“Everyone’s just lying to everyone”: ZeFrank on mimicry

March 4, 2021 • 2:30 pm

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.

h/t: Matthew

Nefarious fungus mimics a grass flower to facilitate its own transmission

February 14, 2021 • 12:30 pm

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.

(From the paper): Fig. 1. Comparison of Xyris flower and Fusarium xyrophilum pseudoflowers collected in the Cuyuni-Mazaruni region of Guyana in 2010. (A) Young yellow-orange pseudoflower produced by F. xyrophilum emerging at tip of cone-like spike of Xyris surinamensis. (B) Mature pseudoflower of F. xyrophilum enveloping the entire X. surinamensis spike. (C) Longitudinal section of X. surinamensis spike showing partial fruit development in center and pseudoflower of F. xyrophilum. (D) Healthy yellow flower of X. surinamensis shown for comparison, with lateral petals and prominent erect hairlike staminodes. Scale bar: A–D = 5 mm. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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!

h/t: Jean

____________________

Laraba, I., S. P. McCormick, M. M. Vaughan, R. H. Proctor, M. Busman, M. Appell, K. O’Donnell, F. C. Felker, M. Catherine Aime, and K. J. Wurdack. 2020. Pseudoflowers produced by Fusarium xyrophilum on yellow-eyed grass (Xyris spp.) in Guyana: A novel floral mimicry system? Fungal Genetics and Biology 144:103466.

A remarkable pupa that resembles a snake—and moves!

January 20, 2021 • 1:30 pm

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?

Readers’ wildlife photos

January 20, 2021 • 8:30 am

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.

Here’s a good article on Australian Thynnids for the layperson.

And here is a paper describing how a different species of elbow orchid tricks the wasps into getting a wad of pollen attached to the right spot on their back with great pictures.

Readers’ wildlife photos

January 4, 2021 • 8:00 am

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.

 

Meat ants:

The next two are beetles mimicking beetles. Episcaphula rufolineata is 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.

T. ampliatus:

Pseudolycus sp.:

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 Destroyer Cryptolaemus 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.

C. montrouzieri:

Mealybug:

Here are the leaf mimics!

December 7, 2020 • 3:00 pm

Did you spot all nine leaf insects in today’s photo from the New York Times taken by Hsin-hsiung Chen? Here’s the reveal (click photo to enlarge):

If you can’t see them, it’s a clue that sharp-sighted birds, who hunt these using vision, can’t easily see them either.

Spot the leaf insects!

December 7, 2020 • 12:30 pm

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):

A female Phyllium asekiense, a leaf insect from Papua New Guinea. Like many leaf insects, P. asekiense was known only from female specimens.Credit: Rene Limoges/Montreal Insectarium

h/t: Jean

Plant seeds evolve to mimic antelope droppings, and dupe dung beetles roll and bury the seeds

December 3, 2020 • 9:30 am

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.

ac, Vertical (a) and side (b) views of a C. argenteum seed as well as one that has been cracked open (c) showing the endosperm and thick woody inner seed-coat layer and the outer tuberculate layer which together form the husk. d,e, Scanning electron microscopy (SEM) of the outer, tuberculate layer and inner seed-coat, with white silicon granules at the boundary between the two layers. fE. flagellatusg, Bontebok faeces. h,i, Vertical (h) and side (i) views of an L. sessile seed. jCannomois grandis seed with white elaiosome.

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:

(from the paper): Similarity in the composition of volatile blends of seeds and animal droppings is based on non-metric multidimensional scaling. Symbols for other Restionaceae (Methods, Supplementary Table 3) that overlap are slightly offset for clarity. The composition of scent sampled from Ceratocaryum seeds is very similar (R = 0.75, P = 0.33) to that of dung of local herbivores (eland and bontebok), but differs markedly (R = 1.0, P = 0.028) from that of seeds of other Restionaceae (nested ANOSIM permutation test).

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:

(a) Epirinus flagellatus rolling a Ceratocaryum argenteum seed; (b) Scarabaeus spretus rolling a seed (the arrow indicates a Sphaerocerid Lesser Dung Fly); (c) the large hole made by Scarabaeus spretus for burying several seeds (the arrow indicates the location of the Dung Beetle); and (d) a female Sarcophagid Fly on a seed. Midgley & White (2016).

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.

An eland:

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.

h/t: Jean

_____________

J. J. Midgley, J. D. M. White, S. D. Johnson and G. N. Bronner. 2015. Faecal mimicry by seeds ensures dispersal by dung beetlesNature Plants 1, 15141, https://doi.org/10.1038/nplants.2015.141

 

Heavy human harvesting of a valuable medicinal plant leads to evolution of new leaf and flower colors

November 22, 2020 • 10:30 am

If humans harvest an animal or plant, especially if they harvest it heavily, the species often evolves to make itself less “harvestable”.  For example, commerical fisheries that take the larger fish in the sea have led to the evolution of individuals that mature earlier at a smaller size, for it is the small reproducing fish who don’t get caught. Elephants harvested for their ivory have, in some populations, evolved smaller tusks or even tusklessness, for it’s the tuskless elephants who leave more offspring. (The condition for all such evolution, of course, is that the evolved conditions have at least a partial genetic basis.)

Finally, there’s a similar phenomenon called “Vavilovian mimicry”—named after the great Russian geneticist and botanist Nikolai Vavilov, who was imprisoned by the Soviets and died in the gulag because he dared to embrace Western genetics and science against the teachings of the charlatan Lysenko.

In Vavilovian mimicry, weeds are selected among agricultural crops with which they grow to get themselves in the next generation of the crop. Farmers have mechanical ways to sort out the weed seeds during harvesting, and this imposes selection on the weeds to produce seeds of the same size and shape as the crop; it’s those mutant weed seeds that get replanted the next year.

A cool and famous example is how the common vetch (Vicia sativa), a weed, has evolved in crop areas so that its seeds come to closely resemble that of the edible lentil (Lens culinaris), a crop that the weed infests.  Because lentil seeds, which are what’s eaten, are tasty but vetch seeds are bitter, farmers have used mechanical and visual sorting to discard the wild vetch seeds. Over time, the vetch seeds have undergone what’s called “unnatural selection” (for Vavlovian mimicry) to have the same size, color, and shape (flattened) as the lentil seeds. Here’s a diagram showing the cultivated lentils (A) along with the wild vetch seeds growing on their own (B), and the seeds of the same vetch, but which have grown in lentil fields. Look at the big evolutionary change in the vetch seeds!:

Today we have another example of plants mimicking other things—in this case the environment—to hide themselves from being harvested.  Fritillaria delavay, is a perennial alpine Asian plant that grows from a bulb, living about five years. The bulbs, particularly the small ones, are very prized in Chinese medicine, especially for treating tuberculosis, fetching up to nearly $500 per kilogram. (Since they’re small, it takes about 3,500 bulbs to make a kilogram.) They are picked visually, with harvesters looking for the bright green leaves and flowers of the plant that stand out against their rocky background.

Since harvesting is heavy, you can guess how the plant evolved. That evolution is documented in this new paper in Current Biology (click on screenshot below, or go here to get the pdf, both of which are free).  If you want a journalistic summary, there’s one in the Times and another in the Guardian.

In short, the plant has undergone evolution of both leaf and flower color to make it more inconspicuous and thus harder to find and harvest (harvesting, since it takes the bulb, kills the plant). You’re more likely to reproduce if you’re not seen, and in harvested areas those plants with mutations making them match the background better are those that survive. Herbivores apparently aren’t involved in this system, as nothing has been observed to eat the plant, which is full of alkaloids and toxic.

Here are pictures F. dlavayi in an unharvested area (left) and one in an area heavily harvested (right). You can guess which is which. Note the difference in the color of both leaves and flowers. In fact, the green color can evolve to either reddish, brownish, or grayish colors depending on the color of the background.

 

In the paper, the authors collected plants from eight populations in southwest China, and found significant divergence of color among the populations using a special “vision model” to measure the colors and luminescence seen by humans. Here’s a plot of the variation among the eight populations (each dot has a color that is related to the plant color, with each color representing a single population):

(From paper): Plant Color Variation of Fritillaria delavayi among Populations. (A) Color divergence from eight populations in human CIE L∗a∗b∗ color space

Are the plants camouflaged in their local area, and is the degree of the camouflage correlated with how heavily the plants are harvested? The authors derived a measure of how camouflaged a plant was by comparing leaf and flower color with the color of the soil or rock background (also measured using the human-vision algorithm). Collection intensity was assessed by questioning the locals and deriving an estimate of intensity = [amount of bulbs collected]/[relative abundance of the plant in the area]. The higher this fraction, the heavier the collection effort (i.e., the proportion of the population that gets taken by collectors).

As you see from the plot below, the higher the collection intensity in a population (position to the right), the better the mimicry (lower values on the Y axis). The relationship is highly statistically significant (p < 0.001). Clearly, the prediction that the color evolved in response to human harvesting is supported.

Finally, the authors looked at an ancillary relationship: that between the difficulty of digging up bulbs (some are hidden under dirt and rock piles) and the degree of camouflage of the population. The relationship they found is shown below. One predicts that the easier it is to dig up a bulb, the more camouflaged the population would be, for easier digging makes for heavier harvesting and thus stronger “unnatural selection”. The relationship below affirms the prediction, though they left out one population where collection is easy but the plant is green—yet collection isn’t heavy in this population. (This sounds like post-facto discarding of data, but could be kosher.)

Whether each dot is statistically independent of the others, which seems to be the assumption when doing the nonparametric correlations, is dubious, since plants in a given area are related to one another, and each plant didn’t evolve its color independently—the population as a whole evolved its color as a gene pool.

Leaving that possible quibble aside, the authors finally did a computer experiment on target slides showing plants matching their background to various degrees. They found, as expected, that the locals took longer to detect a plant when it matched the background, confirming that your chance of escaping “predation” is likely higher when you’re better camouflaged.

Here’s one more photo from the paper showing the cryptic nature of the plant in brown and gray backgrounds (C and D), and how readily the bright green plants stands out against a scree background (A and B; this is clearly a low-harvest area).

Plant Color Variation of Fritillaria delavayi among Populations

There are no new principles demonstrated in this paper, but the results are still fascinating, and show a mixture of artificial and natural selection that’s called “unnatural selection.” That is, the color isn’t a deliberate product of the breeder, like the grotesquely long bodies and minuscule limbs of wiener dogs, but is an inadvertent result of “artificial” selection. (I’m not even sure I’d call this artificial selection, for humans are part of nature and are gathering something they need.) And, like natural selection, all this process requires is differential reproduction of individuals that have different genetic variants.

If you want to read more about “unnatural selection” and how it’s affected many species, click on the screenshot below.

h/t: Ben, Matthew, Florian

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Niu, Y., M. Stevens, and H. Sun. 2020. Commercial Harvesting Has Driven the Evolution of Camouflage in an Alpine Plant. Current Biology. Online. https://doi.org/10.1016/j.cub.2020.10.078

A beautiful planthopper that mimics an ant (with a twist)

July 17, 2020 • 10:00 am

Planthoppers are in the order Hemiptera—the “true bugs”—along with cicadas and aphids, and are in the suborder AuchenorrhynchaI’ve written about them before: they have all kinds of bizarre appearances that sometimes defy explanation (e.g., these ones).  In 2012 I wrote a report about a strange planthopper (Formiscurra indicus) that mimicked an ant, but the kicker was that the mimicry was described as being limited to one sex: the males. The females looked pretty much like “normal” planthoppers.

Sex-limited mimicry is known in some species, like butterflies, and I discuss it in my 2012 post, but there are reasonable (though untested) explanations for it. Some butterflies, for instance, have mimicry limited to females, with females of a single species varying in appearance across their range to mimic the local distasteful species (“Batesian mimicry“), but males look the same everywhere. That’s usually explained by sexual selection: females have a hardwired search image for males of their species, and while the females may change appearance based on local selection pressures to resemble distasteful “model” species, the males are prevented from doing so because they’d lose more in sexual attractiveness than they’d gain in protection from predation.

That 2012 article appeared in the Guardian (the report has disappeared) but there were no scientific papers describing it. Now, after seven years, one has finally showed up, in the Czech journal Acta Entomologica Musei Nationalis Pragae. Click on the screenshot below to see it and get a free pdf; the reference is at the bottom.

There are actually two species mentioned in this paper: Formiscurra atlas, found in Ethiopia, which was wrongly named in the Guardian report as Formiscurra indicus.  (The latter species, from India, had already been named in 2011.)  In the present paper, published in January of this year, the author (who co-wrote the 2011 paper) formally describes and names Formiscurra atlas, goes into great detail about its unusual morphology, and mention, though not in detail, the fact that in this species only the males are mimics—mimics of ants, or “myrmecomorphs”.

We can ignore the morphological details save that the species, in one sex only, is a mimic.  Here are pictures of a male and female. Fig 1 and 2 show the male, side and dorsal (top) view, respectively, while 3 and 4 show the female. The male has a round protuberance on its head (see the eyes behind it) that makes it look more antlike. The curious thing to me is that, according to the authors, they say that this ball-shaped protuberance evolved to resemble an ant’s abdomen, while to me, and in the pictures of its relative below, it looks like an ant’s head, while the male planthopper’s abdomen has evolved to resemble an ant’s abdomen. I’m not sure whether this is a mistake, but it’s at least clear that one sex but not the other has evolved to resemble an ant.

In Figs. 3 and 4 you see the female of the species, pretty “normal” for a planthopper. She does have a small cylindrical protuberance on her head that may be a vestigial remnant of the larger protuberance in males.

The authors, however, don’t say how they know that these are two sexes of the same species. DNA would tell, but no molecular analyses are described.

 

The authors also provide a photograph of a live specimen of the relative F. indicus, which is remarkably antlike, though I still say that in the first picture below (from the paper), as well as the second (from Wikipedia), the head protuberance is “supposed” to resemble the head rather than the abdomen of the ant:

From Wikipedia’s article on F. indicus. “Male climbing a twig.”

There remains only one thing to consider: why are only the males ant mimics? We know the benefits of ant mimicry, which I described in my earlier post:

Why mimic ants?  Ant mimicry is common in many diverse groups; in fact, Wikipedia has an article on it.  There could be several explanations for why the planthopper is such a mimic.  The mimicry could be aposematic, that is, the ants that are being mimicked are poisonous and distasteful, and predators have learned to avoid them.  By mistaking the leafhopper for an ant, the hoppers gain respite from being eaten, an obvious selective advantage.  Alternatively, the leafhopper could live in an ant colony and gain advantages that way, including protection by being in a group or getting access to the ants’ food. I find this less plausible since ants are good at sniffing out intruders.  And there are undoubtedly other possible reasons for mimicry.

I still think that the advantage of mimicry here is “Batesian”: that is, many ants are distasteful to predators like birds and lizards, as ants are full of poisons and other distasteful or toxic compounds, and very few species have them as a steady diet. If you’ve learned to avoid an ant, then a reproductive advantage accrues to any planthopper (planthoppers are tasty because they feed on sap and vegetation) that looks more like an avoided ant species. And there’s no evidence that these planthoppers are associated with ant colonies.

But on to the burning question: why is mimicry limited to one sex? If the mimics were females and the males were non-mimetic, we might explain it as we do in butterflies: males are constrained not to evolve because females retain the ancestral preference for how a mate “should” look. But in this case the mimics are the males and the females presumably didn’t evolve that much.  I don’t even want to speculate here (nor does author Gnezdilov), except to say that I’d like better evidence that these are indeed two sexes of the same species. Maybe I’ve missed earlier data on that.

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Gnezdilov, V. M. 2019. A new species of the myrmecomorphic planthopper genus Formiscurra (Fulgoroidea: Caliscelidae) from Ethiopia. Acta Entomologica Museu Nationalis Pragae. 59(1): DOI: https://doi.org/10.2478/aemnp-2019-0002  Published online:  24 Jan 2020