars through their area, the survivors can’t travel to an unaffected area and then return. Worse, if the lizards are wiped out entirely, new groups of lizards can’t come into the area and recolonize. These local extinctions can have big consequences for the local food chain.

local extinctions of lizards aren't just bad news for the food chain — there may be human consequences

Local extinctions are possibly bad for people as well, says Sean Anderson, an ecologist at California State University Channel Islands. A 1998 study led by Robert Lane of UC Berkeley showed that Western fence lizards are also a Lyme disease preventive task force. Ticks harboring the bacteria that causes Lyme disease are purged of the bacteria when they feed on these lizards — which means that any tick that then goes on to bite a human won’t spread Lyme disease. It may be part of the reason why rates of Lyme disease infection are lower in the Western US than back East. Of course, ecology is rarely simple; remove the lizards and the tick population drops as well — though they switch their preferred host to female woodrats, which don’t have any Lyme-preventive properties. It’s hard to know what the future holds for California’s lizards, because fragmentation has unexpected effects. For instance, the Western fence lizard, one of the most common species found in California, has almost totally vanished from Los Angeles proper. (The third most common lizard in the state, the alligator lizard, has had an easier time and is found in plenty of Angelenos’ backyards.)

Something about how we’re managing our landscapes means that the two most common species of lizard in the west are wholly absent from most of the city, and it’s not clear what, UCLA’s Shaffer says. It could be our yards, our pets, our fertilizers — really, anything. "We manage landscapes in ways, very unintentionally, that are good for some species and horrible for others," he says. "The data Katy’s collecting in the mountains allows us to use genetics to at least try to understand how we’re managing landscapes in ways that help some species and don’t help others."


There probably isn’t a quick fix for fragmentation. While wildlife crossings — like ones underway in Montana and another one planned for the Los Angeles area at Liberty Canyon — are a definite help to large-bodied creatures, it’s not clear how effective they are for smaller ones, like lizards, says Anderson. There are already culverts and creeks that go under roadbeds that lizards could take advantage of, but they often don’t. They may be picky about how they move and when, Anderson says. (For instance, some species of salamanders will only move on moonless nights, when it’s raining a little — and if the conditions aren’t perfect, they just won’t go.) Of course, humans could get more hands-on, as we do with cheetahs, by physically moving lizards across roads — but that’s expensive and possibly dangerous for the humans, who are also at risk of being hit by cars.

Perhaps the better solution is to think about the lizards at a local level, says Shaffer. Part of that is understanding what’s making the lizards disappear from developed areas, and trying to create spaces that will allow them to coexist. "One of the real aesthetic and ecological pleasures of living in Southern California is you have wildlife around, you have ecosystems in your yard," he says. "To my mind, that’s at least as important and compelling a reason to understand these dynamics and think about ways to keep those lizards in those backyards, keep them on school grounds and places where people see them and learn from them and are aware of them and think they’re cool."

Because the lizards are cool, and they’re worthy of keeping around for their own sake, not just because of the role they play in the ecosystem. At one of the traps, as Rachael reaches in to remove a whiptail lizard, it runs up her arm and away. She’s dismayed — no genetic data, no weight, and no measurement — but I’m tickled.

It’s part of what I like about wild animals; their cunning, their unpredictability, and their adaptiveness. For the right lizard in the right trap, a human arm reaching in is simply an exit strategy. You could say lizards punch above their (very slight) weight in their capacity to delight us. They have their own strategies, their own aims, their own quirks; it’s a welcome reminder, near a human-centric cityscape, that the world isn’t just about us. For me, at least, this is reassuring. Whether or not I hit my deadline or scoop another publication, the lizards will go about their lizard business — unmoved, with their permanently skeptical expressions.

The point of a national recreation area is to put nature near people, to provide us with access to these creatures, so that we can be surprised, and maybe even delighted. You don’t have to be a hardcore wilderness freak to drive just north of the Valley and go for a hike. This is the nature that’s most accessible, that’s easiest to see. And as long as we’re trying to think about our impact on the animals we live near, the National Park Service will be out hiking off-trail, picking up lizards, trying to do genetic analyses, and telling us about our wild neighbors. Well, if we want to live with animals — and I personally think it’s really valuable to do so — it’ll certainly take work.