Ready for another science post? The laws of physics deemed that today there would be two.
A new paper in the Journal of Orthoptera Research by Sigfrid Ingrisch et al. (free link if you join Researchgate [also free]; reference below) describes two recently-discovered and newly-described katydids from Sabah (part of Malaysia on the northern part of Borneo). I’m busy today and can’t write about this at length (and, in truth, you don’t need to know more than what I’m putting down here), but have a look at the abstract, which notes the vein-like structures that curve backwards on the “tegmen” (forewing), making them resemble the veins of leaves. In one species the females are reddish-pink, like young leaves, while males are green—a remarkable case of sexual dimorphism. (The males of the other species haven’t been found yet.) These are clearly leaf mimics, though there’s an issue with coloration (see below). Here’s the paper’s abstract, which I’ve tried to clarify a bit by defining technical terms):
Two new species of the previously monotypic genus Eulophophyllum Hebard, 1922 are described. All species of the genus known up until now occur in forested areas in Sabah, Borneo. The genus is unique for the strongly widened media field of the tegmen [JAC: hardened forewing], in which all branches of the media anterior plus radius sector are strongly curved and run anteriorally. There is also a striking color difference between the sexes, with males uniformly green and females pink. The two new species E. lobulatum Ingrisch & Riede sp. n. and E. kirki Ingrisch & Riede sp. n. have large leaf-like expansions of the hind tibiae that are absent in E. thaumasium Hebard, 1922. They differ from each other in the number of main vein branches in the media field of the tegmen. Stridulation [JAC: “chirps”, as in crickets, made by rubbing the wings together; the species have a special “file” on one wing that produces the sound] of E. lobulatum sp. n. consists of short double-clicks ranging from 6.5 to 8.5 kHz, repeated at longer intervals.
Here’s a pinned specimen in which you can see the stridulatory “file” apparatus (“D”) and the leaflike expansion of the upper part (tibia) of the hind legs, making them look even more cryptic:
Possible reasons for the pink coloration of the females are as follows: (1) Against a background of variable vegetation a pink female with green veins might merge optically with the background when seen from a distance (Fig. 3G); (2) It is possible that the pink individuals which have so far been found may have simply been resting on an atypical background – making them more obvious to human observers. Their ‘usual’ resting site may be reddish first-flush leaves, common in many rainforest plants; (3) the pink coloration might serve as warning coloration, although we consider this to be unlikely. Further field observations will be necessary to shed light on the function of the pink coloration of these species and it may reveal something unexpected.
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Ingrisch, S., K. Riede, and G. Beccaloni. 2016 The pink katydids of Sabah (Orthoptera: Tettigoniidae: Phaneropterinae: Eulophophyllum with Description of two new species. Journal of Orthoptera Research25:67-74.
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… I can’t help but wonder if “stridulation” has the same etymology as “strident” – anyways it’s a great word to learn. The female is mimicking a leaf that looks like a common plant – maybe that’s why I think it’s amazing.
Could it be a matter of size? If the females are smaller than the males, then they’ll want to hide among smaller (hence younger) leaves.
That’s fascinating. The authors speculated that the pink coloration may serve as a warning. Is there any reason why one gender of a given species might use aposematic coloration as a defense mechanism, but not the other gender?
Perhaps the difference has to do with where females lay eggs and their vulnerability while doing so? Also, I imagine that younger pink leaves would be less appetizing to herbivores than older green ones. They may not only be hiding from predators, but grazers as well. How embarrassing for a species (if a species could collectively blush) to avoid getting eaten by a predator only to end up in the stomach of a leaf eater! The males and their less-valuable gametes might be not only more mobile, but also suffer a lower cost by being mistaken for a tasty leaf.
As for why they might also be found among green leaves, I imagine that young leaves are also found among older green leaves, at least in overlapping branches, making the presence of a bright pink katydid on a green leaf less obvious to a predator familiar with the plant.
“Also, I imagine that younger pink leaves would be less appetizing to herbivores than older green ones.”
I think in general it is the opposite way round – young leaves tend to be more palatable and easily digested. Although defensive chemicals such as tannins may be present in the developing leaf they are diluted by the higher moisture content also higher nitrogen content of the growing leaf may make it more nutritionally valuable to a herbivore.
> 6,000 species of katydid worldwide – I wonder how many species in the Sabah forests? How did the researchers determine the pink & green specimens are of the same species? By observing courtship? If courtship, could the female & male be closely related, but different species & the female had her dance card marked wrongly? 🙂
Could anyone tell me if the likliest predators have color vision? They may just appear as the same shade of grey if they don’t.
Here’s some general info I’ve just collated – can’t guarantee it’s 100% correct, but it’s my impression now that the katydid of the sabah forest is under great pressure to mimic!
Birds: colour vision orientated since they are tetrachromatic [four types of cone cells inc UV vision] which knocks us poor primates into a cocked hat. Our colour vision is useless at night, but it seems that other creatures can see some parts of the colour spectrum in low light
[Primate] Tarsier: Nocturnal animal with trichromatic vision adapted to low light
Carnivorous bats: They are nocturnal & have dichromatic red & blue colour vision [& UV too I do believe] – it is reasonable to suppose they see colour at night
Tree shrew: not a true shrew. Closely related to primates. Diurnal? Dichromatic
[Primate] Slow Loris: Nocturnal with very acute monochromatic vision
Reptiles [lizards etc.]: They generally have good trichromatic colour vision, but that’s all I know. Plenty of species prey on insects & no doubt that holds for the Sabah forest too
Insects: I don’t know what preys on katydids so I can’t look this up
Damn but those katydids need all the camo they can get!
thanks!
I had the same thought initially, but then I figured birds were the most likely predators.
Well, that is pretty damn awesome! Ok, let the speculations come out.
1. It would be nice if the females at times preferred to rest at younger leaves, where they not only would blend in when seen up close but they would also be amongst the more nutritional leaves. New leaves are packed with nutrients, and lady katydids need to pack on the grams to make lots of eggs.
2. I suppose any preferences in resting sites would be best looked for in the day, when they are most visible. If seen at night, they could be anywhere.
3. Just a point so that everything seems more pointy: pink coloration is rather common among katydids and related tree crickets. Even here in the midwest I see green and pink ones. I have no idea if there is a sex bias in this.
I found this online re pink & green in a particular katydid species: “Recent breeding experiments have revealed that bright pink, not green, could be the most genetically dominant colouring of the North American oblong-winged katydid”
https://blogs.scientificamerican.com/running-ponies/in-north-american-katydids-green-isne28099t-the-dominant-colour-pink-is/
Yes, I saw something like that too. Anyway, it suggests that ‘going pink’ is a trait that is ready to be used in these sorts of critters, in case natural selection calls for it.
Something tells me Becker & Fagen would get a kick outta re-issuing Steely Dan’s “Katy Lied” album with a picture of this species of Eulophophylluma substituted for the original, generic katydid on the cover. It’d add a whole nother level of jouissance to the irony of the title.
Excellent Steely Dan reference.
I like the science posts. Can’t always comment! 🙂
Reblogged this on The Logical Place.
My uninformed hypothesis:
Females are smaller, thereby resembling younger leaves. If the mating season takes place while the leaves are young, there would be no need for the females to then become green because they have already reproduced… but then why are the males green?
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I LOVE EVOLUTION!
Remarkable mimicry. I am at a loss to explain the dimorphism beyond the ideas already stated. If it were the males that were brightly colored, I would suspect sexual selection.
My guess would be that assuming calling males are likely to attract predators, only when females are looking for a mate would they want to be in the vicinity of males.
Once that is achieved they can sit away from the noisy males on different foliage quietly feeding and laying eggs.
I want to add that this is just a guess, I have very little working knowledge of Katydids…
DAMN! and I thought my local katydids, Pterophylla camellifolia were leaf-mimicking badasses! I am impressed. I won’t even bother attempting one of my half-assed armchair biologist hypotheses. I’ll just say Wow.
As a psychologist, I love the possibility that the reason for the predominance of females on “wrong-coloured” leaves reflects the perceptual bias/capabilities of the human observers: all the (presumably majority) females on the “correct-coloured” leaves, of course, being invisible to the human observers. Great fun!
There would be to my mind no problem for sexual selection to explain the difference. It is a well known that sexual selection does drive some pretty exaggerated morphology… i see this as no different.
But all said and done, not enough is known about these creatures.
Cool.
Are females actually smaller? If so why? Males use stridulation, or do they fight too? Some good speculations above. I like the idea that after copulation the females want to put some distance between themselves and those very noisy males (if males are indeed noisier than females).
Fascinating post.
Mimicry is so cool.
🐜
The differential hiding hypothesis strikes me as most plausible. As to why males and females should habitually rest in different places, a possible explanation is that the males’ choice is determined by the best place from which to stridulate and perhaps large flat mature leaves offer some advantages (e.g. acoustically) in this respect, whilst females rest amongst the younger leaves where they have access to better food resources (as Mark S points out above, they need plenty of nutrients in order to develop the egg mass) and venture away from this only temporarily in order to mate. It would be interesting to know if males compete for ‘singing platforms’.
It will be nice if someone is able to do the field observations and or lab experiments to tease out the reasons behind this dimorphism but even if this doesn’t happen this remains a fabulous example of mimicry/camouflage. Thank you for bringing it to our attention!
If being cryptic or a mimic is so good, why isn’t every insect? It looks like being such an awkward shape makes it hard to escape…?
Isn’t that a question you could apply to any adaptive trait? For example, if flying is so brilliant why doesn’t everything fly?
As phrased, your question supplies one answer straight away – crypsis and mimicry are not the same thing and if you are mimicing a something that has warning coloration – like a hornet – then the effectiveness of your colouring (and that of your model) depends on it being conspicuous and easily perceived and understood by potential predators. That’s incompatible with being cryptic*.
Clearly there are various potential solutions to many evolutionary problems (such as avoiding being eaten) and which solution a species ends up with will depend on chance (which mutations actually happen with the gene pool) and on various constraints including other aspects of its ecology, the genetic material you have to work with and so on. Furthermore, as in the cryptic versus mimic example, some solutions may then preclude others – e.g. it is quite conceivable that an animal could be heavily armoured and well camouflaged but less likely that an animal could be heavily armoured and ultra fleet-footed.
*It should be mentioned, though, that there are quite a few insects – including many grasshoppers – that rely on crypsis but which also have brightly coloured wings (or other body parts) that are kept hidden up to the point at which the insect is detected/stumbled upon, when they are suddenly revealed. This has the effect of startling the predator and giving the insect an opportunity to escape. In the case of grasshoppers it also has the effect (at least to human observers) of making it very difficult to relocate the insect after it has flown off even if you have watched it land. The sudden switch back from being conspicuous to cryptic seems to enhance the crypsis!
Why should this katydid be sexually dimorphic? Knowing a little katydid natural history (ecology) helps. I just did some googling and found out that herbivorous katydids often specialized to feeding on one or a few host plants and tend to stay near them. In fact, katydids are known to hide away in favored shelters to which they return each day after feeding. Some katydids have territorial males that drive away rival males, so that only one male is present on a host plant. The katydids described here live in high-diversity tropical forests of Borneo, and probably concentrate around rare, scattered food plants.
Dimorphism (and polymorphism) in protective coloration may be adaptive and evolve because predation is frequency dependent: predators tend to pass over prey with which they have less experience. This idea dates from E. B. Poulton in the late 19th century, but it was R. A. Fisher who worked out the mathematics (with regard to polymorphism in mimetic butterflies) in the 1920s. When a bird finds a big, juicy katydid, it will tend to look for others with the same appearance. With dimorphism, individuals of the sex opposite that of the prey item would tend to be overlooked relative to situations in which the sexes look alike.
I suspect that the host plant(s) has leaves that are red when young. This is a trait shared by many plants that grow the tropical forest undergrowth. A pink leaf-mimicking female could live and feed relatively securely on a plant that sprouts throughout the year, i.e., in the wet tropics. The male would be relatively protected no matter what, but perhaps less when it fed on tender red leaves. Suggestive stuff.
I have no idea what is going on here, but I do wonder, having just reskimmed _Endless Forms Most Beautiful_ for a project: how *developmentally* does this work out? Could one throw a gene switch and see what happens if one sex is made with the wrong colour?
That’s amazing. They’re beautiful.