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Just noticed some green bottle flies in my backyard. They are shiny. A shine like that attracts attention (of potential predators) and probably takes some work to maintain. This made me wonder why they might have evolved this. The Wikipedia article on them suggests this is used by males to identify mates.

It is further supported by this paper linked by @DkNguyen.

But common houseflies don't shine like that. They rely on pheromones instead. Why these very different strategies?

What surprises me is that the two fly species (green bottle flies and house flies) are probably closely related because they share so many other traits. And yet, their mating strategies are so radically different. I'm looking for where this branching off happened on the tree of evolution and what could have caused it.

My attempt at an explanation:

For the most part, I see the shiny green bottle flies outdoors. Either when there is poop, or a carcass or something with a strong smell. This seems to be supported by the following article: https://www.aardvarkpest.co.uk/blue-green-bottle-fly/

On the other hand, the common houseflies I mostly run into indoors where there aren't many strong smells from the things they might eat (which is not to say they necessarily evolved in this environment, just that it plays to their strengths). This suggests that the shiny green bottle flies are attracted to food that smells strong and that they are relying primarily on their sense of smell to seek out food. This probably means that if they use their sense of smell for finding mates too, it's going to overload that sense, causing them to not be as effective at finding mates and procreating.

This seems like a good reason for evolution to select for switching the mechanism of finding mates to one based on vision rather than smell in cases where the smell is relied on for other important tasks.

Are there any papers or other material to support or refute any of the reasoning in this chain?

Rohit Pandey
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    The guys dig it. Also, apparently they have good colour vision. https://www.sciencedaily.com/releases/2017/02/170214162804.htm – DKNguyen Aug 15 '21 at 04:23
  • @DKNguyen Want to turn your comment into an answer? – jakebeal Aug 15 '21 at 09:47
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    Not really, not since I don't think there is enough there and I don't really want to look further. There's probably something more definitive out there. – DKNguyen Aug 15 '21 at 17:34
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    Does this answer your question? Why do some bad traits evolve, and good ones don't? – Maximilian Press Aug 28 '21 at 23:55
  • Not quite. I get the general answer, but my question is more specific. The two fly species (green bottle flies and house flies) are probably closely related because they share so many other traits. And yet, their mating strategies are so radially different. I'm looking for where this branching off happened on the tree of evolution and what could have caused it. – Rohit Pandey Aug 29 '21 at 04:14
  • "Probably closely related" — is there some reason you haven't looked this up? Since one of the expectations on this site is that posters demonstrate prior research, doing that might improve this questions reception. However, the page linked by MaximilianPress is in all likelihood the best answer you will get — evolution has a large random component so trying to say why these two flies do things differently could require reconstructing the entire evolutionary and ecological history of these two flies and their ancestors ... – tyersome Dec 20 '21 at 00:38
  • Look up references that support that the two are closely related? I felt that was quite obvious, but I can do that. Also, while it might be true that MaximillianPress's answer is the best I'll get, I don't think answering this one is as hard as you're making it out to be. One plausible theory is that the common ancestor relied only on pheromones and that they were exposed to an environments where the smell signal was compromised (perhaps because of what they were eating), forcing them to slowly abandon the smell mechanism and switch to a more visual mechanism. – Rohit Pandey Dec 20 '21 at 01:55
  • Also, I think the fact that evolution is random is besides the point. It wouldn't work any other way. That's not an excuse to throw up hands and say "well, its random" :) – Rohit Pandey Dec 20 '21 at 01:55
  • They are in different families — I don't off the top of my head known how many millions of years of separation that represents, but flies have been around for 100s of millions of years and families represent some of the deepest levels of separation. 2) This means that there have been a (large) multiple of 10^8 generations (with random mutations) since the last common ancestor. Does that help you understand why the assumptions behind your question are naive?
    • – tyersome Dec 20 '21 at 06:37
  • I didn't know these two things, so thanks for pointing out. But still, I feel these alone don't say much; turtles and crocodiles have been fairly unchanged for 100s of millions of years and a mind boggling number of generations as well. I feel most traits of green bottle flies and house flies like the way they fly, speed at which they process information, lifespans, etc. have hit local optima and the way they look for mates is one of the few traits that separate them. Maybe I'm still naive, but I find the answer I posted satisfactory. – Rohit Pandey Dec 20 '21 at 07:07