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Carnal Knowledge | Masculine insecurity is sensible for insects
What they risk: Infection that kills only males, or turns them into females.
By Faye Flam
Inquirer Staff Writer
If you thought feminism, political correctness and male-bashing represented a threat to manhood, well, it could be much worse.
Many other species are beleaguered by infections that can turn males into females, selectively assassinate males, or render males irrelevant by allowing females to give birth without them.
"It's a jungle in there," says Rochester University biologist Jack Werren of the warfare going on inside cells of many of our fellow creatures.
One such male-targeting agent, called Wolbachia, infects millions of species of insects, he says, which can be either feminizing or male-killing or asexuality-inducing.
"Wolbachia represents one of the biggest pandemics in the history of life," he says.
Males are a target for a reason, he says. Many types of bacteria travel from parents to offspring through eggs. Males represent a dead-end, so such infectious agents benefit by doing away with them before they're born while leaving females unharmed.
If that weren't enough, Werren says, males tend to find themselves disproportionately targeted by mutations and other "selfish" genetic anomalies.
In last week's issue of the journal Science, Werren, along with Dutch biologist Leo Beukeboom and colleagues, described a species of wasp - the jewel wasp - in which apparent genetic males appear and act just like females.
Cases like this, said Werren, could help explain why the living world uses so many diverse ways of determining who's male and who's female - our system of X and Y chromosomes representing one of dozens.
In wasps, as well as bees and ants, the system is completely different from ours. Males carry only half the genes of females. That's because they come from unfertilized eggs, so they're missing the contribution their sisters get from sperm.
What Werren and his colleagues found was that some of the wasps with a half-supply - or "haploid" - set of chromosomes, were female, not male.
Only one other case of "haploid" females was ever reported. It involved a species of mite, and it didn't go well for the males. A feminizing bacteria had apparently spread through the population and turned all the males into asexual females.
Scientists were, however, able to resurrect the lost male of the species by treating the female mites with antibiotics, which made them start hatching sons.
But getting rid of the bacteria doesn't return things to normal. In all-female wasps of Apoanagyrus diversicornis, the females rebuffed the returned males, having lost the instinct to mate with them. Fortunately, they can reproduce asexually.
Nothing like this has ever happened in mammals, as far as we know, says Beukeboom. But one type of lemming has fallen victim to genetic warfare, in the form of an X chromosome that attacks the Y. When inherited by a male, the selfish X sabotages sperm carrying the Y chromosome so that the carrier can produce only daughters.
The jewel wasps are sometimes victimized by an extra chromosome called a B chromosome that contributes nothing to the traits of the wasp. When a B-carrying male mates with a female, the B kills all of his genetic contribution to the offspring, except of course for itself, thus turning the male into a vehicle for its own spread.
"It's the most selfish genetic element known," says Beukeboom. In that case, the offspring all come out male, so it's the females that decline.
More often than not, however, infections and selfish genetic agents bias the sex ratio toward females, since species can soldier on with fewer or even no males, while losing the females means quick extinction.
As a representative of heterosexual manhood, English biologist Michael Majerus said this isn't necessarily a bad thing for any males spared. Quite a few science-fiction stories have allowed men to bask in female-biased populations, he wrote in his 2003 book, Sex Wars.
In a famous British series of books, Discworld, a character called Rincewind finds Nirvana on a desert island where all the men have been killed by a male-targeting plague.
"I wonder what proportion of men have had a fantasy of this type," Majerus said, "and what the female equivalent might be."