What I know is animal sex, is fun to write about. Without letting this blog become a home for things I write that don’t get published where they were intended, here’s the second time I’ll do that. I wrote this article for the 10th edition of Elements, the Puget Sound science magazine, but it didn’t make the cut (because there was already an article about animal sex). But here it is.
Mitigating the Investment in Intercourse
Hugh Hefner and the Pope don’t want you to know, but coitus will cost you. The process of creating gazillions of gametes or even just a couple copies of yourself is quite the resource suck. Eggs are like sack lunches for the beginning of a life form, so you better stock that cooler with all the best nutrients you’ve got. Sperm are much smaller and hold much less responsibility, but still bear the burden of beating a female’s defenses and often find strength in sheer numbers. Producing these copulation components costs the parent dearly, taxing energy use, hogging body mass, and potentially hindering locomotion. Beyond the price tag on gametes, if you are an animal that practices internal fertilization, especially live birth, gestation can continue to devour your dinners like a parasite for up to 770 days! (the extreme end of elephant gestation periods). Beyond that, nurturing a neonate to a point of independence often requires nepotism that nears altruism (though likely motivated by the personal goals of genetic perpetuation). As a result, nature has made some creative variations on our heteronormative human paradigm of the hanky panky.
Two hermaphroditic flatworms penis fencing, attempting to defend themselves from impregnation.
Platyhelminthes Penis Fencing and Personal Plan B
According to Bateman’s principle, we consider the individual burdened with the production of female gametes, which are larger and richer, to be carrying the brunt of the cost of reproduction. But what about hermaphrodite sex, where mutual impregnation is possible? Ideally, for the proliferation of the population, both individuals involved in the exchange would bear offspring, but some feisty flatworms have a different idea. Certain members of the phylum Platyhelminthes participate in what has come to be known as penis fencing. The phalli of these inventive invertebrates are reinforced with a pair of crystalline stylets that, if they can pierce the partner’s body wall, deliver sperm directly into the circulatory system. Pairs of passionate Turbellarians will tousle about in showy displays of spineless acrobatics trying to avoid status as the one that got stabbed. The losing side of this violent lovemaking leaves a flatworm injured and impregnated. Further, one particular genus of Platyhelminthes, Macrostomum sp., have developed a way to undo what’s been done by doing the dirty. These species practice more traditional transfer of gametes involving a specified female receptacle, but post-copulation, an individual can double-over and suck the sperm of an unworthy partner out of the female genital pore. However, these unwanted willies don’t go willingly; the sperm are shaped more like a harpoon than the familiar human flagellate, and come with two backwards-facing barbs at the back end that act as an anchor.
The ninja slug shoots its potential mate with 'love darts' to get them in the mood.
Battle Sex Gastropoda
The ninja slug, recently discovered in the mountains of the Malaysian section of the island of Borneo, found an unusual method of persuasion for procuring a partner that puts roofies to shame. This long-tailed slug shoots a calcium carbonate dart laced with love potion. The boinking bullet injects hormones to help get their gastropod mate in the mood. This fast-forward foreplay can be important for slugs, who generally have extremely long courtship periods which can sometimes result in the loss of a beloved limb (see apophallation in Arolimax, or just consider the only appendage a slug has to lose). The more these sneaky slugs can speed up the process, and in turn sooner resume such selfish endeavors as eating and seeking shelter, the better.
The male seahorse graciously gains the baby-weight for the reproductive pair by fertilizing and brooding the transferred female gametes in his abdomenal pouch.
Stay at Home Seahorse
Counter to the assumptions of the Bateman principle that girls give more in reproduction, seahorses have found a way to reverse the rearing investment. The father takes on the task of internally transitioning the brood from gametes to juveniles in an abdominal pouch lined with a soup of sustenance. For all intents and purposes, the male is the one that gets pregnant. Up to 1500 eggs are embedded into his pouch during copulation with a female, briefly bathed in seawater, and then closed off in a comfortable belly to be fertilized and fed. Males can carry the young for up to 45 days, receiving only 6-minute daily visits from his monogamous partner. The rest of his day is spent vacuuming food up through his furtive snout to feed his tiny flock. This method of male brooding is thought to distribute the price of reproduction more evenly between the sexes in this unfathomably faithful species.
It’s as if these smart smangers understood the setbacks of shtupping without mechanisms to mitigate the necessary resource investment, and adapted accordingly. Personally, I think the evolutionary adjustments that resulted are cooler than any form of contraception or social reform our species has yet created.