A new forcepfly—and a disquisition on insect genitals

“Our faculties are more fitted to recognize the wonderful structure of a beetle than a Universe.”

—Charles Darwin, Notebooks

From Eurekalert we have the description of a new species in a group I didn’t know existed (reference and link to open-access paper below): the forcepflies.  Austromerope braziliensis is the newest species described in the family Meropeidae, one of the smallest insect families (it’s in the small order Mecoptera). In contrast, the family Chrysomelidae, or leaf beetles, contains 35,000 species.

The family Meropeidae held only two species until A. braziliensis was just described (from Brazil, of course).

Wikipedia describes this small and enigmatic family:

The Meropeidae are a tiny family of the order Mecoptera with only three living species, commonly referred to as “earwigflies” (or sometimes “forcepflies”). They are: the North American Merope tuber, and the Western Australian Austromerope poultoni, and the newly-discovered South American Austromerope brasiliensis. The biology of these species is essentially unknown, and their larvae have never been seen. The disjunct distribution suggests a common origin before the breakup of the ancient supercontinent of Pangaea.

They’re called “earwigflies” because their “forceps” resemble the pincers of earwigs, an unrelated group in the order Dermaptera. Earwig pincers (below) are used to capture prey and defend themselves. Their name comes because they were erroneously thought to enter human ears and then drill into the brains with the pincers:

The new paper in ZooKeys by Machado et al.  shows A. braziliensis with enormous “pincers,” which in this group aren’t defense organs but genital claspers, presumably found only in males (the paper describes only one specimen, and I haven’t found much about the females in this group):

 Many insects have bizarre genital structures in males that presumably help secure or grasp the female, and probably arose via sexual selection. (For a great scientific book on this topic, read William Eberhard’s book Sexual Selection and Animal Genitalia.) In fact, when two insect species are very closely related, the character most likely to distinguish them is the shape and size of the male genital structures. (This is true in many groups besides insects, by the way). In contrast, the genitalia of females from related species are often nearly identical. Those two facts (I’d call them “Coyne’s Rule”, except there’s already a “Coyne’s Rule” in biology) imply that sexual selection on males is one of the most common evolutionary processes.

How does that selection work? The ability to reproduce is, of course, the sine qua non of natural selection, so one would expect strong selection on those traits connected most directly with reproduction. Any male who is better able to grab and hold onto a female with his genitals will have a reproductive advantage over other males, and this could lead to the elaboration of male genitals. There are other explanations, too, including the suggestion that the bizarre shape of some male genital structures, which don’t seem to help them hold on, somehow stimulate the female’s “tactile preference”, inducing her to mate. (This is called the “sensory bias” hypothesis.) There are other explanations, too, which you can read about in Eberhard’s book. The forcepfly pincers, however, are likely to be adaptations for grasping females, though we don’t know for sure.

Here are the male pincers in closeup:

Eurekalert gives more on the new paper:

A new species of forcepfly Meropeidae (Mecoptera) from Brazil was described, representing only the 3rd extant species described in this family and the 1st record of the family from the Neotropical region. The distribution and biogeography of the family are discussed and it is even proposed that Meropeidae originated before continental drift and then divided into two branches, northern and southern, with the breakup of the old supercontinent Pangea. The study was published in the open access journal ZooKeys.

Despite all previous collecting efforts in this area the species had never been recorded before. The specimen was collected in a private ranch near a forest fragment surrounded by farms in the Atlantic Forest biome, one of the most threatened in Brazil. It can be found in a variety of habitats, including woodland, Jarrah forest, and sand plain vegetation. What makes forcepflies special is the fact that little is known about their biology and the immature stages remain a mystery to scientists. The adults, who are nocturnal and seem to live on the ground, are also capable of stridulation, or the production of sound by rubbing certain body parts.

“The discovery of this new relict species is an important signal to reinforce the conservation of Brazilian Atlantic Forest biome. Certainly there are many more mecopterans species yet to be discovered in these forests”, said the lead author Dr Renato Machado from the Texas A & M University, College Station, USA.

Here’s the beast’s head, missing one antenna:

And the lovely antenna, which resembles a stalk of wheat:

Just for fun, here’s a figure from Eberhard’s book showing a unique and nefarious structure in male damselflies: the “penis scoop.” Female damselflies often mate with several males, and when a male tries to copulate with an already-inseminated female, he uses special structures on his genitals to scoop out the sperm from the previous males before ejaculating his own! That’s of obvious reproductive advantage to males, and instantiates the old adage “evolution is cleverer than you are.” But it’s also of interest that males from different but closely related species have differently-shaped scoops.

One would have thought that there is only one optimal design for a penis scoop, but there are obviously other factors in play here. Different tactile preferences of the females may apply, as well as the possibility that the internal sperm-storage organs of females from different species may have evolved by “antagonistic sexual selection” to counteract the male’s attempts to remove the sperm she carries. And the way a female evolves to counteract the males’ penis scoops may differ in different species.

The recurved spines are used to collect the sperm of previous males and remove them, much like a fishhook:

h/t: A tweet from Ed Yong via Matthew Cobb

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Machado, R. J. P., R. Kawada, and J. A. Rafael (2013) New continental record and new species of Austromerope (Mecoptera, Meropeidae) from Brazil. ZooKeys 269: 1–10. doi: 10.3897/zookeys.269.4255

(Note: the link given at the Eurekalert page is wrong.)