For context, I am primarily referring to Musca domestica.
Recently the thought occurred to me that due to short life cycle of the common housefly, and due to the fact that such flies have interacted with humans for thousands of years, it would be rather likely that human beings have served as an environmental factor that have affected the evolution of houseflies. Because of the short life cycle of the common housefly, would they been able to rabidly adjust to the environmental pressure of humans swatting them? Would the housefly of today be noticeably harder to swat than the flies of a thousand years ago? Would their be any way to know for sure?
Well that’s where your thesis goes amiss, that for Musca domestica being swatted by humans represents a any significant Darwinian or even Lamarckest selection pressure let alone one sufficient to induce either a rapid or rabid adjustment.
We can figure out a lot about evolutionary history by looking at various modern species and their phylogenetic relationship. Molecular phylogenetics gives us precise information about the relationship among species and the historical order and timing of their evolutionary divergence. So in principle, if there were multiple fly lineages that diverged fairly recently, and the species differed in their evasion response and their ecological association with humans, we could make inferences about the effect of natural selection in each lineage.
But don’t you think evading annoyed human swatters is probably going to be indistinguishable from a general predator evasion response that is much older than interaction with humans? If you want a PhD research project, the first experiment would be to compare the reaction times of Musca domestica with closely related species.
Neuroscientists have already developed experimental methods to look at this kind of reaction:
So you could start a collaboration with Dr Holmqvist and apply their methods to compare reaction times among various species.
More here. Musca domestica is a slowpoke compared to Condylostylus.
House flies, Musca domestica L., have a similar reaction time of 30–50 ms to a visual threat. The startle reflex of Condylostylus fly most certainly constitutes the fastest in insects, as it is 3–10 times faster than the previously reported reflex response times.
I do recall that the flies in the Australian outback were particularly lazy at evading swats or staying away from humans waving hands. I presumed this was because in the sparsely populated desert, they would have had minimal interaction in general with annoyed humans. Hence, the affection of the locals for wearing those hats with the fringe of dangling corks to keep presenting a bunch of constantly moving objects. I realize they are probably a different species entirely, but they look like houseflies.
Yes - Australian bush fly Musca vetustissima. As it says they are particularly fond of trying to walk on your face, and will risk a swatting to do so.
Since dung beetles were introduced fly numbers in Australia have plummeted. At school in the 70s we’d count the flies on each others’ back at assembly to win bets, but they are rare enough now that I don’t keep a flyswatter or bug spray at home, nor do I need a hat with the dangly corks. @penultima_thule might.
There’s surely been some selective pressure, but being swatted by humans is a quite uncommon cause of death for houseflies. They’re much more likely to get eaten by a spider or bird, or starve, or a variety of other calamities.
Now, granted, there’s some overlap. Flying faster or more unpredictably, for instance, will help against both swatting humans and against hungry birds. But they were already evolving that before humans became relevant.
There’s those giant mosquito looking insects that aren’t mosquitos that fly in an incredibly weird pattern seemingly changing direction at random which I read was an evolutionary response to predators.
I didn’t see specific study evidence cited, but this article refers to evolutionary pressures on a type of flycatching bird to more efficiently prey on flies, while flies are evolving in tandem to thwart them.
“There is an evolutionary pressure on the flycatchers to experience the ticking hand of the clock as slowly as possible in order to outwit their speedy prey. Over evolutionary time, birds that experienced ‘slower ticking’ could react faster to their prey, allowing them to eat more, raise more chicks and pass this speedy vision to future generations.”
“The flies that have been chased by the fast-sighted birds will be evolving faster reactions to get away. Creating an evolutionary arms race that has gone on longer even than the existence of birds. Prey flies have been evolving faster vision and reactions to escape predatory flies like the killer fly since they evolved flight.”
My techniques to swat flies have evolved as well. Wait till they’re grooming themselves before you make your move, and your success rate improves markedly.
Read about this plant in China which was massively harvested from the wild, so much so that the plant evolved better camouflage abilities in a short duration
Brings to mind Darwin’s anecdote about the Galapagos. While the ship was parked offshore, birds were landing on the ship and apparently had no fear of humans. He recounts how an officer was pouring a glass of water from a pitcher, and a bird landed on his arm to drink from it.
Then about 20 or 30 years later, when people had started settling the islands, one visitor recounts seeing a local boy with a 4-foot cane sitting near a watering hole. When birds came to drink, he would swat them with the cane and collected a dozen or more for dinner. The birds had already learned to stay a few feet away from humans.
I assume there’s something like a “skittishness” gene, and it has a “volume” setting. The ones with lower volume settings die, the ones with higher volume set survive, depending on predatory actions. Whereas, before humans came along, Nervous Nellies lost out comparatively when it came to getting food or water if they were too easily scared.
This is the same argument about North American megafauna extinction - the lifecycle time of mastodons etc. was not fast enough to “burn in” the lesson that humans could be dangerous and they were not populous enough to survive to get there.
Keep in mind that “survival” and “reproductive success” are not the same thing. Behaviors, coloration, vocalizations, etc., that increase reproductive success, but have a negative impact on long-term survival of the individual, may well be selected for.
Simple example: A fly that is cautious in the area it covers looking for food may survive longer, but it may significantly decrease its ability to mate and reproduce.
Yeah, the thought that female fly chicks might be really into those male fly guys who have the chutzpah to tick off humans with death defying acts is a concern.