A mania for jumping bristletails

Got a package a couple of days ago from Kauai. Not coffee or a sea turtle t-shirt or any of the other usual Hawaiian items, but something far more exciting—a small glass vial containing seven jumping bristletails preserved in ethanol! So, of course, I spent most of the rest of the day peering through a dissecting scope, trying to identify the things.

My friends/colleagues John Gatesy and Cheryl Hayashi and I have been studying these flightless insects for a number of years and can spout off various reasons why they’re fascinating from a “serious” scientific standpoint. But I just want to use these new Kauai specimens as an excuse to post a bunch of photos and give some sense of the attraction of these creatures for a geeky naturalist and taxonomist.

 

Mesomachilis nearctica in the Egan Range, Nevada.

Bristletails are extremely anatomically conservative—every bristletail pretty much looks like a bristletail. In a weird way, that’s part of their appeal; the diversity within the group is all about subtlety, not extravagant differences. And am I crazy or does this insect look kind of edible, like a tiny land shrimp?

 

Cheryl on Mt Moriah in the Northern Snake Range, Nevada.

The pale, carbonate rocks on Mt. Moriah might be 500 million years old, making them older, but not vastly older, than the bristletail lineage, which probably split 400 million years ago or so from the evolutionary branch that would become all other insects. Bristletails we collected here turned out to be a new, yet very abundant and widespread species.

 

Me, collecting on the Dana Plateau in the Sierra Nevada, just outside of Yosemite National Park. Photo by Seung-Chul Kim.

As John said on a recent collecting trip to Big Sur, bristletails seem to be found in really nice places (although one of the biggest concentrations of them I’ve ever seen was on an outhouse).

 

An especially handsome bristletail face—Petridiobius arcticus from Bellingham, Washington. Photo by Merrill Peterson.

Like other bristletails, this one looks like it’s wearing goggles and a gas mask. The elongate reddish brown blobs under the compound eyes are another pair of eyes, called lateral ocelli. Their shape is a key taxonomic character; looking at bristletails under a microscope, the first things I check out are the ocelli.

 

Neomachilis halophila from near Cambria, California.

When this bristletail was feeding, its compound eyes completely disappeared under the segment just behind them. (Compare the two photos. The white things are the lateral ocelli.) When I saw this, I got very excited and wrote to a couple of entomologist friends…and found out, to my slight disappointment, that having part of the head disappear like this happens in many kinds of insects. So it’s not unique, but it’s still kind of cool.

 

Neomachilis perkinsi from Kauai. Photo by Merrill Peterson.

At some point we learned that there are a few native bristletail species on the Hawaiian Islands and that they probably came from North America (which is weird—most Hawaiian arthropods, especially ones that don’t fly or drift on the air, came from other Pacific islands or from Asia). That led to several trips to Hawaii to collect specimens and verify the biogeographic story, still a work in progress at this point. The paired structures that are curved down sort of like fish hooks are the maxillary palps, which are used by the male to tap or grasp the female during mating, and are extremely thick in male perkinsi. This is the kind of thing that gets a bristletail taxonomist going.

 

One of the new specimens from Kauai.

This is a male, but it doesn’t have the thick maxillary palps, and, therefore, isn’t perkinsi. It’s probably Neomachilis insularis, a species never before identified from Kauai. Apart from the fact that these specimens may be a key for our biogeographic work, it’s just satisfying to be able to identify a species from a place where it’s never been found before.

 

John, on the island of Molokai, looking like he might try to flap himself airborne. The wings are actually “beat-sheets” used to collect arthropods.

Neomachilis halophila on driftwood on the Oregon coast. Is this how they got to Hawaii?

My kids on that same Oregon beach, presumably not thinking about taxonomy, long-distance dispersal, or the deep history of life on Earth.

Our son Eiji thinks bristletails are cool. But our daughter Hana keeps it real—“bristletails are dumb,” she says. (I think the subtext there is “When dad’s looking at those things under the microscope, he won’t play with me.”)

The surprises go both ways: flycatchers trapped in the Americas

A lot of animals that you’d never think would be able to cross oceans on their own have apparently done exactly that—for instance, monkeys and burrowing lizards almost certainly crossed the Atlantic, and iguanas probably crossed the Pacific. However, there are also animals that seem well-equipped to make such transoceanic colonizations, but don’t seem to have done it. I’m thinking especially of many kinds of birds.

Tropical forest birds are somewhat notorious for their lack of gumption when it comes to crossing water. For many of these species, narrow sea straits and large rivers are major barriers to movement, despite the fact that it might only take a few minutes for a bird to fly over them. I’ve just been looking at maps in a guide to the birds of Venezuela, and one thing that immediately jumps out is that many species are only found on one side of the Orinoco or the other. They’re certainly capable of flying across, but they don’t seem to do it, or at least not often enough to become established on the opposite side.

On a wider scale, there are some large taxonomic groups of birds that are entirely or almost entirely confined to contiguous landmasses, only being found in the Americas or only in Australia, for instance. A striking case is the group called the Tyrannides (the New World suboscines excluding the Sapayoa), which includes the New World flycatchers, antbirds, woodcreepers, cotingas, and manakins, among others. This group apparently evolved from a common ancestor that lived in South America some 50 million years ago, and today includes close to a thousand species. The suboscines are a huge part of the bird fauna of Central and South America, and many breed in temperate North America and migrate to the tropics or subtropics for the winter.

A few species in this group have colonized the Galápagos, about 600 miles west of South America, but none have become established on more distant Pacific islands. And, perhaps most surprising, none have colonized Africa or Europe. So, here’s a group that’s some 50 million years old, is very diverse, and is made up of birds that are strong fliers, many of them routinely migrating thousands of miles between breeding and wintering areas, but for some reason they haven’t managed any really long colonizations over expanses of ocean.

Vermilion Flycatcher in Colombia, part of an old and very diverse group that can’t seem to get out of the Americas. Photo by Julian Londono via Wikimedia Commons.

I imagine some people will take this example as a reason to doubt the whole modern approach to biogeography or even the theory of evolution. They might say that the conclusion that monkeys made a colonizing voyage across the Atlantic, but a large group of strong-flying birds hasn’t managed it just shows the absurdity of the whole Darwinian worldview. (That debate is something I’ll probably have to take up in a future post.)

Obviously, that’s not what I believe. Instead, I think our views about how easy/difficult it is for various organisms to make long ocean journeys and establish themselves in new lands are often too simplistic. In the case of birds, we tend to focus on the fact that they can fly, and imagine that this trumps everything. For the New World suboscines, though, there are presumably other factors that have held them back, keeping them a “provincial” American group. It may be relevant that some North American landbirds occasionally wind up in the Hawaiian Islands as what birdwatchers call “accidentals,” but, as far as I know, there are no such records in Hawaii for flycatchers or other New World suboscines. There’s probably a reason for that—maybe someone out there knows why—and it could help explain why this group has remained “stuck” in the Americas.

In my book I talked about scenarios for how the unexpected happened, like how bristletail insects might have made it from California to Hawaii as eggs stuck to driftwood or how crocodiles might have “surfed” on ocean currents across the Atlantic. The New World suboscine birds suggest there’s a lot of room for discussion of the inverse too, that is, why the expected often hasn’t happened.