Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
The title of this post – “How extremely stupid not to have thought of that!” – was Thomas Huxley’s response when reading Darwin’s idea of evolution by natural selection. It was also my response, and Jerry’s, on seeing this amazing video of sponges eating.
Every year, I teach students that sponges are animals, and that they eat by wafting water currents through their bodies, with a flagellum situated in structures called collar cells. The flagellum captures tiny organic particles in the water, which are then absorbed into the sponge’s body and used for both metabolism and to make more sponge. Whenever I’ve said this in a lecture, there’s been a tiny voice in my head saying ‘But how strong is that current? Can they really get enough particles to grow? Am I actually telling the truth?”.
Now I know the answer – the current creating by those hundreds of thousands of whipping flagella is amazingly strong, as shown by this simple experiment: you release a dye around a sponge, and see what happens to it. How extremely stupid of me not to have thought of that!
Matthew Inman, producer of the fantastic strip The Oatmeal (including one of my favorite comics, The Bobcats), is lately on a tear by promoting evolution in a sarcastic way and dissing the religious alternative as belief in “Jibbers Crabst,” a Holy Crustacean that breathes fire.
First watch this 11-minute video by Inman that appeared on YouTube on December 5; it’s from BAHFest West 2014, whatever that is. You’ll recognize some of the creationist tropes. It’s a wonderful and absolutely hilarious talk, highly recommended by Professor Ceiling Cat.
Be sure to watch the sign-language woman, too; you’ll learn how to make signs for “priapism” and “persistent erection,” which I think amused the audience no end.
I’m pretty sure he’s an atheist. 🙂
To add insult to injury, Inman sent this out in the latest Oatmeal newsletter:
Inman also put this up, which also appears in his talk above. Nothing riles the faithful more than a definition like this, which in effect is true!:
And so the faithful pushed back. This hilarious interchange between Inman and a reader was posted on Oatmeal’s “Hate mail of the day“:
Here Inman seems to be imitating those psychology computer programs that just spit out programmed answers when you type in stuff about your troubles. (The psychotherapist Carl Rogers behaved much the same way.) Now that’s the way to engage the angered religionist!
There is at least one species of bird that is toxic to predators and shows it off by displaying bright “aposematic” (warning) colors. That one, the hooded pitohui of New Guinea (Pitohui dicrhous), was discovered to be toxic by Jack Dumbacher, one of our grad students at Chicago, and now Curator of Ornithology at the Cal Academy in San Francisco. As I recall, Jack noticed this when handling one of the birds and getting a tingling sensation in his hands. He later discovered that the feathers contain a neurotoxin, probably obtained by eating toxic beetles and spreading saliva over its feathers. Here’s a photo of the hooded pitohui from New Guinea Birds:
We were all amazed when Jack discovered what was the first—and perhaps still the only—case of a toxic bird showing off its distastefulness with bright colors. But now a group of researchers from the U.S. and Colombia have discovered a bird in Peru whose nestlings (but no the adults) are not only brightly colored, but appear to have both the appearance and behavior of a toxic caterpillar that lives in the area. These traits of the nestlings are possible examples of Batesian mimicry, in which an edible species mimics a toxic and brightly-colored one that is avoided by predators who have learned to associate the color and pattern with toxicity. The nestlings thus take evolutionary advantage of the predator’s aversion, and so the resemblance is adaptive and one that is favored by natural selection. The nestling, in effect, mimics a caterpillar that is like a pitohui.
The possible case of Batesian mimicry is described in a new paper in The American Naturalist by Gustavo Londoño et al. (reference and link below). The conclusions are tentative, but the resemblance of the nestling to the caterpillar is amazing. Nestlings are very vulnerable to predation; the authors report that predators destroy 80% of the nests before the young fledge.
First, some movies taken by the researchers to show the resemblance. Here’s the toxic caterpillar from Manu National Park in Peru:
Now have a look at the presumed mimicry of the nestlings of Laniocera hypopyrra, the “cinerous mourner”; this is their behavior when they sense movement nearby (like the bird below, the caterpillars also move their heads from side to side).
Note too how different the juveniles look from the adults. They’re orange and covered with white-tipped filamentous feathers, while the adults look like this:
Cinerous mourner adult
The huge difference between the appearance and color of the nestlings versus adults suggests that the nestlings have evolved to have that bizarre plumage for reasons that enhance their survival. It had been suggested earlier by other workers that the nestlings’ appearance might reflect selection to mimic a caterpillar, but such an insect hadn’t been found. It had also been suggested that the color could resemble moss-covered fruits or dead leaves, and so would provide camouflage rather than enhanced visibility.
Here, from the paper, is a picture of a one-day-old nestling, both by itself (left) and with an unhatched egg.
The authors note the distinct plumage of nestlings, shown below at day 9 (left) and day 14 (right):
At hatching, the Laniocera hypopyrra nestling was covered with orange down (fig. 1a), a very different plumage coloration compared to that of gray adults. Each downy feather had 1–10 elongated orange barbs (fig. 2), each of which had a bright white tip (figs. 1, 2). These plumage characteristics are unique among the 120 species of nest- lings we have observed at this study site. Unlike most altricial nestlings, the L. hypopyrra chick did not beg immediately when the parent arrived at the nest with food. Similarly, when we took the nestling out of the nest for measuring, it did not beg for food as other nestlings do. In another uncommon behavior among altricial birds, the parent spent long periods of time at the nest rim after arriving with food but before delivering the food to the nestling.
This delayed begging behavior may reflect the fact that the nestling doesn’t know if the arriving bird is a predator or a parent, and so performs the default “caterpillar” behavior to scare off the former. Parents are presumably used to the behavior.
Below are the chick at day 18 (left) and the caterpillar, a larva of a flannel moth (family Megalopygidae), so called because the adult moths are fuzzy. The species is unidentified, I think, but some caterpillars in the family are known to be toxic. The authors further emphasize the resemblance:
The caterpillar we encountered measured 12 cm, which closely matches the size of the L. hypopyrra nestling (14 cm during the first 14 days); but the striking morphological similarity is the caterpillar’s orange “hairs” with white tips, which match almost exactly the nestling’s elongated orange downy feather barbs with bright white tips. The morphological appearance of an aposematic caterpillar was rein- forced by behavior: the caterpillar-like head movements of nestlings (when disturbed) closely resembles the movements of the aposematic caterpillar.
Here the authors show the unusual barbs at the tip of the feathers, which enhance its resemblance to the caterpillar.
And a final picture of the bizarre nestling, which loses this appearance when it gets older and molts its juvenile plumage.
Now this is only a suggestive resemblance, but it’s pretty amazing, and if true would be the first bird to show Batesian mimicry of any toxic species. Several questions remain to be answered, though, before we regard this as a strong case.
Is the caterpillar really toxic and avoided by birds because of its appearance?
Does the same predator eat caterpillars and also bird nestlings? If it didn’t, then there’s no possibility that the nestling’s appearance helps it avoid predation by birds that have learned to avoid caterpillars. The authors don’t suggest any possible predators, but those would have to be both carnivores and insectivores.
Is the nestling toxic, too, so that it might really be a case of Müllerian mimicry, in which different toxic species evolve the same pattern because it facilitates predator learning and avoidance? The authors suggest that this is unlikely as the juveniles aren’t fed any insects that are toxic and whose poisons it could incorporate into its body.
Does the resemblance of the nestling to the caterpillar really enhance its survival? This would be tough to answer, but could be tested in the lab by presenting putative predators who have learned to avoid the caterpillar with nestlings of various species and appearances. If predators avoided the juvenile cinerous mourners more often, that would be evidence that this is is indeed a case Batesian mimicry (if the juvenile isn’t itself toxic).
Could the appearance serve multiple functions, being both aposematic and cryptic (mimicking moss-covered fruit or leaves) at the same time?
For the time being, then, we have a good natural-history observation that is very suggestive of Batesian mimicry, but needs further research to substantiate it. I suspect, based on the resemblance, that it is indeed the first known case of Batesian mimicry in a bird, and that is simply an amazing thing to see—especially because what has evolved is not just the nestling’s appearance, but its behavior.
First, two photos of bald eagles—named Desi and Lucy—from Stephen Barnard of Idaho. The second one came with a caption.
Stephen’s caption for the photo below: “I dunno. What do you wanna do?” (ref. Disney’s Jungle Book vultures)
Jacques Hausser, a biologist in Switzerland, sends flies (yay)!
I send you four batches of hoverfly pictures (in four separate emails). Here is the first one. I think my identifications are OK, but I’ll not put my life at stake for them.
JAC note: I’ll put the other three batches up in coming weeks. Hoverflies or syrphids, are flies (in the family Syrhpidea, order Diptera). They are also called “droneflies” (perhaps because many resemble bees) and also “flower flies” since the adults live on nectar and pollen. Note that several of these look like bees or wasps, and are almost certainly Batesian mimics of those species, having evolved so that predators will mistake their patterns for those of stinging insects and thus avoid the flies. A paper in Proc. Roy. Soc. in 2000 suggests that some species have also modified their behavior, flying like bees to further this deception. Remember, though that flies have two wings (“Dipteran” means “two-winged”), while hymenopterans like bees and wasps have four. But predators can’t count, especially when the wings are moving!)
Meliscaeva cinctella:
Syrphus ribesii:
Chrysotoxum festivum:
Eristalis tenax:
Finally, a bird from reader Tim Anderson:
This willie wagtail (Rhipidura leucophrys) is taking a drink on the fly, Tumut, New South Wales. It also takes flies on the fly.
It’s Hump Day, and, like the past two days, it’s been miserable, cold, and drizzly in Chicago—but we have still had no snow. The same is true in Dobrzyn, though there’s been some a bit of snow and the Vistula is frozen. Here Hili helps out Cyrus (she can slip though the bars just fine, though it’s getting harder with her recent weight gain).
Cyrus: So what was the Garden of Eden like?
Hili: It was small and fenced off. I will call them to open the gate for you.
In Polish:
Cyrus: Jak to było z tym Rajskim Ogrodem?
Hili: Był mały i ogrodzony płotem. Zaraz ich zawołam, żeby ci otworzyli bramę.
I didn’t quite understand this dialogue, which was, as are all of them, composed by Andrzej, so Malgorzata explained it to me:
Explanation: Cyrus thinks that our garden is THE Garden of Eden. He heard something that there is another Garden of Eden in the Bible and he asks erudite Hili what was the story with the other Garden. She explains that it was too small and limiting for big animals (humans included but not for such nimble creatures like cats – fences are no hindrance for them). So, she is going to help Cyrus to freedom from his Garden of Eden by calling us to open the gate for him.
It’s been a long day, what with preparing to leave and all, but there’s some good news at the end of it. A short article in the Guardian reports that a British judge has ordered that the child of two Jehovah’s Witnesses, a child suffering from bad burns, undergo a transfusion. As you may know, the Witnesses refuse transfusions because of two Biblical verses abjuring the “eating of blood.” (They will allow transfusion of some components of blood, like hemoglobin, which of course means they’re cherry-picking even those verses.)
What struck me is how polite the judge was. I’m not sure I’d have been able to restrain myself in the face of such religiously-inspired stupidity:
[Mr. Justice] Moylan said he hoped that the boy’s parents would understand.
“I am extremely grateful to [the boy’s] father for so clearly and calmly explaining to me the position held by himself and [the boy’s] mother,” said the judge.
“I have no doubt at all that they love their son dearly. I also have no doubt that they object to the receipt by [their son] of a blood transfusion because of their devout beliefs. I hope they will understand why I have reached the decision which I have, governed as it is [their son’s] welfare.”
I talk about this issue in detail in The Albatross, and, after reading about many such cases in the U.S. in which children, enduring or abiding by their parents’ religious beliefs, died, I am struck by two things. The first is that the parents usually either get off scot-free or are given a legal slap on the wrist, although if they withheld medical care on other than religious grounds they’d be punished severely for child abuse, mistreatment, or neglect.
The second is that although these parents insist that they are good parents, they show a striking lack of affect concerning the death of their child. Time after time I’ve read about parents martyring their child for their faith, and then showing no remorse at all about it—often ascribing the child’s death to “God’s will”. There are often no tears and no second-guessing.
Such are the dangers of faith. The parents say they loved their children, but they love their imaginary god more.
Here’s a slide I use in my talk about science vs. faith; the pictures, portraying dead children (who refused blood) as glorious martyrs, “Youths Who Put God First”, comes from an issue of the church’s Awake! magazine from 1994. Every child pictured died from refusing transfusions.This is about the sickest religious propaganda I’ve seen:
