Ok, So these creatures don’t literally mate with themselves and are not that ugly but they are capable of reproducing asexually. Humans don’t hold the monopoly on immaculate conception. At least some other species have long counted on it to keep their gene line going. The biological mechanics are different for every one of them, and while none of the techniques sounds like much fun, they at least don’t lead to awkward conversations if the relationship doesn’t work out.
Male seahorses are the ones that get pregnant, carrying the developing young in a pouch on their front. There isn’t much romance in any of this, but as with so much in the natural world, what’s lost in poetry is more than amply made up in imagination.
In 2003, biologists reported that a female crayfish, living by herself in an aquarium, repeatedly laid eggs that developed into offspring.
The explanation is a process called apomitotic parthenogenesis, which involves skipping a step in early egg development. Instead of dividing so that they carry half the required number of chromosomes—with the missing ones supplied by the sperm—these crayfishes’ eggs stay whole and develop into little Marmokrebs directly.
Later research suggests that the marmorkrebs is an asexually reproducing form of the crayfish Procambarus fallax, which handles its baby-making in the ordinary way. How and why the asexually reproducing form arose is still a mystery. What’s certain is that with the critter now popular among aquarium owners worldwide, it pays to have plenty of scuttling room in your tank. Even if you buy just one marmokrebs, you’ll wind up with more.
In 2006, a female dragon named Flora, which lived in a zoo and had never been exposed to male dragons, laid a clutch of eggs that hatched normally.
In Komodos, the process seems to start with eggs that are like any other, with half the number of required chromosomes. But at some point in the development process, the chromosome count doubles back up and a Komodo embryo results. Only males can result from this process. That’s because in Komodo dragons, females are the ones that have two different sex chromosomes—in this case a Z and a W. Males are ZZ. When the chromosomes in an egg divide and then multiply themselves by two, they can thus produce only a non-viable WW or a viable ZZ—a male. The implication—and perhaps the very reason for this arrangement—is that it would allow a female Komodo to swim to an isolated island and produce her own sexually reproducing population, using her sons as mates once they reached maturity. Nobody said nature was always pretty.
Some species of these small southwestern lizards are all-female. They appear to be the result of cross-breeding between two other lizard species, which left them with twice the usual number of chromosomes. That fluke makes them well-suited to producing offspring all on their own, without needing a complementary male set of chromosomes to complete the picture.
The whiptails haven’t forgotten about sex totally, though. These all-lady lizards engage in pseudosexual behavior—like mounting each other—before laying their eggs. Even among go-it-alone breeders, old habits die hard.
Think it would be hard getting a date if you were a hammerhead shark—easily the homeliest fish in the seas? Imagine being a species of hammerhead called the shovelhead, which doubles down on ugly in just the way its name suggests. In 2007, researchers discovered that a female shovelhead living in captivity that had never been exposed to a male got around the lonely-on-Saturday-night problem by joining the group of species that have mastered the act of virgin birth. The shovelhead managed this feat through automictic parthenogenesis—which is different from the marmorkrebs’ apomictic—producing a full set of chromosomes in the egg by doubling the mother’s genetic material, rather than getting half from a male.
Solo reproduction gets stranger in the insect world. Among certain wasp species, fertilized eggs develop into female offspring with the regular number of chromosomes. Unfertilized ones develop into males with only half. But if the female wasp is infected with the Wolbachia bacteria, a different kind of immaculate conception results. Instead of splitting to yield eggs with half the normal number of chromosomes, these wasp eggs forgo division and keep their normal chromosomal number. They then develop into females that are clones of their mothers. The females that result, though, are unable to reproduce sexually. And soon, the entire female population is made up of infected wasps with no possibility of producing offspring that can escape the infection.
Honorable mentions in the Bizarre Breeding Sweepstakes go to the grouper, a species of fish that is female until it reaches maturity, at which point it can switch back and forth between genders. The anglerfish gets a nod too. They all seemed to be female, until researchers realized the little parasites clinging to them were actually anglerfish males. Now this one can be classified as ugly.