Saturday, 19 April 2014

First female “penis” discovered in cave-dwelling insects

Neotrogla aurora female penis
Image showing the female penis of N. aurora
Credit: Current Biology, Yoshizawa et al.
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Psocoptera
Family: Prionoglarididae
Genus: Neotrogla
Species: N. aurora, N. curvet and 2 other

This Thursday, researchers announced that they have discovered several insect species that display the "world's first" known instance of gender-reversed genitalia. In simple words, they have found 4 insect species with female... "penises" and male "vaginae"!

All four species live in dry Brazilian caves and feed on bat guano. They belong to the genus Neotrogla, of the Psocoptera order which is commonly known as booklice or barklice. They are small -2.7 mm to 3.7 mm long- and look like flies, with nothing particularly strange about their appearance other than their bizarre reproductive system.

"Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent organ is also reversed." said leading author, Kazunori Yoshizawa from the Hokkaido University in Japan.

Prolonged and reversed mating
The researchers found that these insects mate for an impressive 40 to 70 hours, during which, the female inserts an elaborate, penis-like organ -called gynosome- into the male's vagina-like opening.

According to co-author Rodrigo Ferreira, the females may forcibly hold on the males for such long periods of time to get as much of their sperm and seminal fluid as possible.

"One of the couples copulated for around 73 hours." said Ferreira.

The spikes along the female penis anchors it to the male's "vagina" so strongly that when the researchers tried to separate one of the couples, they tore apart the male’s body without affecting the genital coupling.

N. curvet mating
Female N. curvet (top) mates with a male
Credit: Yoshizawa Kazunori

The researchers speculate that the prolonged copulation and the genitalia reversal may be an evolutionary trait guided by the resource-poor cave environment in which these insects live. Males provide females with nutritious seminal fluids in addition to sperm, making it advantageous for the females to mate for prolonged periods.

The findings on Neotrogla offer new opportunities to test ideas about sexual selection, conflict between the sexes, and the evolution of novelty, claim the researchers, who now plan to look into studies of behavior, physiology, and more. First on their list is to establish a healthy population of the insects in the lab.

"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborated female penis." said Yoshitaka Kamimura from Keio University in Japan. 

It has a penis, so it should be a male, no?
Contrary to what common sense may tell you, the presence or absence of certain genitalia isn't the determining factor to whether an individual is male or female. Gametes are.  

By definition,male gametes are small, motile, and optimised to transport their genetic information over a distance, while female gametes are large, non-motile and contain the nutrients necessary for the early development of the young organism.

It just happens that males usually have a penis and females a vagina. Usually..

- Yoshizawa, K., Ferreira, R., Kamimura, Y., & Lienhard, C. (2014). Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect Current Biology DOI: 10.1016/j.cub.2014.03.022

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