Galápagos Week: World Within Itself

Last summer, after spending a week in the Galápagos, I wrote a six-part series for The Last Word on Nothing about what I had learned. I’m on vacation this week, so I figured it was a good time to re-publish the series for Phenomena readers. This is the third installment. You can read the first post, about tortoises and donkeys, here, and the second, about eerie mounds of black coral, here.


If you go to the Galápagos, and even if you go, as I did, in a herd of clumsy American tourists, you will at some point feel like a field biologist. Regulations dictate that you be accompanied by licensed guides, and ours reminded me of my favorite college professors: authoritative and rhetorical most of the time, with sudden bursts of passion when they get a whiff of their pet topic.

Within an hour of my arrival, one of the guides launched into the difference between the islands’ endemic, native and introduced species. Endemic species arrived naturally but struggled to survive in the strange environment. Over many generations, they gradually adapted and are now found, in their modified form, nowhere else on earth. Native species also came naturally, but didn’t struggle as much and didn’t need to change. So they’re found in the Galápagos as well as other places. Introduced species did not “naturally” arrive, but were brought in by people.

My guides seemed to be obsessed with these definitions, mentioning them dozens of times over the course of my eight-day visit. When discussing endemic species — such as the marine iguana or Galápagos tortoise — they beamed like proud parents. But introduced species were the shameful family secret. “What are those trees?” someone asked guide Jason while hiking in the highland swamps of Isabela. “Those are cedars,” he said with a long sigh and a sad shake of his head. “Introduced.”

I rolled my eyes. I understand the concept, professor, really I do, now can we please move on? But, like most of the other times I’ve been annoyed with a good teacher, I was wrong. Several weeks and a lot of reading later, I’m finally beginning to get it. If you understand endemism, you understand the value of the Galápagos.

View Images
Male frigatebirds puff their bright red chests to attract females.

The Galápagos Islands are often called a “natural laboratory” for studying evolution. The archipelago is 600 miles from the mainland and, because of strict laws imposed the past few decades, people are not allowed to live (or even eat) on 9 out of the 14 islands. What’s more, although they all share the same general climate, each island has unique geological features. So the place is isolated, contained; its variables are relatively independent and controlled. Scientists love that stuff.

More to the point: Isolation breeds endemism. A few individuals in a species arrive in a weird new place; they adapt. They rarely encounter compatriots from the mainland to breed with, and so they gradually become more distinct, until they are wholly different. Lots of endemic species — and the Galápagos has hundreds — means lots of opportunities to observe exactly how evolution works.

In other words, the Galápagos is not only a gleaming laboratory, but one brimming with data to be mined.

Darwin, being Darwin, understood this immediately. “The archipelago is a little world within itself,” he wrote in Voyage of the Beaglehe wrote in Voyage of the Beagle. “Both in space and time, we seem to be brought somewhat near to that great fact — that mystery of mysteries — the first appearance of new beings on this earth.”

The photos in this post show magnificent frigatebirds, just one of many examples of the power of endemism in the Galápagos. The birds are klepto-parasitic, meaning that rather than diving for their own fish, they force other birds to give them regurgitated catch. (Ewww.) Unlike those other birds, magnificent frigates lack the oil gland needed to keep their feathers waterproof. If they had it, they’d be too heavy. You see, magnificent frigatebirds have evolved to be exceptional flyers. They have teeny-tiny bodies relative to very large wings, allowing them to fly for hundreds of miles in one stretch.

View Images
Kleptomaniac frigatebirds have been known to steal tourists’ hats. Caves are dark, sheltered and often quiet. They’re seemingly ideal places for a bit of a nap. But for a small Mexican fish, they have done exactly the opposite. As a result of life in dark caves, the blind cavefish has evolved sleeplessness, on at least three separate occasions. They don’t go entirely without sleep, but they doze far less than their surface-dwelling relatives.The blind cavefish (Astyanax mexicanus) is a sightless version of a popular aquarium species, the Mexican tetra. They live in 29 deep caves scattered throughout Mexico, which their sighted ancestors colonised in the middle of the Pleistocene era. In this environment of perpetual darkness, the eyes of these forerunners were of little use and as generations passed, they disappeared entirely. Today, the fish are born with eyes that degenerate as they get older. Eventually, their useless husks are covered by skin.They went through other changes too. For example, their skin lost its pigment so they are all pinkish-white in colour. And now, Erik Duboué from New York University had found that they also sleep less than their relatives on the surface.Duboué works in the lab of Richard Borowsky, who has been studying the blind cavefish for years. The duo noticed that the captive cavefish in their laboratory were surprisingly active at night, and they wanted to know if they didn’t sleep as much.  How do you work out if a fish is asleep? Duboué did it by basically poking them and seeing how long it took them to respond. He found that the fish reacted far less strongly to a gentle poke if they hadn’t moved very much for a minute. At this point, he classified them as “asleep”.Duboué compared blind fish from three separate caves - Pachón, Tinaja, and Molino – as well as one of their sighted surface cousins. He found that the surface fish sleep for an enviable 13 hours a day – mostly at night, with the odd afternoon nap. The cavefish, on the other hand, sleep for just 2-4 hours a day. When they do fall asleep, they’re just as heavily under as their surface cousins, and their movements slow to the same extent. They’re not lighter sleepers – they just get less of it.The cavefish are a fantastic example of convergent evolution, where populations take different routes towards the same suite of adaptations. The Pachón, Tinaja, and Molino cavefish all entered separate cave systems that aren’t connected to one another. They lost their sight, and their sleep, independently of one another.These separate paths became abundantly clear in 2008, when Borowsky bred blind cavefish from different populations and produced youngsters that could see! In a single generation, he managed to reverse a million years of evolution. Borowsky succeeded because the different groups of blind cavefish lost their eyes through different genetic changes. In any one lineage, these changes work together to nix the development of the growing eyeball. But in the hybrids, every altered gene inherited from one parent was compensated by a normal copy from the other.Duboué and Borowsky wanted to see if they could breed cavefish with normal sleeping patterns in a similar way. When they bred Pachón or Tinaja cavefish with surface fish, he found that the hybrids still didn’t sleep very much. When they bred the hybrids with more surface fish, they produced some youngsters that nodded off for long surface-style hours, and some whose sleeping patterns were half-way between the two extremes.This suggests that the shorter snoozes of the cavefish are driven by a combination of altered genes, some of which have dominant effects. Borowsky’s next mission is to find which genes – they might also control the sleeping patterns of humans and other animals.For now, the team doesn’t know why the cavefish have evolved to catch ten winks instead of the standard forty. After all, sleep is important. Aside from the fact that animals perform better if they are well-rested, experiments on humans and fruit flies have shown that sleep is important for solidifying memories. There’s no reason to think that cavefish have less need of alert brains or lasting memories. Instead, it’s possible that they simply cannot afford to sleep any more than they do. They live in realms where food is a rare commodity, and they might need to be constantly on the lookout for it.It will be interesting to see if other cave-dwellers share the same adaptations. After all, many other cave species, or troglobites, share the degenerated eyes, pale skin and heightened senses of the cavefish. In these dark worlds, convergence is king. On that note, as I write this, the time is 1.30am and I am in a dark living room lit only by a dim energy-saving lightbulb. I need to be awake in five hours. See? Convergence...Reference: Duboue, Keene & Borowsky. 2011. Evolutionary Convergence on Sleep Loss in Cavefish Populations. Current Biology ref tbcImage by skpyMore on cavefish: Giant insect splits cavefish into distinct populations Cross-breeding restores sight to blind cavefishMore on sleep To sleep, perchance to dream, perchance to remember Memories can be strengthened while we sleep by providing the right triggers Sleeping on it – how REM sleep boosts creative problem-solving The point of sleep, or, Do fruit flies dream of six-legged sheep?
View Images

Because they can travel so far, frigatebirds swap genes all over the Caribbean and beyond, from the Galápagos to Florida to Baja. This makes them the go-to example of a native species in the Galápagos. And yet…

Last year, researchers from the Smithsonian Conservation Biology Institute analyzed the DNA of magnificent frigatebirds from nine different locations. All had roughly the same genetic make-up, with one exception: the Galápagos magnificent frigates. Turns out this population, which numbers about 1,000 pairs, has been on its own genetic course for half a million years.

How did the islands create this new subspecies (or, perhaps, new species), when the birds could have flown away anytime? Is it because they prefer to breed where they were born? Or because the islands provide especially nutrient-rich prey? Is it a byproduct of increased choosiness for mates with some Galápagos-specific trait? Nobody’s got a clue, but figuring it out will get us closer to understanding Darwin’s mystery of mysteries. The International Union for Conservation of Nature puts magnificent frigatebirds in a category of “least concern.” But in light of the new data, the researchers argue that the birds are worth protecting. Like everything else on the islands, I’d say.


All photos by Randal Vegter

This post was originally published on The Last Word on Nothing