This is one of my all-time favorite examples of the power of natural selection, and one I taught in my evolution class as an example of mimicry. These freshwater mussels have a load of fertilized eggs that produce larvae that feed on fish blood until they’re grown. This poses a problem: how do you get the larvae into the fish mouth, where they can latch onto the fish tissue and feed on blood in the vascularized gills?
This video shows several ways. The first is simple: the mussel latches onto a fish and then forces the larvae into the trapped fish’s mouth, the prime feeding spot for larvae (gills are loaded with blood vessels to absorb oxygen from the water). The larvae develop for a while and then drop off the fish to grow into sedentary adult mussels. This means that the mussels have to let the now-parasitized fish go so they can disperse the young.
The other way—the really amazing way—is found in Lampsilis mussels, who have evolved a brood pouch, containing the larvae, on the edge of the mantle. The brood pouch looks remarkably like a fish, and so a predatory fish approaches to nibble on the pouch. At that moment, the mussel squirts the larvae into the predator’s mouth, where they fasten onto its gills. Instead of getting a meal, the predatory fish becomes a meal, but not one that’s fatal to the fish. Still other mussels release larvae that look like worms or fly pupae and, when gobbled by hungry fish, again latch onto the fish’s blood vessels. Still other mussels put out lures that look like fish and act like the brood pouch, squirting mussel larvae into the mouths of hungry fish.
What’s remarkable in all this is how closely the brood pouch—or the larvae—have evolved to look like food. Mimicry like this is a good way to show the power of natural selection!
For today’s biology lesson as I get my teeth cleaned, here’s a 20-minute video lesson about some salticids—the family of jumping spiders—that mimic ants. As you’ll see, this resemblance appears to be a form of Batesian mimicry, in which the spiders mimic toxic, unpalatable, or dangerous ants. The remarkable near-perfection of this mimicry, in which many features of the spiders have been modified to look like ant features, shows how closely natural selection can take an organism to its “optimum” phenotype. (Mimicry is one of the feat aspects of organisms in which you can judge how close they come to the “optimum”: in this case the organism or aspect of the environment they’re imitating.) It also shows the ubiquity of genetic variation, which must, during selection, have been present for every one of the modified features.
And it’s not just morphology that gets imitated, either. There’s chemical mimicry in this case, and behavioral mimicry (e.g., how the spider holds its legs in an antlike position).
The YouTube notes say this:
An exploration of jumping spiders that mimic ants (aka Ant-Mimicking Jumping Spiders) framed around a discussion with spider-scientist Alexis Dodson of the University of Cincinnati’s Morehouse Lab.
Matthew and I love mimicry, as it instantly shows the “creativity” of natural selection in a way that few other adaptations can. And it’s so diverse: note that there’s also audible mimicry, smell mimicry, and even “vibrational” mimicry, none of which can be seen by just looking at an animal’s appearance. We’ve only scratched the surface of the diverse ways that animals (and plants) can pretend to be something that they’re not.
This is the best ZeFrank video I’ve seen. Not only are the videos absolutely stunning, but it’s biologically accurate. (I found only one tiny error; can you spot it?) It’s not as funny as ZeFrank’s other videos, but to a bio nerd, it’s stunning. Do watch it, and if you’re not amazed at nature’s largesse, you have a heart (or brain) of stone.
Many of the images in the video are taken from here.
Some of the most fascinating observations in biology, at least to me, involve the comandeering of one species by a parasite, who take the host over, changing it in a way that facilitates the parasite’s own reproduction. “Zombie ants“, infected by a behavior-altering fungus, are one example, and some people think that the protozoan Toxoplasma gondii, which humans get from cat feces, changes the behavior of rats when it infects them, making the rats lose their evolved fear of cats. The infected rats then are more readily eaten by cats, thus facilitating the reproduction of the protozoan, which becomes infectious when it gets into the cats and exits through their feces. Any mutant protozoan with the tendency to make rats less afraid of cats will be more likely to be passed on, which of course is positive natural selection. But in neither that case nor the case of zombie ants infected with fungus do we know exactly how the parasite commandeers the host and changes their behavior. Working that out will be a fascinating task.
Today we have another fungus that affects its host in a way detrimental to that host but good for the fungus. The system is described in a new paper in Fungal Genetics and Biology (click on screenshot below, full reference at the bottom), or find the pdf here. There’s also a summary in Scientific American.
Now there are a couple of cases known of fungi that actually take over a plant host’s development and produce pseudoflowers that attract insects. Those pseudoflowers, while made of plant material, are also covered with fungal hyphae. The fungus also somehow induces the plant to produce a nectarlike substance. Both the pseudoflower and nectar attract pollinating insects, who instead of getting pollen get covered with fungal spores. The spore-covered pollinators then move to a new infected plant. This is a way the fungus manages to disperse its genes and also (some fungi have “sexes” or mating types) effect matings with another fungus on another plant. It’s a form of fungal reproduction, just as pollination is a form of plant reproduction.
In today’s case we have something a bit different: the fungus, when infecting the plant, itself assumes the form of a flower that looks remarkably like the host flower. It also develops pigments that are known to attract insects, including those in the UV light spectrum. Finally, the fungus appears to emit volatile chemicals that are identical to some chemicals of the host flower that attract bees.
Did I mention that the fungus also sterilizes the host plant (a flowering grass), so that the fungus doesn’t compete with the grass flowers for pollinators?
Click to read:
The two species of grass that the fungus infects were found in western Guyana, and are “yellow-eyed grasses,” Xyris setigera and X. surinamensis. Both are infected with the fungus Fusarium xyrophlium, a new species described by these authors. When it infects the grasses, the fungus sterilizes them, so that they produce no flowers or mature fruit, and the fungus sets up a systemic infection of the grass plant. Infections are patchy in Guyana; not all grasses have them and most grasses don’t.
After a plant has been infected for a certain time, the fungal hyphae grow into a “pseudoflower” at the grass tip that is a remarkable mimic of the grasses’ own flowers. Have a look at this figure from the paper. The first three photos show the fungus “flower”, and only the last shows the grass’s own natural flower. Again, the faux flower in the three photos at the left is made of pure fungal hyphae; it’s not made of plant cells “directed” by the fungus to assume the configuration of a flower, as in other cases.
Do the faux flowers attract insects? Yes, they were observed to attract small bees, though the flowers weren’t watched very long.
Do the bees carry spores that they get from trying to extract nectar from the fungus? We don’t know. The fungus is “self-sterile”, having different mating types, so it’s likely that these false flowers have evolved to not only disperse the fungus, but to facilitating its mating, since the spore-laden bee would likely be duped again and, in so doing, bring together two spores that could effect a mating.
Do the same bees pollinate the real flowers and the fake ones? That’s essential, for the mimicry involves duping the regular pollinators. Again, we don’t know. Note, though, that the faux flower has the same general shape and color as the real flower.
It’s interesting to note that, besides sterilizing the grass, the fungus seems to have no other detrimental effect on it. That’s what the fungus “wants,” of course, for its propagation depends on not killing off the grass, which is a perennial.
Bees not only see in the visible light spectrum, but also in the UV. The authors extracted pigment compounds from the fungus and found that there were indeed pigments in them that fluoresce in the UV spectrum. Thus bees could see more than just what we do. But we don’t know how the faux fungus flowers look to the bees, or whether bee vision makes the faux flowers resemble the real grass flowers. (There are many unanswered questions raised by this study.)
Finally, the authors looked at the volatile compounds of the fungus and flowers to see if they had anything in common; that is, was the fungus mimicking the odor as well as the appearance of the flower? Because the authors couldn’t get back to Guyana because of the pandemic, they used a related flower, X. laxifolia from North Carolina, compared to the lab-cultured fungus. Gas chromatography revealed only one volatile compound in common between the fungus and the grass flower: 2-ethylhexanol. This compound, however, is known to be a fairly powerful attractant of bees.
While many questions remain hanging, they can in principle be answered, and this paper describes a unique system: another weird way evolution works. Here are some of the questions remaining:
a.) Did the fungus independently evolve its ability to produce faux flowers on both species of grass? (I would guess not.)
b.) Do the pollinators really move spores between infected grasses? (My guess would be yes; why else would the fungus evolve such an elaborate ability to make mimetic flowers?)
c.) What it is about infecting a grass that makes the fungus suddenly able to form flower-like shapes? Does some compound or gene in the grass itself induce the fungus to do this?
d.) How similar does the grass flower appear to the fungus “flower” to the eye of a bee?
e.) What other compounds of the fungus “flower” attract insects, and are they similar to odorants from the grass flower?
As Orgel’s Second Rule of Biology states, “Evolution is cleverer than you are.” And in this case it’s been very clever!
Over five years ago I wrote about a remarkable adaptation in insects: mimicry of snakes. Remember that “holometabolous” insects go through very different life stages, and this includes Lepidoptera, which have larvae that become pupae (also known as “chrysalises”), and out of those pupae hatch the winged adults. The larvae (“caterpillars”) are often highly edible to birds and other predators, and have to evolve various strategies to avoid being eaten. Snake mimicry is one such strategy.
In 2020 I described one example of a caterpillar mimicking a snake. When the caterpillar is disturbed, it displays a remarkably snakelike underside and rears its head like a venomous snake. This is the Snake-mimic caterpillar, Hemeroplanes triptolemus, a moth from the Amazon rainforest found in Puyo, Ecuador. The video was taken by the late Andreas Kay, who rediscovered my frog Atelopus coynei. (Kay’s photos are now curated by reader Lou Jost.) I’ve put Kay’s video below again—it’s the second one in this post.
But pupae, being immobile (well, as you’ll see, they can sometimes move a little), have a bigger problem, for they don’t have much behavior to deter predators. In another post from 2015 I described and showed some photos of a pupa that, like the caterpillar above, also resembles a snake. (It’s a different species from the one above; the pupal mimic becomes a butterfly while the larval mimic turns into a moth.) I also noted that the pupa could actually move a bit, and it’s likely that even a little motion might deter a predator. But at that time I had no video to show.
Recently I found that in fact Kay did take some video of the snake-mimic pupa and had put it up in 2018. Ergo, just below, in the top video, you can see a pupa that resembles a snake. The resemblance of both moth and butterfly mimics is so close to that of a snake, both morphologically and behaviorally, that it’s hard to think of any explanation other than Batesian mimicry.
First, here are Andreas’s YouTube notes:
This chrysalis or pupa of the Daring Owl-Butterfly, Dynastor darius, was filmed in the Jardin Eco-botanico Mindo, Ecuador. It mimics the head of a snake which gives it an advantage in the struggle for survival by scaring off predators such as birds. It has fake eyes, a fake mouth, fake scales and even strikes like a snake if disturbed, as shown in this video.
And look at it move! How does the immobile and developing butterfly adult know that something’s threatening it? It appears to have a sense of touch.
And here again is the moth larva mimicking a snake; a video I showed before. You might want to ponder the incipient stages of this adaptation—what were the first snake-resembling features to evolve?
Tony Eales from Queensland weighs in with photos documenting a nice story of parasitism and mimicry, with the mimicry being an orchid that deceives a male wasp into trying to copulate with it. (The gain is pollination for the flower; the wasp gets nothing but frustration.)
Tony’s descriptions are indented; click on the photos to enlarge them.
I came across something quite special on the weekend. It’s a terrestrial orchid Arthrochilus prolixus, AKA Wispy Elbow Orchid.
This orchid by sight and smell imitates a wingless female Thynnid wasp. Female Thynnids often sit at the top of a blade of grass waiting for a male to find them. It is this behaviour the orchid takes advantage of.
JAC: Note how the orchid above imitates a waiting female. The male mates with the orchid, getting pollen on its back, and then, because wasps aren’t that smart, eventually tries to mate with a different orchid, whereupon the pollen from the first orchid detaches and pollinates the second one. (Note the stamens in the orchid at lower right above.) This is known as pollination by “pseudocopulation.”
Thynnid males pick up females and carry them around while mating for many hours.
Thynnids are parasitoids of scarab beetle larvae. Scarabs live under ground or within litter for a year or more, feeding and growing. As larvae they are often known as Curl Grubs (and I realise I don’t have any photos of curl grubs which is strange, only adults). [JAC: see a photo here.]
The females deposit a single egg on any scarab larvae they find which grows and eats the larvae until emerging as an adult wasp and digging out.
Here’s a photo of a male I observed busily pulling back leaves off the ground as a newly emerged female was making her way out.
There are around 2000 species of Thynnid in Australia of which only about a quarter have been described and named. As far as I can tell no-one yet knows the species that pollinates the orchid that I found.
Tony Eales from Queensland came through with three batches of photos. Today we see the first one, whose theme is a subject dear to my heart—mimicry. Tony’s notes and IDs are indented; click photos to enlarge them.
Remember that in Batesian mimicry an edible “mimic” evolves to resemble a visible and toxic or dangerous “model,” protecting the former from predation by a third, predatory species that has either learned or evolved to avoid the model. In Müllerian mimicry, on the other hand, two toxic or distasteful species evolve convergently to resemble each other, which gives a selective advantage for the survival of each: it’s easier for a predator to learn and avoid one pattern rather than two.
Some recent examples of mimicry that I’ve photographed.
The first two are an example of Müllerian mimicry. Both the Velvet Ant (actually a wingless female wasp) Aglaotilla sp. and the Green-head Ant (Rhytidoponera metallica) possess a pretty nasty sting and inhabit the same habitat, leaf litter and tree trunks. A predator’s experience with one will inform their future interactions with the other.
Next is an Ant-like Flower Beetle, Anthelephila sp. which are Batesian mimics of ants. They are not close mimics but the ant-like shape and the colour patterns are similar to many ant types— e.g., these Iridomyrmex purpureus Meat Ants—and probably confers some advantage. Given how common and varied ants are in the Australian bush, predators probably tend to just ignore anything ant-like.
The next two are beetles mimicking beetles. Episcaphula rufolineatais in a group called the Pleasing Fungus Beetles (family Erotylidae) which, as the name suggests, feed on fungus and are often quite colourful.
Scaphidium exornatum, on the other hand, is in the Scaphidiinae, the Shining Fungus Beetle sub-family of Rove Beetles. It also is found feeding on fungus in the same forests as E. rufolineata.
As you can see, they look very, very similar and without knowing what chemical defences either have, it’s hard to know if this is Batesian or Müllerian and which species was the model and which the mimic. S. exornatum doesn’t look like a typical Rove Beetle, but there are some strange looking Rove Beetles without any mimicry going on (try Googling Diatelium wallacei some time).
Not only are these two mimics not in the same beetle family, they are in different infraorders.
The next set of beetle mimics broke my brain. I don’t even know what is real any more. Lycid beetle mimicry is very common, among other beetles and also insects as different as flies and moths but the mimicry here is so perfect, I’m reluctant to ID another Lycid.
Trichalus ampliatus is a fairly common lycid beetle where I live, known as the Red-shouldered Lycid Beetle. I photographed one just the other day and put it up on iNaturalist as T. ampliatus only to be informed that no, what I was looking at was a member of the False-blister Beetle family Oedemeridae. To me the only difference I can see is the mouth parts. The texture of the wing covers, the look of the antenna, the colour, even the way it holds itself is a perfect match. Fittingly the genus is Pseudolycus.
Last, a case of aggressive mimicry. [JAC: An animal evolves to further its aggressive behavior; in this case, a predator evolves to resemble its prey to fool them.]
The larva of the small ladybird known as the Mealybug DestroyerCryptolaemus montrouzieri looks like a mealybug or scale insect. These bugs suck plant juices and excrete sugary waste that ants collect. The ants in turn defend the mealybugs from predators. But the Mealybug Destroyer larva looks like a mealybug and perhaps smells like one too. In addition, the waxy filaments are a good defence against ant aggression as well as protecting these insects from over-enthusiastic ant attention.
The pictures of leaf insects below come from a cool science story in the New York Times about this fabulous family of fantastic mimics (Phylliidae). The story has a lovely twist, as the females look like leaves while the males look like sticks, and for many years scientists thought the sexes were members of different species. In fact, they were named as different species. There’s one clue that something’s amiss, though: you shouldn’t find that every individual of your species is a female—or a male.
There are only three ways to identify such different-looking sexes as members of the same species. First, you can catch a male and female in copulo. That isn’t on for these species, as the sexes are both hard to see—so cryptic that some experts on the group have never seen a living individual in the wild.
Second, you can look at the DNA, for males and females should have virtually identical DNA—much more similar than the DNA of different species, even closely-related ones.
Third, you can do what was done in this case: rear a clutch of eggs in the lab, and discover that from that clutch both sexes, having drastically different appearances, emerge. And that’s how they identified the conspecific males and females in this case. Do read the story at the link above.
For our purposes today, you can see the preciseness of female mimicry by looking at the photo below. It contains nine leaf insects. Your task, which isn’t easy, is to find them all.
The reveal will be at 3 pm Chicago time. (The photo is by Hsin-hsiung Chen.) Click the photo to enlarge and make hunting easier.
Just to show you what these marvelous mimics look like, here’s a close-up of one (caption from the NYT article):
The first paper below is five years old, but I just read it yesterday because it’s a remarkable example of mimicry. In this case, seeds of a plant in South Africa have apparently evolved a size, shape, appearance AND smell that makes them resemble antelope droppings. Dung beetles, thinking that the seeds are fecal matter, roll them to a safe place and bury them, ensuring that the seeds are protected, dispersed a bit, and get planted. The paper, from Nature Plants, is below (click on screenshot), the pdf is here, and the reference is at the bottom. (If the article is paywalled, a judicious inquiry will yield it.)
This is one of the very few examples in which plant seeds have evolved to deceive animals, either physically or chemically, and in which the plant benefits but the animal loses. This is, in fact, the evolution of a plant that parasitizes an animal.
Here’s a later paper (2016) from the South African Journal of Science with a free pdf (click on screenshot):
The plant that’s evolved mimicry is Ceratocaryum argenteum, a shrubby plant that’s endemic to the Cape Province of South Africa:
Unlike seeds from other plants in the family Restionaceae—which are normally pretty flat, with a smooth, dark seed coat as well as elaiosomes (fleshy bits that are edible to ants, who carry the seeds to their nest, feed the elaiosomes to their larvae, and then discard the rest of the seed, which thereby gets dispersed)—C. argenteum has a “rough tuberculate and brown outer seed coat” which, to the authors’ noses, “has a pungent scent similar to herbivore faeces”.
Below: what the seed looks like (a-c) in contrast to other seeds in the area (h-j). (g) shows the dung of an antelope (a Bontebok). Note that the C. argenteum seeds are about the size and shape of the Bontebok dropping, and are round to facilitate rolling. Dung beetles roll balls of dung to a nearby location, bury them, and lay an egg with the dung so its larvae can feast on the feces. The beetle observed burying seeds was Epirinus flagellatus.
And the dung-maker, the small antelope most common in the area (80-100 cm or 31-39 inches at shoulder): the bontebok, Damaliscus pygargus pygargus.
The authors hypothesized that the size and smell of the C. argenteum seeds would facilitate them being buried, and so they put out seeds along with some camera traps. They observed four-striped grass mice (Rhabdomys pumilio) eating husked seeds but never burying them. In contrast, of 195 seeds put out after a rain (when dung beetles are active), at least 55 were buried (they used fluorescent threads to mark the seed paths).
In no case did the buried seeds have a dung beetle egg on them, so the beetles were first fooled, and then realized that something was wrong—but only after they had rolled away the seeds and buried them.
As I noted above, resembling dung to fool beetles is a good way to perpetuate your genes, as you get dispersed, protected by the soil from mice, and buried (planted). Further, C. argenteum plants can’t re-sprout after a fire, and thus the persistence of plant genes depends on a way to escape fire—by getting its seeds buried! For many reasons, then, selection might favor the seeds resembling dung, and because beetles detect dung by its odor, you’d want to smell like dung, too. The dung beetles are simply dupes, doing a lot of work and not getting anything out of it.
The authors also did gas chromatography and mass spectrometry to measure the amount of volatile compounds on seeds and dung, and found that the seeds had a significantly larger amount of volatiles than other seeds in the area, even when old and when corrected for surface area, and resembled the amount of volatiles in dung. Further, compounds in the seed volatiles were also identical to compounds in the volatiles of bontebok and eland dung (another antelope), with “various acids, the benzenoid compounds acetophenone, phenol, p-cresol and 4-ethyl-phenol, as well as the sulphur compound dimethyl sulphone.”
Here’s a two-dimensional plot showing the resemblance of the C. argenteum seed volatiles to dung volatiles; note that other seeds (green triangles) don’t have dung-like profile of volatiles:
In the second paper, the authors observed another dung beetle, Scarabaeus spretus, burying the seeds, flying rather than crawling to the piles of seeds put out. (It’s clear that odor rather than appearance is a major attractant, and one S. spretus flew directly into a paper bag of seeds!) This species moved seeds only about a quarter of a meter, while E. flagellatus could move them up to 2 meters away from the pile. (As you see, the dispersal is quite limited!) Here’s a figure showing beetles of both species rolling away the seeds and burying them:
Further, the bontebok eats different kids of grasses from the eland (Taurotragus oryx), a larger species shown below, and the different species of grass have different ratios of nitrogen and carbon isotopes. By looking at the isotope ratios in the beetles (whose juvenile stages eat the dung), and in the antelope dung itself, the authors found that the ratios of the dung beetles (green diamonds and purple triangles) resemble the dung of the eland (light blue triangles) more closely than the dung of bontebok (red circles), as shown in the diagram below.
Conclusion: the dung used by both species of beetles is likely to be from eland rather than from bontebok. But as the authors showed above, the volatiles of both antelope dung are pretty similar, and still resemble the volatiles of the seeds.
The one puzzle is that the size of C. argenteum seeds are more similar to that of bontebok droppings than to eland droppings. Being much bigger, elands have larger scat—about twice as big. But since dung beetles can form smaller balls out of larger droppings, and because it may be too onerous for the plant to produce a seed twice as large as it does, this may not be a problem.
So we have mimicry here that deceives the beetle, who comes to its senses only after it rolls away and buries a seed. In this case it doesn’t adhere to the Who’s dictum, “Won’t get fooled again.” It would be interesting, though, to do lab experiments with dung and seeds to determine if beetles eventually learn to avoid rolling and burying these mimetic seeds. It’s a lot of effort for nothing, and the beetle “knows” it since it doesn’t lay an egg on the seed.