Across the entire phylum of arthropods, there is something that unites almost all of them. Beyond their genetics and their physiology that places them within Arthropoda in the first place, there is yet another facet of their biology that is shared. And often not in a positive way.
Your Actions Are Not Yours
Wolbachia is the name of a genus of bacteria and is largely considered one of the most successful parasitic species in the entire world. Lucky for us, it has nothing to do with humans, at least not directly. Instead, it infects millions of arthropods around the world and controls them for its own benefit.
Scientists have long known that Wolbachia is a type of bacteria that is able to directly influence and even take control of an individual’s actions. Its hosts are indeed the lucky ones though that they were infested with a bacteria that cares about their well-being, to some extent.
There are many a bacteria and especially fungi that do not have such high motivations and are instead responsible for controlling its hosts to death so that it can spread to more hosts. Now, don’t get me wrong, Wolbachia does this as well, but in a significantly different fashion.
Control Of The Children
Instead of trying to get its host killed, this bacteria takes advantage of the reproductive system of its host, finding ways to make sure that it gets passed on to offspring as well. This isn’t as straightforward as that, unfortunately for the bacteria, as it can only be passed down the matrilineal line, meaning that only infected mothers are capable of passing on the bacteria. Infected fathers and male offspring in general are of little use to it.
One method it uses to fix this is by altering offspring sex ratios. It is capable of ensuring that more females are born than males. Of course, it doesn’t make them all female, that would be counterproductive. Such a scheme would result in a population of only females, dooming itself in the process.
Instead, it alters the ratio just enough that slowly but surely, generation after generation, more and more of the species’ population is infected by Wolbachia. This in turn gives it more opportunities to infect other arthropods as well by association.
Only Approved Offspring Allowed
But it also has another method, a far more sinister one tied to reproduction. This actually has a proper title as well, it’s referred to scientifically as cytoplasmic incompatibility. As mentioned up above, infected males aren’t very useful to Wolbachia. And infected males mating with uninfected females just means offspring that aren’t infected with the bacteria. This is doubly bad, as it reduces the amount of infected population as a whole.
So, this sneaky bacteria takes things into its own pseudopod hands. Which it doesn’t have, pseudopods that is. When an infected male tries to mate with an uninfected female, it doesn’t work. More specifically, embryos are fertilized, but then die.
This is done in a particular way. The Wolbachia in the male alters its sperm production, a process called spermatogenesis, so that the sperm aren’t able to fertilize an egg. The mitosis event is delayed in their combination, meaning that only the egg chromosomes properly divide while the sperm does not. This results in a haploid offspring rather than a diploid one, which is nonviable.
Now, this process does still occur with infected males and infected females mating, since it is an attack on the male’s sperm ahead of time. But the female arthropod that is infected has a extra method, assisted by its Wolbachia, called rescue, where it allows proper splitting of both sets of chromosomes.
Sadly, the exact mechanisms of this process are still unknown.
Additionally, the exact genetics in the Wolbachia genome that create the process of cytoplasmic incompatibility have been researched for 40 years with no real results. Until now, that is.
Bringing War To Mosquitoes
In research conducted by the universities of Vanderbilt and Yale, both studies released simultaneously in the journals Nature and Nature Microbiology, they were able to identify the cytoplasmic incompatibility factor genes cifA and cifB. It required using transgenic methods and a model organism host in the common fruit fly (Drosophila melanogaster), but they did it.
The current plan is to use Wolbachia to infect dangerous mosquitoes, specifically Aedes Aegypti responsible for dengue fever, chikungunya, Zika fever, and much more. Prior research has shown that infecting the mosquito with Wolbachia causes the viruses causing the diseases to not grow and spread, essentially making the mosquito harmless.
What this new research discovered, in finding the genes controlling cytoplasmic incompatibility, is that by using genetic engineering techniques to insert these genes into insects infected with Wolbachia, it would actually strengthen the effect of stopping offspring from being viable if there isn’t an infected female involved.
The Enemy Of My Enemy
The hope is to then use this method to help spread Wolbachia even faster than it would normally spread in the wild, as the more A. aegypti mosquitoes infected, the less disease the population as a whole can spread.
Once they are all infected, perhaps we won’t have to get rid of the species altogether anymore. One can hope, at least.
Photo CCs: Aedes aegypti E-A-Goeldi 1905 from Wikimedia Commons