Oddly, the Guardian has published an account of a new insect species by Quentin Wheeler, a systematist at Arizona State University and director of the International Institute for Species Exploration. (He has also proposed a new species concept, but the less said about that the better.)
His article, however, is intriguing, for it describes a planthopper (an insect in the order Hemiptera, superfamily Fulgoroidea; also called “leafhoppers”) that apparently mimics an ant. As Wheeler says of the Fulgoroidea:
. . . [it is] a worldwide group of true bugs [JAC: remember, only the Hemiptera are “true bugs” to an entomologist] with about 12,000 species. That is, by the way, more than twice as many species as all mammals combined. To say that planthoppers are diverse is putting it mildly. They range in size from less than 2mm to over 100mm, populations exist with both flighted and flightless morphs, many are camouflaged green while others are brilliantly coloured including reds, blues, and hot pinks. And some, like F. indicus, are ridiculously shaped.
The new species is Formiscurra indicus, found (as the name indicates) in India; this specimen was collected near Bangalore and described by Vladimir Gnezdilov of the Russian Academy of Sciences and Chandrashekharaswamy A. Viraktamath of the University of Agricultural Sciences in Bangalore. The intriguing thing is the sexual dimorphism, with the males looking antlike (I don’t have a picture of the female):
As Wheeler notes:
Sexual dimorphism is nothing new in the tribe Caliscelini, to which the new species belongs. In fact, males and females of two species of the genus Gelastissus look so different that they were initially described in separate genera! Females of the new species have reduced wings, a very compact body form, and the front of the head elongated into a cylindrical process. But the male is something else entirely.
Even as an entomologist I had to do a double take when I first looked at the photograph of F. indicus to be sure I knew which end was which. Males of the species apparently mimic ants, although it can be debated whether the ants should be flattered. The abdomen is exceedingly shortened and bulbous and the main part of the cranium almost looks as if it is part of the thorax, which has impressively long legs, but these modifications pale in comparison to an elongate protrusion on the front of the head that is approximately the size of the abdomen and similarly bulbous. Weird.
There are two questions that Wheeler raises implicitly but doesn’t address:
1. 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.
2. Why are only the males and not the females mimetic? This is tougher; one would think at first blush that males and females would be subject to similar selective pressures. But that’s not necessarily true. In swallowtail butterflies of the species Papilio dardanus, for example, males retain the ancestral wing pattern, which is similar among populations, but females diverge, with females from different places mimicking different unpalatable models. P. dardanus is palatable—to birds. In the picture below, we see different “races” of P. dandanus from different places in Africa mimicking different local model species, all of the models unpalatable (the P. dardanus female mimics are in columns at left and right, while the local models are in the center).
The males in all populations look pretty much the same: like the male at upper left. (A female at upper right is the presumed “ancestral” form, which occurs—and looks like the males— in areas where there are no unpalatable models.) But note that the females are free to vary among populations—a remarkable case of inter-population differences within a species. Why do the females but not the males vary, responding to local selective pressures?
One explanation involves sexual selection, and I’ll leave you to ponder that and make suggestions below?
By the way, which end of the hopper above is the head?
h/t: Matthew Cobb