So, a recent science headline caught my attention. Scientists accidentally create a new species? How did that happen?
It turned out they were trying to get female sturgeons to lay eggs without the presence of a male, a phenomenon variously called parthenogenesis and gynogenesis (gynogenesis means sperm is present to activate the egg but no genetic material passes on from the male, while parthenogenesis is reproduction without male involvement at all). In order to induce this, they used sperm from a very unrelated species, the American paddlefish, on the assumption that the two species could not hybridize.
They were, uh, wrong. (Don’t worry, the fish will be well taken care of).
But Isn’t Sex Vital For Reproduction?
Myths and legends of virgin birth aside, there is no historical record of natural parthenogenesis in humans or, for that matter, in any mammals. (Also, if this really could happen, because of mammalian sex determination, the offspring would be entirely female).
Because of this we are forgiven for thinking that sex is always, every time, needed for the reproduction of any kind of larger creature.
Parthenogenesis in mammals has been managed in the lab, but it’s very, very hard. Although eggs can be activated, they never last past a few days. Mammals actually have a mechanism to prevent parthenogenesis.
However, parthenogenesis is a legitimate reproductive strategy in quite a few species, including velvet worms, flatworms, some species of snail, many insects, and a few vertebrates.
Those Lesbian Lizards
One of the most famous examples of parthenogenesis is whiptail lizards. While some whiptail lizard species have males, many are entirely female.
How the heck did this happen? It appears to have happened because sexual whiptails aren’t particularly fussed about the exact species of their mates.
The hybrid males died. The hybrid females survived, but had extra chromosomes, and this allows them to keep reproducing through the generations without sex or, well, being an entire species of clones. (They literally have four sets of chromosomes, allowing them to recombine their own chromosomes in different ways).
Whiptails still need sexual stimulation to ovulate. With no males…they have to be gay. It’s not really being a lesbian if there aren’t any boys around, but…
It’s not as robust as sexual reproduction, but it works. And even if the all-girl whiptails die out? Scientists have recreated new lines of them in the lab, so it’s likely to happen in the wild.
For most reptiles, sex is still the way to go. But more than 80 groups of amphibians, reptiles, and fish engage in situational parthenogenesis.
If there are no males around, the females will reproduce on their own. This has caused complications for zoos!
In these species, because of the way they determine sex, parthenogenesis can produce both male and female offspring.
Let’s quickly aside into sex determination for a moment. In mammals, females are homogametic (XX) and males heterogametic (XY). In some insects, this is reversed. Butterflies and moths come to mind. Some insects only have one sex chromosome. Males have one sex chromosome, females have two. (Could it be that there was a male sex chromosome but it got lost somewhere).
Birds also have heterogametic females and homogametic males.
So, if you have heterogametic females, then parthenogenesis can give you both male and female offspring, bringing back sex in the next generation. Komodo dragon females who reproduce parthenogenetically produce females (ZW), males (ZZ) and, unfortunately, some WW offspring which either don’t survive or grow into infertile females.
In this case parthenogenesis is a backup system to allow a species to get through bottlenecks, albeit with a significant loss in diversity. On the other hand, if all human males died then we would have a problem. Not so much now, because there are sperm banks, but at any point in the past.
So, there’s another famous species that engages in a form of gynogenesis.
Honeybees are very interesting critters and we know a lot about them because they have been domesticated for a long time and studied heavily.
So, here’s how bee reproduction works:
The queen does a mating flight when she is young. During that flight she will mate with as many drones as she can. (There’s no winner in a bee mating flight, although there might be losers).
Then she settles down in the colony, loses her wings and uses that collected sperm for the rest of her life. The drones fly back to their own colonies — bee drones exist as a way to trade genetic material between colonies. We used to think they died after the flight, we now know that drones live through the summer then are abandoned in the fall, with the queen producing a new batch each spring.
Bee drones aren’t like other bees.
The queen uses all of that sperm to make workers. Workers are the bulk of bees in the colony, and are considered infertile females by biologists (I’d argue they’re a different gender altogether).
To make drones?
Drones are entirely her. Drones are how she gets her genetic material into other colonies. Eggs that produce drones are not fertilized.
It’s a system that almost makes more sense if you think of colonies as separate individuals and mating flights as how colonies have sex.
The next queen? She’s created by special treatment of worker eggs. One has to wonder if queen bees don’t have some mechanism to track which sperm produces the very best workers…
So, there you have it. A few examples of nature’s “virgin births.” Makes us mammals seem a bit limited in our reproductive tactics, doesn’t it. Of course, maybe one day we’ll have other options, such as reproductive cloning or creating children that are the biological offspring of two women, two men, or even multiple people.
If any of that actually works. For right now, we might not technically need a man any more, but we’re still going to need sperm. Because mammals.