non-limacologists) renders the slug female, as penises don’t regenerate.
Go, Santa Cruz!
Being female is more resource-demanding than being male, what with having to nourish and support eggs. Most animals have no choice but to accept their assigned role. Flatworms, however, take a proactive approach to avoiding motherhood by trying to stab the other with their penis in an act called “penis fencing.” When two potential mates meet, they rear up, which makes room for them to strike with their two-headed penis on the offense, but defensively leaves their body vulnerable. Penis fencing can last an hour, with the flatworms being stabbed multiple times, until one manages to deposit sperm into the other. The victor swims away, his paternal duties complete. The losing flatworm begins to search for the extra food required for making eggs. Flatworms practice “traumatic insemination” and they are not the only ones. Bedbugs, thorny-headed worms, microscopic roundworms, wheel animalcules, fruit flies, sea slugs, and spiders in the genus Harpactea also prefer to go through their mate’s abdomen rather than through their genital tract.
Firm Handshake
The argonaut, or paper nautilus, is a small octopus found in the open ocean. Argonauts are one of the most sexually dimorphic octopodes, meaning the females are considerably larger than the males, about eight times larger and six hundred times heavier. The females secrete a thin, white, brittle shell, which had been thought for centuries to be for egg storage. More recently, argonauts have been observed using their shells to trap air from the surface so they will be neutrally buoyant at their preferred depth. Like many octopodes, the male argonaut’s third left arm develops into a hectocotylus, the cephalopod version of a penis, which the male can detach for copulation. What makes the argonaut’s hectocotylus different is that, once detached, it can swim over to the female on its own, where it attaches itself inside her pallial cavity (octopus vagina). One mark in the “pro” column for this approach is that the male argonaut can pass on his genetic information while staying a safe distance from the larger female so that he does not become part of her egg-nourishing meal plan. The hectocotylus regenerates, so he who mates and runs away may live to mate another day.
Gender Roles
Males typically benefit from mating as much as possible, in part because they can, while the females, who actually raise the offspring, have to be choosy about their partners. In a cave in Brazil lives a species of tiny louse who did not get the memo. For Neotrogla curvata, females seek out multiple mates and the males are the choosier sex. Also, the female has a penis, and the male has the equivalent of a vagina, so they did not get that memo, either. There are four species of tiny three-millimeter Neotrogla, and the females all have penises.
During mating sessions that can last for two to three nonstop days, the female penetrates the male and uses her genitals to collect sperm rather than deliver it. The female’s erect, curved protrusion is called a gynosome. During sex, the male still ejaculates, but inside his own body instead of hers. When the female penetrates the male, he delivers sperm into a duct in her gynosome, which leads to a storage organ. Because Neotrogla sex is a marathon, the mating pair have to anchor themselves. The female inflates the base of her gynosome, which is covered with tiny spines, inside the male, and it’s impossible to separate a mating pair without killing the male.
The multi-national team that discovered the Neotrogla won the Ig Nobel Prize for biology in 2017 for their paper, Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect.
Who Runs the World?
Shaking up traditional gender roles isn’t exclusive to insects but can also be seen in the committee-assembled critter that is the spotted hyena. Unlike with most mammals, the top tier of the social order is held by females, by dint of being significantly more muscular and aggressive than the males. Males rank below all the females and even the cubs. Their social standing can only change if a male above them dies or if another male joins their pack, as the newbie is automatically assigned the lowest rank, but they can never rise above the females. Female spotted hyenas are so masculine that they develop a pseudo-penis, complete with false testicles and scrotum, which makes them notoriously difficult for researchers to sex, even when the animal is tranquilized. This unique genital transformation comes from a prenatal infusion of androgen, a male sex hormone. Not every female gets the same hormone boost, though.
Researchers in Kenya who studied the spotted hyena for nearly two decades discovered that high-ranking females give their fetal pups higher levels of androgen in the final stages of pregnancy than lower-ranking females do. This means that the mother’s rank in the pack could directly affect her offspring’s physical traits beyond what her genes do. In packs of forty or more individuals who scavenge to survive, aggressiveness and muscle mass are good traits to have. The extra androgen helps increases the likelihood that the genes of a more aggressive female will survive. It comes at a cost, though. The androgen that the fetal females receive damages their ovaries, making it more difficult to conceive when they are mature. The androgen is also what causes the female spotted hyena’s genitals to change, a lot. The clitoris elongates to protrude anywhere from seven to twenty-three inches (or eighteen to fifty-eight centimeters) from her body, hanging down from her belly like a male penis. The only visual difference between the pseudo-penis and an actual penis is the shape of the tip—blunt on females and pointed on males. This pseudo-penis can become erect and female hyenas even urinate through them. The spotted hyena clitoris isn’t the same as the clitoris of a human; theirs also contains the birth canal.
Mating is a complex cluster of social protocol and acrobatics. Sex can only happen if the female retracts her pseudo-penis, meaning there is no way for a male to forcefully copulate, even if he somehow managed to physically overcome the female. In what is likely nature’s way of encouraging genetic diversity, female spotted hyenas almost exclusively choose males who have joined their pack from another pack. Her estrus, or “heat,” only lasts about three days, though female spotted hyenas show no outward signs, at least as far as human researchers can tell.
The female spotted hyena chooses her mate, then leads or chases the smaller male to a secluded spot. She needs safety more than privacy. Research on captive hyenas at the University of California, Berkeley, has shown that the glans of the male’s penis swells in the female’s reproductive tract after the male ejaculates, causing a “copulatory lock,” as happens with domestic dogs. This leaves the mating couple vulnerable to larger predators like lions, so, as in real estate, spotted hyena mating is all about location, location, location.
The female spotted hyena then stands still and lowers her head, her way of saying, “I promise I won’t bite you, for a few minutes…probably.” Cooperation only goes so far; the male still has the comparatively tricky task of getting his penis into the opening of the female’s retracted pseudo-penis. Careful positioning is required for the male to crouch behind her and, with a bit of hopping, somehow get his penis to point up and backward to enter her clitoris. It takes time and practice to get it right, and the inexperienced male can try the female’s patience.
As hard as mating might be for the male spotted hyena, the real difficulty comes four months later for the female. She must delivery her cubs, usually two or three in a litter, through her pseudo-penis. The birth canal is only about an inch in diameter and squeezing a two-pound cub through this narrow opening can result in significant tearing. It’s not uncommon for cubs to become trapped and die, tearing or no tearing. This often leads to the mother’s death as well. Between bleeding, infection, and the complications of trapped cubs, maternal mortality rates in spotted hyenas hover around 60 percent. For those who survive, things get a little easier as the resulting scar will actually stretch more than the surrounding tissue during the next delivery.
