A pregnant tsetse fly
The tsetse fly’s claim to fame is spreading the parasite that causes sleeping sickness in Africa. This public health concern has overshadowed much weirder facts about the tsetse, like the fact it gives birth to live, crawling larva—one at a time. (Sound familiar to you, mammal?) They also make “milk” to feed those larvae in utero, which uses some of same enzymes as mammals, according to new study published in the journal Biology of Reproduction. In fact, the sleeping sickness parasite is not even the most interesting organism living inside tsetse flies; no, that distinction would below to a bacterium called Wigglesworthia, without which females are sterile.
It’s time to take a journey through tsetse fly reproduction.
Insects are generally negligent parents: a female lays dozens or hundreds of eggs and flies off, leaving the young to fend for themselves. Most will die but a few will survive to lay hundreds more eggs and keep playing the numbers game. Tsetse flies, not unlike mammals, have taken the opposite tack, investing a whole lot of energy in each offspring. She keeps her eggs and larvae in the safest place possible for the longest time: inside her uterus. That’s the evolutionary explanation for live birth.
With a hungry larva to feed in her uterus, the tsetse fly makes a liquid rich in fats that scientists dubbed “intrauterine milk.” This new study found tsetse fly milk contains an enzyme called SMase that is activated in the acidic conditions of the larva’s stomach. SMase makes the fat molecules that form critical parts of cell membranes. This enzyme has a similar function in mammals—tsetse fly and mammal lactation probably evolved independently given the evolutionary distance between us and an insect, so SMase seems like a curious case of convergent evolution.
And remember Wigglesworthia? The researchers also investigated what happened to this bacterium living inside the tsetse when the gene for SMase was silenced. Without it, Wigglesworthia died off. That’s actually bad news for tsetse flies because the bacterium provides vital nutrients (not the important fat molecules) to its host. Females are sterile when they don’t have any of it.
All of these strange fact about tsetste fly reproduction add up to one encouraging conclusion about stopping the spread of sleeping sickness: a female tsetse fly doesn’t reproduce easily. One could hypothetically target SMase to disrupt pregnant flies, though large-scale, real-life applications for this research are far off. In the meantime, we’ll just have to revel in how oddly similar the tsetse fly’s reproduction is to ours. (Though they’re not the only non-mammal that gives birth to live young; for instance, DISCOVER recently covered an African lizard that gives birth to live young, and a recent study found a similar phenomenon in aquatic reptiles that lived 280 million years ago.)
Update: Want to watch a tsetse fly give birth to a maggot almost as big as itself? You have come to the right place. (h/t Ed Yong)
Image via Wikimedia Commons