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

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.

_____________________

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

18 Comments

  1. ThyroidPlanet
    Posted July 17, 2020 at 10:09 am | Permalink

    Sub

  2. Posted July 17, 2020 at 10:21 am | Permalink

    Not a biologist but just thinking… if mating is not a mutual selection, then I presume the sex doing the selecting – needing to travel more perhaps seeking a mate – could be more successful with mimicry while the sex being selected would be more successful by not changing appearance and staying more localized.

    • revelator60
      Posted July 17, 2020 at 12:54 pm | Permalink

      That sounds like the most promising explanation to me. The male’s habits place him in greater danger of predation.

  3. Posted July 17, 2020 at 10:32 am | Permalink

    This is very surprising, if true. As you say,
    “I’d like better evidence that these are indeed two sexes of the same species.”

    It is a bad sign that the authors don’t discuss this.

    • loren russell
      Posted July 17, 2020 at 11:56 am | Permalink

      As an entomologist myself… I’m guessing that that a) the author collected a fair number of both ‘forms’ commingled on the same hosts at the same time and found that the “mimetic” individuals were all anatomically male, the non-mimetic all female. I can think of numerous cases, including the insect I did my thesis on, where marked sexual dimorphism was obvious as soon as the two sexes were observed.

      This kind of inference is common place. It has occasionally proven wrong [mostly I think, in old museum collections where there’s poor labelling and little information about ecological associations. Here, the initial diagnosis as sexual dimorphism had bee applied to the previously known F. indicus, as well. Taken together, I can see why the author [and reviewers] saw no need to explain the these two morphs as a case of sexual dimorphism in the present paper.

      • rickflick
        Posted July 17, 2020 at 12:52 pm | Permalink

        Can you venture an opinion as to how the dimorphism comes about? Morphological change in one sex?

        • loren russell
          Posted July 17, 2020 at 8:19 pm | Permalink

          NO, beyond the observation that the broad abdomen of the females in this group of planthoppers make them markedly less ant-like to begin with. And making the female abdomen more antlike would probably result in lower fecundity.

          [In my first reply above, I forgot to note that entomologists are often able to associate sexually dimorphic males and females by finding them “in copula”….

  4. Michael Coon
    Posted July 17, 2020 at 10:36 am | Permalink

    How do we know this is mimicry at all? Perhaps it’s a real male sexual characteristic and the ant mimicry is really pareidolia?

  5. GBJames
    Posted July 17, 2020 at 10:43 am | Permalink

    Sub

  6. Jonathan Wallace
    Posted July 17, 2020 at 11:05 am | Permalink

    I entirely agree that the head protuberance of the bug ‘represents’ the head of the ant. It looks very convincingly ant-like viewed that way but not if you consider the protuberance to be mimicking the ant’s abdomen.

  7. rickflick
    Posted July 17, 2020 at 11:22 am | Permalink

    Curious that the big nose should interfere with feeding. In any event, these mimics are really great. God certainly works in strange ways with his tiniest toys.

    • Posted July 17, 2020 at 5:02 pm | Permalink

      Planthoppers have a stylet,a sort of drill, to suck plant sap. It’s deployed perpendicular to the long axis of the body, straight into the plant. The big nose has no effect onthis.

  8. jezgrove
    Posted July 17, 2020 at 11:35 am | Permalink

    Here’s The Guardian‘s article – the link probably got changed in their website update: https://www.theguardian.com/science/2012/nov/11/formiscurra-indicus-new-to-nature

  9. Janet
    Posted July 17, 2020 at 12:01 pm | Permalink

    Perhaps the mimicry being restricted to males has a simple morphological explanation – the shape change in females would inhibit mating?

    • Janet
      Posted July 17, 2020 at 12:53 pm | Permalink

      What I mean is the barrier might be purely mechanical – such that the parts would no longer fit properly.

  10. Steve Pollard
    Posted July 17, 2020 at 3:40 pm | Permalink

    This non-biologist thinks that the article, and PCC(E)’s elaboration of it, are extraordinary and wonderful. Thanks so much!

  11. Posted July 17, 2020 at 5:15 pm | Permalink

    Lemme do some handwaving.

    It is quite possible that the head bulb does mimic the abdomen. I note that the plant hoppers short antennae, adjacent to the bulb, are good matches to the metathoracic spines that ants often have also near the abdomen :
    https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Aphaenogaster/i-hSZNmm6/A

    The trick would be to learn if the plant hopper walks backwards to enforce the deception. There are cases where this is done because nature is weird that way sometimes.

    It is ok I think for the male to be the mimic in this case, since plant hoppers generally find each other for sex by the male ‘singing’ (stridulating). We can’t hear them, btw, but that is how they ‘do it’.

    • Posted July 17, 2020 at 7:25 pm | Permalink

      Does the singing make the male easy for some predators to find? Maybe that is why he has to go out of his way to mimic something inedible.


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